Both chain load and chain speed are required in order to evaluate the chain life duration. These parameters can be directly input, or calculated when specifying actual engine power and rotary (or linear chain) speed.
If the force in the chain strand is not known, the power of the motor can be taken as an assumption. However, keep in mind that the so calculated engine power could be much higher than the actual needed power: the selected chain could then be over dimensioned for the required application. If chain speed may vary, please input the lowest speed, since the chain pulling force is maximal at a given constant engine power.
Please also pay attention to the chain maximum admissible linear velocity, since this velocity is limited depending on the chain size: