Not sure why anyone would calculate how many km's driven on the size of the tank. You never fill it up when empty. I always calculate km's driven and amount to fill on each tank.
Usually use an excel file to quickly calculate. For some reason I can not attach excel files or I would share it.
2004.5 LLY GMC Duramax 3500 Quad Cab SRW Long Box
Tan leather interior -DVD-loaded
KB Mouthpiece, AMSOIL Synthetic engine and trans fluid
Autometer Cobalt Boost and Pyro
MBRP 4" Exhaust
Quadzilla Stealth 2