The USDA recommended serving of rice (PDF) is 1/2 cup cooked, which should be 1/4 cup raw, as rice about doubles in size.
The reality, though, is that the amount someone should eat and the amount someone does eat is not usually the same.
This can be seen in the wide variation of serving sizes listed on various sites. This one that talks about serving sizes specifically and recommends 1/2 cup uncooked per person or less:
When it comes to rice the norm seems to be about ½ cup (90g) per person, although some people prefer to use a bit less – about 1/3 cup (60g) per person. And remember we are talking about uncooked rice here, which means that when it’s cooked it’s usually about a cup per person, as rice doubles in size. For a main meal this is definitely enough!
While this FAQ from a US rice brand clarifies that the portion size listed on their packages is 1/4 cup uncooked:
The serving size refers to 1/4 dry (uncooked) product; this is the equivalent to 3/4 cup of cooked rice.
(Their rice is apparently really fluffy when cooked)
This is likely because they're following the USDA guidance for serving size in their package labeling.
So, if you're cooking for just a few people, I recommend erring on the high side (1/2 cup uncooked per person) but if you're cooking for a big crowd, you'll probably be ok with smaller portions (1/4-1/3 cup uncooked).
The general rule for white rice is to double the amount of rice to get the amount of water you should use but your rice maker should have instructions about this.