How to Read an Appliance Label for Watts and Amps

The rating label is a small sticker or plate that states what an appliance needs from the wall. Read it first, before you plan anything around it.

Where to look

Labels hide in plain sight. On a fridge, check inside the cabinet near the door edge or on the back panel. On a pump or power tool, look for a metal plate on the motor housing or a sticker near the cord. Small appliances often carry the label on the underside.

You're hunting for a few lines. Expect something like a voltage, a current in amps (A), a frequency in hertz (Hz) and a power in watts (W) or volt-amperes (VA). Not every label shows all of them. Some show only amps.

If you can't find a label, the manual is the next stop. Failing that, the maker's support page for your model is a fair place to ask.

What the units mean

A watt measures the rate of energy transfer¹. Volts are the electrical push. Amps are the amount of current flowing. They connect by a simple sum: volts times amps equals watts, as one maker's guide puts it, Volts (V) × Amps (A) = Watts (W)².

So when a label gives only voltage and amps, you can work out watts. Say you read a plug-in appliance marked with a voltage and a current. Multiply the two. The answer is the label's power in watts, with one catch, covered next.

The catch: watts and volt-amps

Some labels say VA instead of W. They aren't always the same. A reference page on the volt-ampere says that with a purely resistive load, the apparent power is equal to the real power³. Where a load has an inductive or capacitive part, such as a motor, the apparent power is greater than the real power³.

The gap between them is the power factor. Resistive loads have a power factor of almost 1, while loads with motors can have a power factor well below 1⁴. In practice:

• A kettle or toaster: volts times amps gives you a sound figure for watts.
• A motor: volts times amps may give a bigger number than the real watts.
• A backup unit rated in VA: compare it against the VA or amps on the label, not only watts.

If you're unsure which unit a number is in, don't convert it on a hunch. Ask the maker.

What the label usually leaves out

Look hard at the label and you'll often find the running figure and no startup figure. A starting figure covers a brief burst at switch-on, lasting two or three seconds according to one maker². Check whether your label or manual gives one.

If it doesn't, leave the space blank and ask the maker. A blank isn't a failure. It's the honest state of what you know, and a guess dressed up as a number is worse.

Using what you've read

Take the numbers to your backup unit's own label or manual. Compare the running figure of the appliance to the unit's continuous rating. Then compare any startup figure to the unit's surge rating. The next page, surge and continuous ratings on an inverter, explains those two ratings.

Keep a few cautions in mind. Don't open an appliance to look for numbers inside; the label on the outside is what the maker meant you to read. Don't alter the wiring of an appliance to suit a smaller backup unit. And if a plan involves connecting a battery system to the house circuits or the switchboard, that's licensed electrician work, full stop.

For the reasons behind the startup gap, read why motors surge.