Hopefully someone will post an answer for you, but in case they don't, then you can safely estimate by paying attention to how much you drain out of it. Put roughly that much back in, checking the dipstick as you go. Once you get close but not over, start it up so that the filter can fill up, then check it again. Top it off based on the dipstick. It is a little more work, but it can be done safely. I just had to do it with a Bobcat skid steer, with a Kubota engine in it. It held almost 2 1/2 gallons!