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Sunday February 17, 2013

Ounces Versus Fluid Ounces

I’d like to go back in time and punch the guy who thought it’d be a good idea to force two different systems of measurement to share the same name.

Exhibit A: the ounce, a measurement of weight. You know, how heavy something is.
Exhibit B: the fluid ounce, a way of measuring volume; aka how much space something takes up.

The confusion begins with water. Water weighs one ounce per fluid ounce, leading many people to assume that the two terms are interchangeable, different ways of saying the same thing. Those people would be wrong (see Exhibits A & B).

coconut white chocolate Gianduja

It’s no coincidence water has a volume equal to its weight. The fluid ounce came about for the express purpose of measuring how much space an ounce of water would occupy. It didn’t matter if a jug was tall and skinny or short and squat; so long as it held ten pound of water, it was sold and taxed as a gallon (Imperial).

Originally, fluid ounces only applied to beer, wine and other water-like substances the government wanted to regulate. But in the late 1800s, American cook Fanny Farmer popularized using an eight fluid ounce “cup” as the basic unit of measurement for all ingredients. This was a huge improvement over the previous system, where recipes called for subjective measurements like “a saucer of flour” or “a lump of butter.”

Things got confusing somewhere between then and now when companies like Pyrex and Anchor began mislabeling their cup measures. Grab yours and take a look. You’ll find little red markings to indicate liters, milliliters, cups and ounces. This, despite the fact that measuring cups are physically incapable of measuring ounces. If you ever buy a compass from Pyrex, expect it to be labeled North, South, East and Hot.

I don’t have a problem with using cups to measure an ingredient if that’s what a recipe calls for. I have a major problem with manufacturers that systematically imply ounces are something you can measure in a cup.

Some people may roll their eyes and chalk it up to semantics, but by equating ounces to fluid ounces, these companies lead people to believe that when a recipe calls for 8 ounces of honey, they can get 8 ounces of honey by filling their cup to the 8 ounce mark. Unfortunately, thanks to a little thing called density, they wind up with 12 ounces instead.

The difference between 8 ounces of honey and 8 fluid ounces of honey isn’t semantics, it’s a quarter of a pound.

coconut white chocolate Gianduja

So whenever a recipe calls for cups, by all means grab your measuring cups! Keep using them to measure fluid ounces too. But when recipes call for straight up ounces, you need to use a scale, even for the liquids.

If you aren’t sure whether or not you should invest twenty five bucks in a scale, the first thing you should ask yourself is “how often do I have to convert recipes?” If it’s something you never do, you probably don’t need one. But if you spend any time at all Googling things like how many ounces are in a cup of flour, you may want to think about it. Especially considering the number one search result for that question is the wrong answer.

If you’re curious, read more about why I choose to measure my recipes by weight here:
Why Weight

White chocolate coconut gianduja

posted byStellaand filed under:  Sarah Jane

51 comments and counting

Feb 18, 2013 · 12:22 AM

Excellent essay Stella — my compliments! If I may contribute one suggestion/comment: go metric!
Here’s why:

1) No confusing terminology — milliliters & grams versus fluid ounces and dry ounces.

2) All metric measurements are based on a “decimal” system — meaning factors of 10 — and are therefore much easier to remember and calculate. (e.g. 1000 grams = 1 kilogram and 1000 milliliters = 1 liter; versus 16 dry oz in a pound and 32 fluid oz in a quart)

3) I, personally, find it MUCH easier to “measure” in metric units — no fractions! Just flip the switch on your scale to metric readings and you can measure weights to the nearest gram — very precisely.

4) For what it’s worth, 96% of the world uses the metric system. (The USA is one of last holdouts.)

I’ll get off my soapbox — and I realize that many (most?) will disagree with me. I’m not sure why there is so much “resistance” to the metric system in the USA, but for those that are willing to re-learn a couple of terms from grade school and give it a try, use of metric units while cooking can be very helpful. The hardest part will be finding recipes that specify ingredient lists in metric units. (I routinely “convert” my favorite recipes for future re-use.) Cheers!

