As a rough guide engine oil usually weighs about 0.87 kg/litre or about 7.2 pounds per US gallon.
Unfortunately a rough answer is the best that can be done as there are hundreds of different types...
I don't know if you are saying you have the new hubs and rotors and still have pulsation, or if you are asking what causes pulsation.
If you have pulsation on slowing this is due to warped rotors,...
Jack up rear of car, use axle stands for safety. Ensure handbrake is off. Remove rear wheel, a single small Posidrive grub holds the drum to hub. Sometimes if high mileage a rim is left on the outer...