We remember the formula as WAV - Watts = Amps x Volts

By dividing both sides of the formula by amps you get - Watts / Amps = Volts ... the amps / amps on the right hand side canceling each other out to leave volts.

And by dividing both sides by volts you get - Watts / Volts = Amps ... the volts / volts on the right hand side canceling each other out to leave amps.

Examples

Q What is the biggest electric fire that can be run on a 13 amp fused plug in the UK?

A Mains voltage in the UK is 240v so Watts = 13 x 240 = 3120 watts or just over 3kW

Q A 60 watt car spotlight is showing a drain of 5.5 amps on the ammeter. What is the voltage?

A 60 / 5.5 = 10.9 volts

Q A food mixer with a 400 watt motor runs in the US on 120 volt supply. What fuse to fit?

A 400 / 120 = 3.33 amps. A 5 amp fuse would be ok.