 · Uchujin · 

Feb 18, 2013 ·  8:19 AM

I totally agree! Nicely said!

 · Joanne Fleming ·

Feb 18, 2013 ·  8:49 AM

I think part of the problem is that you rarely know if the writer of the recipe knows this, especially when you do like I often do and simply google a recipe 20 minutes before you want to get into the kitchen. Many home cooks have great recipes, but when they say “8 ounces of honey” but not one single other ingredient in the recipe was listed by weight, it’s probably fair to assume they are talking about one cup of honey. But I’m never quite sure, and it makes me hesitant to try out the recipe at that point.

 · Sarah · 

Feb 18, 2013 ·  8:54 AM

Baby steps, Uchujin, baby steps. Sadly, I still see the problem with metric. More than ounce I’ve caught a Brit posting a recipe from my blog on their own, using mL for the liquids. I even emailed one to let give ‘em a heads up of the mistake, but was told, “liquids are measured in mL not g.” Lol.

The primary reason I’m not an advocate of grams (aside from my raging patriotism) is that the most commonly available scales in the US are not sensitive down to the gram, even if they can “convert” to grams. I don’t want to tell people they have to go buy very specific, pricey scale X to get the job done. I want them to go buy ANY scale, even the cheapest one Wal-Mart has to offer, because my goal is to encourage people to try a new way of baking.

It’s a huge transition for people to leave cups behind and go to weight, asking them to jump to an entirely different system of measurement that is not commonly used in their home country is a bridge too far.

@Joanne, thanks lady!

@Sarah, you make an extremely excellent point. That cookbook authors (and bloggers) do this is pretty inexcusable, because they are supposed to be the “experts” and should not make their readers have to infer from context the meaning of a measurement.


Feb 18, 2013 ·  9:10 AM

Couldnt agree more! Or any less passionately!

When opening a restaurant, I went through 3 Sauciers who consistently got the sauces wrong. When the third messed them up, I realized they were all measuring fl oz when the recipe called for oz. They were all culinary school grads so I know they were at least taught the difference.

 · stephmce ·

Feb 18, 2013 ·  9:19 AM

P.S. (I’m with you on sticking with the Inperial system. Aside from the terminology nightmares, I like the system, itself. It may be my incredible stubbornness but whatever.)

 · stephmce ·

Feb 18, 2013 ·  9:38 AM

Oh my god! The #1 search result on google for a cup of flour’s weight IS wrong! What is this I can’t even. Excellent blog post! I’m totally sharing with my fans on FB!

 · Jason S ·

Feb 18, 2013 · 10:26 AM

Stella, what a fantastic post! I think this confusion is also the reason so many home cooks find cooking so difficult and say that it all goes wrong even when they follow a recipe.

- Nan

 · Silver Magpies ·

Feb 18, 2013 · 11:04 AM

I love this post! Thank you for writing about this topic. Recently someone asked how to divide their cupcake recipe…well, if you weighed your ingredients you wouldn’t have to wonder what half of 1 3/4 cup of flour is!

I converted my recipes so I can weigh them. I get more accurate results this way.

 · Flower · 

Feb 18, 2013 ·  1:16 PM

Preach it sister! I hate that guy, he’s right up there with Daylight Saving guy. And no matter how clearly you put WEIGHT OUNCES people will still measure 6 ounces of chocolate chips into a measuring cup and yell out you when the cake comes out wrong.

 · Jackie @ TheBeeroness ·

Feb 18, 2013 ·  2:09 PM

ahhh, that’s why your gianduja recipe did not turn out! thanks!

 · Kathryn · 

Feb 18, 2013 ·  3:45 PM

I haven’t been baking much lately, but you know I’m on the scale bandwagon

 · Melissa ·

Feb 18, 2013 ·  4:11 PM

@stephmce, omg, Imperial solidarity!! Together forever!

@Jason, I know, right?! I feel bad for people who go the extra mile and seek outside confirmation, only to have the wrong answer validated…

@Nan, agree agree! Education is the answer.

