system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Cumshot

Why is it that sometimes it shoots out but other times it just dribbles out? What affects it?
gpt
On average, guys ejaculate about 1 teaspoon-worth of semen in one ejaculation - about 5 mL - which is not a large amount.   The amount (volume) of ejaculate will be a little more if it's been awhile since you ejaculated and less if you ejaculated recently.

A man's body is constantly producing sperm and storing it up for ejaculation.  This gets mixed with fluid produced by the seminal vesicles and prostate.  Apart from frequency of ejaculation, the amount of time spent in sexual activity and the amount of arousal can also affect the volume of ejaculate.  The longer the build-up, arousal, and direct stimulation prior to ejaculation, the more volume of fluid can be produced to mix with sperm for ejaculation.  Some men also have noticed that this increase in ejaculate volume with longer stimulation also produces a waterier semen because of the increased fluid to sperm ratio.

So it stands to reason that if you are dehydrated, your volume will probably be less.  Other factors that affect it are getting proper amounts of zinc in your diet, getting good sleep, stress levels and your frequency of ejaculation.  Genetic factors and age also play a part, but those are not under your control.  Strengthening your PC muscles can produce stronger contractions on orgasm and help push out more fluid.