Rui, which aircraft are you working with? Weight & Balance is my speciality (B747F). I don't quite understand your question.
OEW Operational Empty Weight (includes crew, catering, unusable fuel) + cargo (or pax) = Zero Fuel Weight + Fuel = Ramp Weight (or taxi weight) - taxi fuel = Take Off Weight. TOW - BurnOff = Estimated Landing Weight.
If you have some specific questions, I'm happy to help.