Does anyone know how to calculate electricity costs for different appliances but using watts, amps etc?

1500 watt unti running for an hour will use 1.5 kilowatt hours.

1000 watts = 1 kW (kilowatt)

if you have current (amps) and voltage (volts), then multiply amps times volts to get watts.   in europe, most things run at 220 volts, in US 115 volts.

if you have horsepower,
1 horsepower = 745.699872 watts
so multiply number of horsepower times 746 to get the number of watts

once you have the kW, multiply this times the amount of time you run it for.  for example, 10 minutes = (10/60) hours = 0.167 hours

if you're running it a whole month, that's, call it 30.4 days ( average) = 30.4*24 = 730 hours in a given month on average.

when you multiply kW times hours, you get kWh or kilowatt-hours.

ComEd in the city of Chicago charges 8.275 cents per kilowatt-hour as of my last electric bill.  so multiply your number of kilowatt-hours times 8.275 and that's how many cents you're paying.

So, your 1500 watt appliance, run for a whole month costs:
1.500 kW * 730 h * 8.275 cents = 9061 cents = $90.61

And this is why the rated watts number is deceiving...your fridge even doesn't run 24x7; it runs for a while, and then it goes quiet (stops running).  your computer's power supply is rated at 400 W, but your computer spends 99% of its life running below that number.  Pretty much all appliances work this way.

The only time this calculation is truly reliable is with a light bulb.

For appliances which you know the draw (watts) simply take the number of watts divide by 1000 to get KW (kilowatts) times cost of power (I pay 8.5 cents a KW/hr) times the number of hours used.

example a 100 watt light bulb on all month

100/1000 = 0.1
0.1*24hours*30days*8.5KW/hr = 612 cents

or 6.12 dollars a month

power(watt)=voltage* current..