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I've been thinking about the fact that although many recipes specify volume, measuring by weight is much more accurate.

Are there any cases where it would be objectively better (i.e. more accurate) to measure by volume - that is where a weight measurement would leave you scratching your head?

I'm really thinking theoretically here: if you're just trying to come up with a reliable, reproducible way to measure an ingredient, perhaps so you can write down a recipe for yourself, would you end up always using weight or are there cases where volume would be more precise? Cases where they are equally accurate (such as water) don't count.

This question is not regarding the practicality of different ways of measuring but rather the accuracy.

I've thought of a few borderline cases, but I was wondering if there was anything more straightforward:

  1. When serving a whole "unit" as a portion, such as a baked apple, one would count the number of apples to prepare rather than getting a total weight - although it would probably be a good idea to weigh them afterward to figure out how much of the other ingredients to use.
  2. A garnish might be measured by volume - it doesn't really matter how much the whipped cream on top of the brownie weighs as long as it covers it.
  3. When greasing a pan, one needs the volume necessary to cover the pan, but no one ever measures this.

Reminder: This question is not about what's subjectively better, or what you think I "should" do, just what's accurate.

Update: I guess I started a bit of an interesting discussion here, but there are only a couple answers that gets even close to what I was looking for. I'll try again: An person preparing food in a kitchen somewhere on dry land on earth, can measure most items by either weight or volume. In some of those cases weight will be more reproducible than volume (such as flour or salt) and in some of those cases there will be no difference (such as water). Are there any cases where using weight will cause more difficulty than volume - that is the volume is more relevant than the weight.

Two more cases:

  1. when filling something (say a pie shell) or making equal layers (thank you rackandboneman and rumtscho) if the mousse came out more or less dense than you intended, you need to use the same volume, and the weight is irrelevant.
  2. when the ingredient is not so precise to begin with, such as "x mL jarred tomato sauce" will surely cover the pasta, but "y g jarred tomato sauce" may not

Again, no question about practicality or personal preference here.

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    "measuring by weight is much more accurate" - I don't understand this. A liter of water is as accurate as one kilogram of water. What are you trying to say here? – Davor Nov 4 '15 at 14:39
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    @Davor It is actually true in many cases. For example, dry ingredients can have variations in packing, so one cup of flour isn't always the same amount of flour, but 5oz is. For ingredients that stick to the measuring cup, it's tough to get the full correct volume. And even if the ingredients cooperate, it's sometimes harder to measure a volume accurately than to measure the corresponding weight accurately. Of course there are also cases where volume is totally fine or even better, but that's what the question's asking. – Cascabel Nov 4 '15 at 14:58
  • I've removed all of the discussion about accuracy, leaving the two above comments which make it abundantly clear that there are in fact plenty of accuracy issues. If you have something to say about the accuracy of various methods, write an answer. – Cascabel Nov 4 '15 at 21:07
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Better is a subjective term, however you can see what is done in practice as a guide to what people think is generally efficient as a balance of preparation speed, accuracy and cleanup.

Many recipes use a combination of volume and weight. Volume for most liquid measurements like milk, water or stock is considered more efficient than weighing them because although weighing is more accurate in most recipes the differences are small enough not to make a difference.

Weight is generally considered more efficient than volume for larger quantities of dry ingredients or gels (butter, lard, shortening) as it's faster, more accurate, and less cleanup.

Small amounts of wet and dry ingredients like spices, herbs, powders, flavorings etc are usually measured using volume measurements like teaspoons and tablespoons. I've tried it both ways and I've found that using teaspoon fractions is much faster than trying to weigh out small amounts of ingredients, and that my scale isn't accurate enough to weigh the fractions of grams you'd need to get that level of accuracy.

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    For what it's worth I tried to remove the "better" so you don't have to worry about subjectivity. – Cascabel Nov 4 '15 at 18:08
  • If you just have one scale that goes up to a couple kilos (my usual one does 3000 g), measuring 1 g is a bad idea. But you could buy another scale for smaller measurements (I got a 100 g scale that reads in 0.05 g increments) then problem solved! – Nick T Nov 4 '15 at 20:12
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I can't list all cases, but there is a rather simple way to decide.