@Flower, oh man, dividing cups is a nightmare. The only thing more frustrating than half an egg is half of 1/3 cup.

@Jackie, dude let’s banish Mr. “Fluid” Ounces and Daylight Savings guys to their own island of confusion.

@Kathryn, oh! That would explain a thing or too. Long lost mystery solved!

@Melissa, xoxo


Feb 18, 2013 ·  6:39 PM

Weighing is king! While I am personally firmly on the metric side, I do believe the unit of measure used is secondary in the argument. Being born in Hong Kong living in a Chinese community while raised in Australia, I am often exposed to Chinese units of measure, and I’ll tell you, it’s tough juggling metric, imperial and traditional Chinese measurements!

In any case, I currently work part time as a kitchenhand in a Dim Sum kitchen in Melbourne, and everything is done by weight—with the exception of water. Small units are weighed on traditional Chinese scales (that look like this, while larger units are measured on the 25kg mechanical scales.

But certainly, Sarah’s comment raises the greatest issue. While we “enlightened” ones, no longer weighed down (I promise, no more puns) by incorrect measures may know how to get precise and repeatable results, recipies out there may or may not be listed correctly. And then you have to sit there and figure out what exactly they were trying to do. }=[

 · KayDat · 

Feb 19, 2013 ·  2:45 PM

i had a hard to time getting my prep cooks to understand this concept… they liked to measure everything with measuring cups, even if it indicated OZ in weights, so the sauces and baked goods quality differed greatly between individuals. i rewrote all of the pastry recipes in grams to fix that…

 · ila ·

Feb 19, 2013 · 10:04 PM

@KayDat, that is so fascinating! Thanks for the link to the scale, btw. Your job sounds awesome. It is really unfortunate that anyone has to put up with an author or chef’s incorrect use of the terms in a book/recipe. Instead of educating their readers (as a chef and author should!), they add to the confusion.

@ila, I’ve encountered this a terrifying number of times in the professional kitchen too.


Feb 20, 2013 · 10:47 PM

Thank you Thank you Stella!!!! You are pretty awesome!!!! Love your recipes. WOnderfully written, made a lot of sense to me,especially about fluid ounce measurement. When will you finish your book, can it be pre ordered?

 · Gerryberry · 

Feb 22, 2013 · 10:01 AM

Hi Gerryberry! I’m so happy to clear things up, especially with the puddin’ confusion, it got me thinking that an explanation was in order. Thanks for stickin’ with me. I don’t know when it’ll all go down, but you’ll definitely be able to preorder. Probably will make lots of announcements a few months before the book comes out (Autumn 2014).


Feb 22, 2013 ·  3:13 PM

This is such a great post and something thats super important. I remember when I just started baking… oh lord. I had no idea about any of this stuff! Now I have a scale, its changed my baking so much. I just bought a mini scale that only measures up to 100 grams, but goes to .01 of a gram. I’m hoping it will make things ever more consistent/awesome in da kitchen.

Also you’re writing a book! Wonderful. Can’t wait to read it. You have such wonderful and interesting recipes here.

 · ElizaB ·

Feb 23, 2013 ·  3:09 PM

Hi Eliza! Your gram scale sounds hardcore! It's cool how the more precisely you bake, the more you become aware of how tiny variations can change the results from batch to batch. With cups, most people chalk that kind of variation up to luck of the draw or some random, weird incident. But there’s always a reason!


Feb 27, 2013 ·  2:03 PM

This is probably one of my biggest peeves with recipes and in the kitchen. I think it’s the former chemist in me that gets my hackles raised whenever someone (who should better) emphatically states that 1c of flour is 8oz. ARGH! I’m a scale-fan myself and it’s the best tool in my kitchen, out flanked only by good sharp knives.

