Hi, I have a nordic track treadmill, problem is it has a USA plug on it and needs a stepdown converter, I got a 100watt one and it blew, the spec is

0-10 MPH
1-10% power incline
1.5 continuous HP motor
15 amp circuit breaker
120 VAC 60Hz

Can anyone pleae tell me which watt stepdown converter I need to buy because I haven't got a clue

Start by telling us what country you are in.

Or you could call Nordic Track and have them replace the US components with the correct one for your country.

As to wattage, you know the voltage is 120VAC and The Amperage is 15 so the formula is W=V*I or W= 120*15, W = 1800.

Sorry I'm in England, our plugs are 240 as apose to 110, the treadmill was given to me