Well kg make sense, doesnīt it ?!
Or do you load passengers and cargo also in liters?
If you have indication in liters you have to calculate for mass and balance.
And it isnīt that hard to convert - either with rule of thumb, Jet Fueling App on the smartphone or with the old mechanical computer ;-)
(or make a note in your book - 100liters = 80 kg // 125 Liters = 100 kg // 20kg = 25 liters) the rest is easy ;-)