This form will help you work out electrical power values.
Simply enter the two values you know into the relevant boxes, leaving the third box blank.
For example, to work out the maximum power of heater you can run on a 13Amp fuse from the mains, enter '13' in the Current box, and '230' (the UK mains voltage) in the Voltage box. You will get the answer of 2,990W, or 2.99kW.