 · AnnieB · 

Feb 27, 2013 · 11:56 PM

@AnnieB, uuuughhhh, right? And whenever someone says, “a pint’s a pound the world around!” I just wanna shout, “EXCEPT IN ENGLAND WHERE IT’S 20 OUNCES!” Which is probably why no one ever invites me to parties…


Mar 02, 2013 ·  1:14 AM

I wish political dealings made as much sense as this posting

 · Marilyn · 

Mar 04, 2013 · 10:32 PM

Hey Stella,

Here in Denmark, I have found this measuring cup from Oxo Good Grips:

Can you recommend it for liquid measurings?



 · MacaronThief · 

Mar 05, 2013 ·  9:14 AM

Hi MacaronThief! I love Oxo’s products, I think that’s a great cup. I can’t see the “ounces” section, but the OXO cup my parents have is marked “fluid ounces,” which is a wonderful reminder to people that ounces and fluid ounces aren’t the same. I don’t use a liquid measuring cup for any of my recipes (all weight!), so I haven’t ever put it to the test myself, though.


Apr 02, 2013 · 10:41 AM

Hi Stella. Being from the UK I’m definitely a grams and millilitres kind of girl. However as long as their is a weight and no cup measurements I know I can easily convert the two which makes me a very happy girlie! Thank you this informative and useful blog post. Much love x x x

 · Corky · 

May 13, 2013 · 11:44 AM

Correction to something written above: you can measure liquids in grams. You can measure anything in grams, even gases (though that can be tricky owing to buoyancy, which also affects weighing very low-density things like meringue and marshmallows). I actually prefer recipes to be all in grams or dry ounces so I can measure straight into the mixing bowl on the scale. The big advantage with pounds and ounces is that they’re easy to scale recipes up and down owing to how nicely the fractions work. Doing this in grams involves remembering more digits, and I can do without the extra steps of writing things down when baking.

A hint: 1 ml water or milk weighs so close to 1 gram that you’ll never know the difference in cooking.

 · Freddie · 

May 14, 2013 ·  9:47 AM

Hi Corky, do scales in the UK let you convert to ounces, by chance? Wondering if manufacturers have started to include it, given the transatlantic interest in baking and the internet bringing all recipes to all people.

Hi Freddie, yes absolutely! Let me know where you see the error, I’m missing it. As a unit of weight, grams can absolutely be used to measure the weight of anything. As converting between ounces and fluid ounces, it can be tricky converting between fluid ounces and grams, though. As you mention, things like milk are no problem at all, but things like honey change the game.


May 30, 2013 ·  6:30 PM

Hi Stella!! I am new to your sight and I love it!!! So insightful and easy to comprehend. It’s funny that I came across this blog because last night I was measuring out mini marshmallows for my raspberry chocolate crispy treats and it called for 10 oz. so I got my scale out but it didn’t seem like a lot. The bag itself was 16 oz. and the 10 oz. I weighed out was less than half of the bag where I would think it would have been more closer to 3/4’s because of the weigh measurement on the bag.

Although you really can’t mess up crispy treats, I wanted to know why the measurement was so much different than the weight. When I weighed the whole bag of marshmallows, it weighed almost twice the amount that it says on the bag. Needless to say, I was pretty confused. I have always “used” (past tense) measuring cups and have just recently purchased a scale, I am practicing making French Macarons…love ‘em!!

Thank you for your awesome site…see you here tomorrow!!

 · kreative1 · 

May 30, 2013 ·  9:57 PM

Hi kreative1! Oh wow, that’s a huge difference! I’m not sure how to account for that. Just to be certain, you might try weighing out a stick of butter to make sure it clocks in at 4 ounces, or a cup of water (8oz).

Sometimes a one pound box of brown sugar will weigh 18 ounces, but the marshmallow situation sounds so far off base I’d want to rule out some sort of mechanical error just to be safe. If things look accurate, then I guess you just got the lucky jumbo pack of marshmallows!!


Jun 18, 2013 ·  7:16 PM

Thank you for making this distinction so beautifully. I was just making chili and was bemused to discover that an 8 oz can of tomato sauce came out to only 3/4 cup sauce when measured. I forgot about the ounce/fluid ounce distinction. The cans were labeled by weight, not volume.

