How much semen does the average man ejaculate?

I know that this is a weird question, but I'm quite serious Unfortunately, I'm also a private person, and so I'm much too shy to ask anyone face-to-face. My question is this: what is the normal amount of semen that an average man delivers upon ejaculation? I ask this purely out of curiosity, because since I was a virgin until marriage and had no experience even on a lower level of sexual intimacy, I have no baseline by which to judge my current circumstances. I should explain that my husband delivers about 15 to 20 ml and sometimes even more, which seems a prodigious amount judged by the standards of other women I've listened to. He also seems to recuperate and be ready for sex again very quickly by these same, albeit hear-say standards ~ in less than an hour in fact, when he delivers almost as much semen again. And if he holds back some of this semen [which he is learning to do by muscle controle exercises] he can be ready again in just minutes, which allows us to make love several times in the space of a few hours Don't get me wrong, I'm NOT complaining! Our sex life is phenomenal and I've learned to love his very 'wet' brand of lovemaking, not to mention his stamina and recuperative powers. Nor am I bragging, I assure you ~ and I DO realize how lucky I am! But I AM also very curious, so can anyone out there enlighten me? I should add, that I am twenty-four and my husband is thirty, we have one little boy and another child on the way, and we have been married for three very happy years.