Is it ever more accurate to measure by volume rather than by weight?

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.

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.

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).

"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...)

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.)

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.

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.

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.