Average amount of semen in ejaculate?

My husband and I are trying to have another baby, but since our first was born his ED has gotten much worse, to the point where sex is no longer possible (he's a type 1 diabetic and has been for 35 years...drugs like viagra no longer help). We're using the home "turkey baster" method where he ejaculates in a cup, and then we use a needless syringe to inject the semen. We had our first go round today, but when he brought me the cup, I was shocked at how little there was...I never really noticed or measured before but then, I never collected it in a cup before eitehr:) I was figuring there would be about a teaspoon, but there was far less....maybe an eighth of a teaspoon? Is this a lot less than average, or am I just going to have to work on and perfect my semen-sucking-syringe strategy?