The simple answer for how you convert watts to amps is to divide watts by volts to get amps.
Amps = Watts ÷ Volts
If you have 1000-watts and 120-volts, then amps is equal to 8.33.
In the world of home inspections, the most common reason to convert watts to amps is to determine the size of circuit breaker (and wire gauge) that is suitable for a home appliance.
If you hook up a water heater that is rated at 4000-watts and use a 15-amp breaker — it is going to overheat or constantly trip.
Convert Watts To Amps With The Ohms Triangle
An easy way to look at converting watts to amps (or amps to watts etc.) is through a triangle.
You take one value (amps, volts, or watts) and if you divide it by the other value either above it or below it — it will convert it to the value on the side. The watts should always be on the top of the triangle as you can see from below.
Clothes Dryer 6500-Watts (Example 1)
Let’s say you have an electric clothes dryer that is rated at 6500-watts and it uses 240-volts.
So… 6500-watts ÷ 240-volts = 27.08-amps.
And if you round up from 27.08-amps then you would need a breaker of at least 30-amps.
The wiring (gauge) should also be able to handle it. A 30-amp breaker would need an 10-awg copper wire.
Microwave 1800-Watts (Example 2)
Imagine you want to install a new microwave that pulls 1800-watts. It will need to be on a individual or dedicated circuit and say it uses 120-volts.
So… 1800-watts ÷ 120-volts = 15-amps
So at minimum you would need a 15-amp breaker. The wire needs to be at least 14-gauge for copper.
The Concept of Watts, Amps, And Volts
The easiest way to think of amps, watts, and volts is to think of it as water.
Imagine you are powering a water wheel with a hose. There are only two things that you can increase to make the wheel turn faster, the water pressure or the volume of water.
The water pressure is the voltage, and the volume of water (per second) is the amps. And when you multiply the pressure and the volume per second — you get the power (watts) of the water wheel or how fast it turns.
Wire Gauge Must Match Breaker
As stated earlier, if you plan on upgrading a circuit for an appliance, you can’t just swap out a breaker. The larger amp breaker needs to match the capacity of the wire.
In the U.S. and Canada, wire size is called A.W.G. or American wire gauge. The smaller the gauge, the larger the wire. The most common size for branch circuits, regular outlets and lights, is a 14 gauge wire coupled with 15-amp breakers.
Aluminum Wiring Is Only For Larger Amps
Most service conductors are copper and aluminum. Aluminum is usually reserved for higher amp circuits, and aluminum wiring that is used for 15-amp, 20-amp, and 30-amp breakers will go into my home inspection report as a possible defect.
But for 40-amp and above, aluminum single strand is totally fine.
|Breaker Size||Copper Wire||Aluminum Wire||Common Uses|
|15-amp||14-awg||*12-awg||Outlets/Lights, Fridge, Dishwasher|
|20-amp||12-awg||*10-awg||Kitchen GFCIs, Microwave, Fridge, Washer|
|60-amp||6-awg||4-awg||High Watt AC Units|
*Aluminum for lower amp circuits is a possible defect
Watts To Amps Conversion Table
Below is a simple conversion table for wattage to amps…