Japanese cooking measurements are different from the United States. American 1 cup is 240ml, but Japanese 1 cup is 200ml. It’s a big difference particularly if you are baking. Teaspoon and tablespoon sizes are the same.
Also Japanese recipe is usually measured by weight, not by volume.
Japan used to use own volume measurement system “go” and “sho”. 1 go is 180 ml, and 10 go is 1 sho. Japan switched to metric system, but old system is still used mainly for sake and rice. The traditional big bottle of sake is 1 sho (1800 ml) and the half size is 5 go (900 ml).
A measurement cup which comes with a rice cooker is also 1 go (180 ml), following this tradition. That’s why you always should measure rice with the cup which came with the rice cooker.
The recipes I list in this site use American measurement system, except rice. So that when I write 1 cup of water in a recipe, it means 240ml of water. But 1 cup of rice is 180 ml.