I gather that the pyrex labeling is intended for water only or for liquids of a similar density. Since I am certain almost no one out there is aware of the distinction, the labels are very misleading. There are probably a lot of recipe failures attributable to it.

 · Clare · 

Jun 20, 2013 ·  9:47 AM

Hi Clare, I had something similar happen the other day. Bought a container of corn syrup and I thought it said “32 ounces” and I was thinking, boy this sucker is heavy! Then I looked closer and is said 32 fluid ounces (so it weighed 48 ounces plus the weight of the bottle).

Yeah, the Pyrex cups are just meant to measure out water and milk and really basic stuff like that, where it’s all close enough. But as recipes have evolved (we use way more interesting ingredients now than we did in the 50s!), people are using those measuring cups to measure a much broader range of ingredients that rarely coincide with 8 ounces a cup. But I’m really surprised there’s no legal issue with them genuinely mislabeling their product. Ughhhh….


Jul 23, 2013 ·  5:46 PM

LOL @ “North, South, East and Hot.”

So true…

I’ve been meaning to look up this difference for a long time now. Finally have the confirmation I need.

Short and sweet. Thank you!

 · Bobby ·

Jul 26, 2013 ·  4:22 PM

Hi Bobby. So happy I could clear things up, happy baking!


Aug 01, 2013 ·  2:24 AM

Haha, love the post!

Although, what’s up with the photos? Are they ice creams scoops, lumps of honey ball goodness, mad scientist balls? And what do these balls have to do with the post? Just checking, hehe.

 · Preeti ·

Aug 01, 2013 ·  9:17 AM

Hi Preeti! They’re scoops of white chocolate coconut gianduja; there’s a link to the recipe at the very end of the blog post. Nothing to do with the blog post per se (aside from the fact that you need to use a scale to make it), just some eye “candy” since I thought pictures of scales would be pretty boring, haha.


Aug 20, 2013 · 11:06 AM

when are fl oz. and oz equal? and when are they not?

 · toribee · 

Aug 20, 2013 · 11:16 PM

Hi toribee! That’s a great question! They’re only equal with water, or with things that have a similar density to water, like apple juice or milk. Otherwise, fluid ounces and ounces work out quite differently.


Aug 30, 2013 ·  6:53 PM

I love using a scale but for recipes that deal in volume conversion can be tricky. It’s best to look at the nutritional label; the serving size usually contains volume and weight so use this to convert. The weight is often listed in metric grams even in the US so it might be a good idea to get comfortable with metric. I always use a kitchen scale but if you are trying to “scale down” a recipe written in volume you can convert to tablespoons or teaspoons. 1 cup is 16 tablespoons or 48 teaspoons. So cutting 1/3 cup in half to 1/6 cup would be 8 teaspoons or 2 tablespoons and 2 teaspoons.

 · Justin · 

Sep 04, 2013 ·  5:17 PM

Correction (yeah I’m being that guy)…fluid ounce(vol) and ounce(mass) are not actually equal when dealing with water. Assuming a density of 1g/cc, then 1 fl oz of water will have a mass of approximately 1.043oz. Aside from that, I would love to time travel with you and punch stupid people in the face! Shall we go, you and I while we can? Through the transitive nightfall of diamonds. Take care and great post!

 · K · 

Sep 04, 2013 ·  9:57 PM

Hi Justin! Oh, yeah, converting to weight from volume can be a real pain, so much can go wrong. But that’s a smart idea about looking at the package (of sugar/flour/etc) for details. Thanks!

Hi K! Okay, so this is blowing my mind. How does that work exactly? I mean, I get the density/weight/volume issue, obviously, but my understanding was that a fluid ounce was designed in every way to be the physical representation of an ounce of water by weight…. So, whaaa? Clearly, it’s mega close, but still. Is this an issue of Imperial ounces versus avoirdupois or some such? Madness. Anyhow, yes, let’s have a punching adventure!


