What's the size of the plastic cup that came with my rice cooker?

Assuming you bought a rice cooker designed by a Japanese company (and apparently even other brands tend to meet that market's expectations), the measurement is 1-gou, slightly more than 180ml, which, by no coincidence, is also the typical measure of a wooden sake, cup, and is closely associated with a historical sake bottle size (approximately 1.8l)

http://en.wikipedia.org/wiki/Masu_(Japanese)

It turns out that this amount, 1 gou of dried rice, neatly corresponded to a typical serving of rice. In practice, most contemporary Japanese eat about 1.5-2 gou per day; 1 gou of dried rice cooks up enough for 2 Japanese adults for one meal if you have several side dishes. There are other measurements that derive from the gou (or perhaps the other way around), such as the koku, which was considered the amount of rice that a single person would consume over the course of a year.

This is one of the human-centric forms of measurement that has survived the metric push; you can find various examples of this in many otherwise metric-converted countries. It turns out some studies show that those metrics often make certain categories of estimation easier for people.

Edited to cover the concern about matching the right amount of water:

It's worth noting that you don't need perfect precision for the amount of water, as long as you cook with the full cycle and not one of the express cooking modes. I can't remember the exact scientific principle behind it, but perhaps something to do with osmotic pressure. Some people use the remarkably effective method of measuring a certain amount of space between the dried rice and the water based on the size of their forefinger segment or thumbnail. It apparently works well for almost any imaginable size of pan (though you can have other problems with a pan too wide to have the rice cover the bottom). (Some types of rice do prefer more water than others, but within a single type, you have a fairly flexible range for the water ratio)

The plastic cup that came with my rice maker was 180 ml (3/4 cup). It's an odd size, but that's the standard.

I have an Aroma brand cooker (Got Rice GRC-003) and also lost the measuring cup. Their site tells you if you ever lose the cup, use a standard 3/4 cup and observe the water marks in the pot.

http://www.aroma-housewares.com/kitchen/appliances/rice101/21/Rice%20Measuring%20Cup.html

Hope this helps.

I have an Aroma automatic rice cooker. Its directions says "The measuring cup provided adheres to rice industry standards (180ml) and is not equal to one U.S. cup (240ml)." 180ml is equal to 0.76 U.S. standard cup, so use 3/4 cup standard measure of rice to their water measure line in the steaming pot and it should cook correctly.

I'm struggling with this too, as I replaced my rice cooker cup. However, as someone else pointed out, ratio counts. It's one cup of white rice to one and a half cups of water. Doesn't matter if it's American standard cups or Japanese metric cups. The proportion is what counts. And it's one cup of brown rice to two cups of water. So, if you're using the 180 Gou as a measure for rice, then use 180 Gou plus 90 Gou for water (for white rice).

Your rice cooker is probably metric, so I'd think in terms of milliliters rather than cups. Now if it were me, I'd use the link in @Aaronut's comment to make rice and forget about it, however if you want a pretty good estimate then simply measure out how much water it takes to fill to the 1 line, then divide it by 3. Again, use ml, it's much more precise.

I know its been a while since this thread has been run, however, as a rule, most rice cookers also respond well to a 1 rice to 2 water ratio, however take care as some units require a minimum to successfully trigger at the end of the cooking process.

My rice cooker is a small Cuizen 16 cups and came with this cup, which as you can see holds 2/3 cup, or 160 ml.

I also lost my multicooker rice cup and stumbled onto this thread since I had the same problem as Daren.W. I finally figured out that serving sizes are 3/4 cup of uncooked rice. So the manufacturers provide a 3/4 cup dry measure for our convenience since standard measuring cups are 1/4, 1/3, 1/2 and 1 cup.

Use any size cup (coffee cup, juice glass, tea cup) for rice, then add water to a ratio depend on the type of rice: 1.5 of the same cup of water for white rice 2 of the same cups of water for brown rice

So, for instance: 2 coffee cups rice + 3 cups of water for white, or 2 cups rice + 4 cups of water for brown rice.

Your lost cup was, most assuredly, a guo (or "go"). I appreciate being able to put in my 3 go measures of short grain white rice and add water to the appropriate marked line, and not having to actually measure the water in a separate cup. A go is one-tenth of a "sho." A "to" is 10 sho; a "koku" is 100 sho.

My wife and I love Japanese food, but often make American versions of it. Onigiri and Rice Bowls are a staple in our house. We don't have a lot of side dishes. We get a different bag of rice almost every time and have never used the plastic measuring cup. And the markings on the side of the pot don't actually go low enough for our usual rice usage. (They start at 2 cups, when we just want 1 cup)

1 cup (240mL) of dried rice makes enough onigiri that we are full at the end (roughly one large and one small for each of us, depending on fillings). Some rice requires a 1:1 ratio, and other rice requires a 1:2 ratio. Most of the time, it's a 2:3 ratio. (One and a half cups water to one cup rice) You have to determine the right ratio for your rice.

Sushi rice tends to respond well to more water. Jasmine rice tends to respond well to less water. Different brands will affect it, as will different tastes. We haven't tried brown rice. Broken Jasmine is simultaneously undercooked and mushy no matter what we do.

So whatever you go with, it's definitely a YMMV moment. I would start at 1 cup rice and 1.25 cup water, or if you prefer the smaller rice cups that come with the machines (gou), .75 cup rice and 1 cup water.

If you measure the water before you put it in, you can use internet recipes or general ratios to calculate how much to put in. Once the little cup is lost, you may as well just forget about the lines and use standard cup measurements.