The amount of "cum" a person produces will vary all the time. Sometimes I cum enough to fill 2 or 3 shot glasses (never tried, just estimates), and then other times I'll produce enough to fill a teaspoon

It depends on how often they had masturbated in the past few weeks (not masturbating for a week will usually produce a big, think load).

The diet also helps out, if a person is eating all the right foods as part of a balanced diet, they can often create bigger loads.

Tiredness and/or stress can influence as well apparantly.

It's all little things that add up to the end result.