Sep 06, 2013 · 10:50 AM

The term fluid ounce was once used as a measurement of a certain weight of fluid (wine, water, ale, etc.); however, the US fluid ounce has been defined as 1/128th of a US gallon. The US gallon is based off of the old British wine gallon (a cylinder container measuring 7in diameter and 6 inches high, and later rounded up to 231 cubic inches).

I usually drive myself to near insanity trying to figure it all out!! When I first stumbled upon this blog, I was in the middle of calculating fill level for a customer of mine (I am a packaging engineer). They wanted to know where the fill level would be for 32oz of water in a specific package and so I started by assuming 32 fluid ounces. Later, I found out that they were weighing 32 weight ounces of water and filling the package that way. So I recalculated for weight ounces and it was a different fill level. Being the kind of guy I am, I couldn’t stop there. I HAD to fully understand it inside and out!! Then when I stumbled upon your post, I was like, c’mon now K!! What the hang am I doing wrong here? I spent the past 3 days recalculating and wrapping my brain around this whole mess and I finally understand…kind of. I’m glad it’s Friday!

So who else is on your “to be punched” list?

 · K · 

Sep 07, 2013 · 11:21 PM

woah…. mind = blown. Also, your career sounds fascinating!

Hmmm, let’s go punch everyone who asks “is that Celsius or Fahrenheit?” when I say to preheat an oven to 350. God bless the soul who bakes their cookies at 350 C!!!!!


Sep 27, 2013 ·  6:37 PM

this was very enlightning, funny, and all aroung fun. I being the one who thought nothing of what “Weigh” something meant. but if you think about how we humans weigh ourselves…has anyone tried to get a big enough measuring cup to weigh themselves? I think not. they get out a scale and look at what they weigh. So if you read directions and it says eight ouncec of celery, get that scale out. where as if you said get 12 ounces of whatever liquid, then by all means get that measuring cup out. Very cool article.

 · Irishman · 

Sep 29, 2013 ·  4:09 PM

Hey Irishman! Close, but not quite. If a recipe calls for 12 ounces of a liquid, you still need a scale! Ounces is always a unit of weight, regardless of what’s being measured. Recipes that want you to use cups should call for “fluid ounces” specifically.


Feb 19, 2016 ·  9:30 AM

This explains why my Martha Stewart scale includes among the possible modes ounces, grams, or fluid ounces. I have always ignored the FL oz mode, because how could you weigh volume…?! So Martha believes that all fl oz = oz ? Guess she skipped tat day in, what 1st or 2nd grade science!

 · michele · 

Feb 19, 2016 ·  9:32 AM


 · michele · 

May 10, 2016 ·  4:02 PM

Thank you. I did no know this. And thank you for comments keep it up guys

 · MCG · 

Jun 28, 2016 · 11:06 AM

Hi Stella,
Having moved from an all metric country (South Africa) to the UK where they use both I was super confused. Thanks so much for your article!
You had asked about scales in the UK in an earlier comment? Indeed most scales do measure both here. But that’s because the UK were late in the game adopting metric as they were the origin of the Imperial system (Imperial meaning of the British Empire, haha!) But in the 70s when the UK joined the predecessor to the European Union they had to adopt metric to make measures standard across the bloc. So the dual labeling is a hangover from the past rather than a new adoption.
In conversation with people here (especially older folks) they almost exclusively use Imperial. In writing it is almost exclusively metric though often both are used on packaging.
Hope that helps and thanks again for clearing this fluid/weight thing up. If you and K need backup on your mission to punch your way through history I got your backs

 · Tk · 

Jun 28, 2016 · 11:42 AM

Oh, seems I flubbed my dates there. Metric only became the legal standard in the UK as late as 1995!!

 · Tk · 

Sep 15, 2016 ·  7:50 PM

Hi Stella,
Thanks for the info. My question arose from the local grocery store selling gelato as 32 fluid ounces. The actual weight of the product, container and cardboard label was 18 ounces. This just seems like another way to trick the consumer. Buyer beware!!

 · SKL · 


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