You need to get a scale capable of measuring weights down to grams to two or three places beyond the decimal point. If you're either into reloading small arms ammunition or dealing drugs, you probably already have one of these scales. If not, you will find one on eBay for somewhere between one hundred and three hundred dollars.
Then, you need to get yourself some small aluminum pans, about three inches across or so. Put one on the scale, tare it, take it off, blow your load into it, then weigh it.
Semen will always have a specific gravity very close to 1.0 since it's mostly water. Trace amounts of its more exotic constituents will have a minimal effect on that.
If your load weighs 5 grams, congratulations- you just blew 5 milliliters, which is considered the upper limit for "normal". If you blow any more than that, you're nothing short of exceptional.
If your load weighs 1 gram, guess what - you're still normal.
Anywhere between 1 and 5 mL is considered normal.
Most of my loads fall short of the 1 mL "normal" cutoff because I jerk off so many times a day I never get a chance to restore. The biggest loads I've blown fall between 2.5 and 3.5 mL and they were quite impressive.
Anything above 5 mL is colossal and should be awarded a trophy. A shot glass is 50 mL and anyone claiming to be able to fill one will naturally be met with reasoinable skepticism.
Take a look at the video in my gallery of me blowing a load onto a pillow. Now, I know it's not the biggest load anyone's ever seen, but it is substantial. It's about 2 mL, to put it all into perspective.
Enough for now. | 
