Which expands more when cooked: brown rice or white rice?
I'd say the answer will depend a lot on the exact type of rice, as well as cooking method, and how much you might "fluff" it afterward. I've seen internet sources that claim brown rice expands more, and other internet sources that say white rice expands more.
For a more precise measurement, I went to the USDA food composition database. There you can find measurements of nutrients by volume for cooked and raw rice. Although volume measurements are difficult for things like cooked rice, I figure if there's any resource that attempted consistency in measurement, it's probably something like this.
Anyhow, what I did was compare the calories listed for 1 cup raw vs. 1 cup cooked rice in various instances from the USDA nutrient list. I assume there aren't a lot of calories randomly lost during cooking (or at least any minimal loss is at similar rates). Note that the standard USDA preparation seems to be to cook until all water is absorbed (for example, in data sheet here), rather than methods like boiling in excess water and draining, which could result in more nutrient loss.
So, by comparing the calories per cup in raw vs. cooked, we can get a sense of the relative expansion of each variety of rice. Here's the data for calories per 1 cup portions, along with my calculated expansion ratio.
- Long-grain: raw 679, cooked 248 = ratio 2.74
- Medium-grain: raw 688, cooked 218 = ratio 3.16
- Long-grain: raw 675, cooked 205 = ratio 3.29
- Medium-grain: raw 702, cooked 242 = ratio 2.90
- Short-grain: raw 716, cooked 266 = ratio 2.69
- Glutinous: raw 684, cooked 169 = ratio 4.05
Bottom line is that the shape and type of rice grain seems to matter just as much as whether it's brown vs. white. Again, there are bound to be inaccuracies here, so I'd only take these figures as estimates. But there doesn't seem to be a significant trend that brown rice always expands more or less than white.
My instinctive answer is that brown rice expands more than white. Because my family made rice a lot while I was growing up, and I'm really sure I remember that brown rice is made with a lot more water per cup than white (half to a full cup more water per cup of rice), and the grains after cooking are plumper and fluffier - that is, there's more volume in cooked brown rice, and the grains look more similar before cooking than after so it isn't just a question of different starting points.
So I would guess there's extra water being absorbed by each grain, even if some extra is also being lost to evaporation, and more water being absorbed by the rice means more volume where the extra water is, in brown rice rather than white.