First step: ask yourself whether you have a complicated chemical or thermodynamic reaction going on in your food. If yes, you probably need to stay within the ratio in which the reaction happens as expected, and this means ratio by number of molecules or atoms available for the reaction. Kitchens don't have the equipment needed for counting molecules, but the nice thing is, in both solids and liquids, this amount is directly proportional to weight (but not volume). So, you have to measure by weight. If you measure by volume, you'll have to deal with strange, unworkable textures in your final results. This is because volume is a bad approximation for weight when it comes to kitchen reality. While in theory, the density relation is simple, you're not dealing with solid chunks of stuff here.

Most examples from this class are from baking (e.g. dough hydration), but they can also happen in cooking, such as the ratio of yolk to water in mayonnaise.

If you don't have such a reaction, ask yourself as a second step: Do you need to fill something? If you have a prescribed volume, such as a mold, a pie shell, a fruit or bird to be stuffed, you should calculate the final volume and can work to it backwards. Note that this case is less problematic than the first. You can just work without any measurement, eyeballing it using a high estimate, and then deal with any leftovers (which tend to be tasty).

A special subcase will be when you're working with mixing liquids, for example for cocktails. Some liquids don't sum up their volume when mixed, alcohol and water are a good example. So, you have to measure the first liquid in whatever unit you want, and then fill up with the second to achieve the needed volume (assuming you need a fixed end volume). If you were mixing weights, you couldn't choose the proper weight to mix in order to get the final volume.

Third step: If neither of the above applies, ask yourself: what is most convenient for you? When you don't need a fixed weight or a fixed volume, you have three options: weigh it, measure the volume, or eyeball it. Because in this third case, accuracy doesn't matter, the best is the one which brings you to the result with the highest speed and least hassle.

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One example would be if you are making something mostly liquid, and what you want is a final volume. For instance, would you make a Negroni (one third gin, one third Campari, one third vermouth) by weighing the ingredients? Apart from the fact you'd need to adjust based on different densities, this would be ridiculous given getting a known volume is the desired outcome.

Bringing this back to something closer to cooking, one needs to recognize that accuracy is not the only criterion. If I have a recipe for milkshake consisting of a half pint of milk, a banana, a couple of scoops of ice cream and a few drops of vanilla essence (made up out of my head), weighing might be more 'accurate' in some way, but would be far less convenient and would add nothing to the outcome.

We Brits are, however, confused why our US cousins like to use volume measurements for dry ingredients like flour, particularly as we don't treat a 'cup' as a fixed size measurement (I know it is in fact a defined volumetric measurement in the US).

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    The milkshake example here isn't bad - I don't think all brands of ice cream would weigh the same amount, so a weight might mess things up. – user40292 Nov 5 '15 at 19:02
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"one apple" measures by number not volume, "grease for a pan" is more of a "quantum satis" thing (if what you cut off for doing that is not enough you will take more, if it is too much you will discard or reuse the rest of the grease), and garnishes can be imprecise in actual amount, proportion to the rest of the dish is more important.

The big problems with volume are:

  • Commonly used spoon/cup measurements can be imprecise, and even worse express unclear ratios if the recipe writer used eg a tablespoon that is not 3 teaspoons, or a cup that doesnt have 16 tablespoons, or mixes heaped and flat spoons, or mixes cups/spoons of unclear volume with weights.

  • Volume of anything but a liquid is hard to measure accurately, short of immersing the material in a liquid - which might spoil it. And measuring the volume usually needs whatever you measure with contacting the material, unlike a scale that you can leave under a mixing bowl into which you pour stuff from above. I always wonder how "you americans" don't have huge problems with stored ingredient spoilage due to cross-contamination via uncleaned measuring spoons ;)

  • Aeration/packing can alter volume drastically

Of course there will be actual cases where you need volume measured:

