…from an august academic contributor who prefers anonymity.
Measurment & Conversion
First, I like to think that assload is an SI (metric) unit whereas buttload is imperial. That would make me happy.
So 1 assload = 1 liter-newton. Specifically, the volume of water multiplied by the force exerted by the sphincter that is necessary to retain it.
Small Ass vs. Large
Same amount of water retained in a smaller ass requires more sphincter force, so the assload value is higher.
Double the water in a 2x larger ass requiring about the same force also has a 2x higher assload value.
Double the water in the same ass means more sphincter force and more volume, so the assload value is doubly higher.
This, my friends, is science.