Why are there so many calories in raw garlic compared with raw onion?

One serving of raw garlic (1 clove) has 5 calories in it and one serving (1/2 cup) of raw onions is 27 calories. Garlic has less calories per serving, but you tend to use more than 1 clove in cooking as ompared to 1/2 cup of onions, so the calories add up more quickly for garlic than for onions.