  • layered desserts etc. where you want layers of equal thickness
  • mixtures that you want to fit in a given container when finished
  • ANYTHING that needs to fit a container for the next steps (baking pan, pot, food processor bowl, pie shell...)
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    If you want to add to your answer, simply use the edit button. Please don't use comments for that purpose. – Catija Nov 4 '15 at 15:05
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    Not sure about the rest of the country, but we just have multiple sets of measuring spoons to avoid contamination. Or I wash one... – JPhi1618 Nov 4 '15 at 15:28
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    I can counter that by saying "commonly used scales can be imprecise". Just buy decent ones. If it says "1 metric teaspoon" on the handle, I assume it's 1 metric teaspoon. I have as much reason to believe the measuring cup as I have to believe the scale. – Willem van Rumpt Nov 4 '15 at 16:49
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    @WillemvanRumpt While I do agree, at the same time, while my cups and teaspoons are nice and trustworthy, they are hard to find outside the US, and become confusing when transferring recipes. Weights are generally more universally standardized these days. – NadjaCS Nov 4 '15 at 19:56
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    The issue is not so much inaccuracy, @WillemvanRumpt, as imprecision: with volume measurements of dry goods, it's much too easy to get different amounts each time you make a measurement with the same cup, or when two people use the same cup. Unless the scale is truly awfully constructed (or broken), it will give you the same measurement every time (whether that measurement is slightly off or not). This doesn't necessarily help when cooking a recipe one time at home, but when developing or reworking a recipe to be used often --and by other people -- on the same equipment, it's important. – Josh Caswell Nov 4 '15 at 20:11
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Volume is more precise* than weight when dealing with quantities small enough to approach the measurement limits of your scale. This is true of most measurements up to a tablespoon or so.

If 1/2 teaspoon of a powdered spice weighs about 2 grams, and your scale measures to grams, then your weighed amount might actually be anywhere from 1.5 to 2.5g. That is at least as variable as the usual measurements for the variability of scooped flour, and most spices don't compress as dynamically as flour. The difference is even more dramatic for liquids which don't compress at all.

This is why European recipes and many pro recipes that otherwise use grams often use volume for everything a tablespoon or smaller. It's not just convenience. It's increased precision.

*Talking about decreased variability is more precision than accuracy. Accuracy is that the results are circling the correct bullseye; precision is hitting the same mark every time, whether or not it's the right one. End pedant note.

(I'm two years late, but I haven't seen this perspective listed as an answer.)

  • I'd like to partly disagree: I think the teaspoons (or "tip of knife") for spices are used because only low precision is expected anyways: The variability, say, between any two different curry mixtures, or the same fresh vs. 1 year old means that even high precision in the dosing won't lead to high precision in reproducing the flavor. So spice dosing is typically adjusted by direct measurement of flavor. This changes if you look e.g. into (modern) recipes for sausage dough, where tasting is not possible. – cbeleites Apr 7 '18 at 15:17
  • I totally agree on the small end of kitchen amounts it's easier and cheaper to use volume than mass - but that's because the required balances are expensive whereas judgment by eye can work for volumes down to few microliters. I'd therefore still say it is a matter of convenience (including the cost of tools to help with these measurements). (Whereas in the lab, we check the calibration of our pipettes (volume measurement) with a balance...) – cbeleites Apr 7 '18 at 15:19
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Weight will usually give a more precise measurement, simply because it is easier to get high-precision balances than it is to get an equivalent precision in glassware. However, in the kitchen, volume is almost always easier to use and faster to measure out.

So the answer to your question is: volume is better whenever precision doesn't matter as much, mass is better when it does. When does it matter? Usually in baking. In everything else, there is a lot more room for error. That's why professional baking recipes often give measurements in mass (especially of dry ingredients, where the density can vary substantially), but most other recipes use volumes. For things like spices, the intensity of the spice can change so much that it doesn't make sense to try to be extremely precise - you have to adjust it anyway to taste.

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Are there any cases where it would be objectively better (e.g. more accurate) to measure by volume - that is where a weight measurement would leave you scratching your head?
This question is not regarding the practicality of different ways of measuring but rather the accuracy.

Yes.

Weight is mass that is affected by gravitational acceleration. The effective gravity varies by altitude and latitude.

Volume is mass in three-dimensional space and therefore not affected by gravity, but by density. Density again can be controlled by pressure and temperature, which is much easier to control than gravity.

