Don't give up yet because this is what I do. First, remember it's not rocket science and a couple % MORE oil than what you plan won't affect the power one bit.

My measuring equipment consists of one used plastic bottle of ordinary lawn mower oil or whatever. The one with a clear graduated scale on the side. OK, in Australia it's easy because it's a 1 litre bottle with 100cc graduations and I don't know what they might be marked with in America. If they're graduated in ounces then a quart bottle will be 32 at the full mark and I'd imagine has 4 ounce divisions. Just noticed that you've got a gas engine as well. If you can mix the fuel for that then you can do the same with methanol.