To calculate the right size of the resistor you need the characteristic data of the load cycle: brake time or duty cycle and the total cycle time. Furthermore you need the brake power Pbr and the minimum resistance value Rmin which is defined by the VFD.
Due to production tolerance and temperature coefficient the recommended resistance value is significantly higher than the minimum resistance value. Here we use a safety factor of 20 % (R = 1,2 x Rmin), effectively preventing possible damage to components of the VFD due to high currents.
Would you like to Calculate Continuous Power (Pcont) from a known Braking power instead?