So, using volume to measure the mass is more accurate everywhere and every time, if you don't care about the practicality.

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    I think you're saying that astronauts should use volumes, or other people if they're under unknown acceleration ... which are cases I hadn't thought about, but makes sense. Although most people on Earth wouldn't be in those situations, I can think of one -- chefs on ships, where the ship's motion would screw up any weight measurements. – Joe Nov 4 '15 at 21:21
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    This seems more like a joke answer. As long as you're on Earth (and I'm pretty sure the OP isn't asking about cooking in space), the variation due to gravity is tiny - about 0.3% from sea level to the top of Everest, which is less than even the precision on a typical kitchen scale. (Besides, you also seem to assume that volume is a precise measurement method, which it absolutely is not in practice.) – Cascabel Nov 4 '15 at 21:23
  • @Jefromi The question is about the best accuracy, which is explicitly repeated at the end of the question again. Your argument that no one needs that much accuracy does not invalidate my answer. – John Hammond Nov 4 '15 at 21:26
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    Lars, I view your answer as totally unapplicable to the context. This is not physics.se, we are talking about the difference between following a recipe which uses weight measurement of ingredients, and a recipe which uses volume measurements of the same (usually non liquid) ingredients. The fact that using volume when the density is well known doesn't matter, because 1) the density isn't known, and 2) the error margin of 0.3% is not significant for cooking. – rumtscho Nov 6 '15 at 16:09
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    @rumtscho Again: The question itself states that it is a question about theoretical accuracy and practicality is of no concern. Where is the difficulty in understanding this? If you think my answer belongs to physics.se, which is a valid opinion, then the question belongs there too or needs to be edited so it is about practical accuracy in the kitchen. I've written mostly food science answers and nobody ever came up before with:"That's science, who cares about that much of detail?" – John Hammond Nov 6 '15 at 18:15
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It's a good question, but it's really a matter of what the recipe says and what tools you have available. Not everyone has a scale, and to be honest a scale that produces a level of accuracy that's any better than volumetric measure is too expensive for 65% percent of households (I made that number up). Additionally, although I would like to have a scale, I have other tools that I would prefer to buy first. I suspect that is the case in most kitchens.

Regarding whether it's better? Again depends on the recipe. Most recipes are volumetric or by the each and is usually dry measure. So to get dry measure, you scoop up some stuff in your spoon or measuring cup, and scrape off the top without packing down any of the ingredient.

If you use the same tool on the same ingredient and measure it the same way every time, I bet if you measured it say 10 times, that the results would be close enough every time. Close enough meant to mean the difference will have no measurable affect on the outcome of the dish.

Now there are certain fancy ingredients that need to be spot on, but those aren't usually in the average kitchen.

Even with a perfect recipe, we adjust as we go. That 1 tsp of cumin might not really be enough, maybe I'll use 1 and a half tsps.

So although cooking is indeed chemistry, we don't need to be so accurate as a chemist does.

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    I strongly disagree with your statement about the expense of a good scale. Good scales can be had for $25-40. If you are going to make stuff up, it doesn't belong in your answer. – Catija Nov 4 '15 at 15:08
  • @Catija not everyone has spare money and a scale probably isn't at the top of there must get this next list. – Escoce Nov 4 '15 at 15:26
  • Your answer makes it sound like scales cost hundreds of dollars... which they don't. – Catija Nov 4 '15 at 15:27
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    I think perhaps there is the difference between objectivity, subjectivity and frame of reference. For some people hundreds of dollars is a non-issue, for others $25 is a big deal. So, you thought it sounded like hundreds of dollars, that's because of your frame of reference where hundreds of dollars is a lot, for most people 100s of dollar is a lot more than just a lot. Whereas my statement was merely comparing expense to importance, and spending $50 for a scale that really offers no real gain in cooking or eating experience, that is a lot of money. – Escoce Nov 4 '15 at 15:32
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    There is probably a regional difference what is considered standard equipment - you could walk into any german department store and leave with a kitchen scale, but you might or might not get a set of measuring spoons. And an inaccurate scale is OK as long as it is linear and used as the sole measuring device. – rackandboneman Nov 4 '15 at 17:23

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