How to convert watts to amps

1. The watts-to-amps formula

Electrical power, current, and voltage are tied together by the power law:

where P is power in watts (W), V is voltage in volts (V), and I is current in amps (A). Rearranging gives the two most useful forms:

• Watts to amps: I = P ÷ V
• Amps to watts: P = V × I

The formula works for any resistive load (heaters, incandescent bulbs, kettles). For motors and inductive loads the relationship is the same but the true power (watts) may differ from the apparent power (volt-amps) because of power factor — for most household purposes the difference is small enough that the simple formula gives a useful working figure.

2. Standard voltages by country

The voltage you use in the formula depends on your country's mains supply:

In the US and Canada, standard outlets are 120 V. Large appliances — electric dryers, ranges, water heaters, and EV chargers — typically run on 240 V (a split-phase circuit). In the UK, Australia, and New Zealand all standard outlets are 230 V single-phase.

3. Worked examples

Example 1 — Hair dryer (1,500 W)

A typical hair dryer is rated at 1,500 W. On a 120 V outlet:

At 120 V this is 12.5 A — close to the limit of a 15-amp circuit. Running another significant load on the same circuit risks tripping the breaker.

Example 2 — Microwave (1,000 W)

A 1,000 W microwave on a 120 V supply:

Example 3 — How many watts can a 15-amp circuit supply?

Rearranging to amps → watts: P = V × I

That is the theoretical maximum. In practice, most electrical codes require that continuous loads (running for more than three hours) must not exceed 80% of the breaker rating, giving a usable limit of 12 A or about 1,440 W on a standard residential circuit.

4. Common appliance wattage and current draw

Typical wattages and the resulting current at 120 V. Check the appliance label or specification sheet for the exact figure — the values below are approximate typical ratings.

† Requires a dedicated higher-amperage circuit. High-wattage appliances (dryers, water heaters, EV chargers) typically run on 240 V in the US/CA. Wattages are typical published industry values, not code specifications.

The key takeaway: lower voltage means higher amperage for the same wattage. An electric kettle rated at 2,200 W draws 10.00 A at 120 V (if a 1,200 W model). This is why kettles sold in the UK and Australia heat water faster than US models — the higher voltage allows a higher wattage on the same amp-rated circuit.

5. Why watts, amps, and volts matter

Understanding the relationship between watts, amps, and volts is useful in several everyday situations:

Checking whether an appliance will trip the breaker

A 15-amp circuit can continuously supply a maximum of 15 × 120 = 1,800 W (at 80% continuous load, about 1,440 W). If the total wattage of all appliances plugged into that circuit exceeds this figure, the breaker will trip. Convert all the wattages to amps using I = P ÷ V and add them up — if the total exceeds the breaker rating, you need to spread the load across circuits.

Sizing extension leads and power strips

Every extension lead has a maximum amp rating. Divide the total wattage of all devices you plan to plug in by the supply voltage to get the total current draw, then make sure it stays well under the lead's maximum. Using an undersized extension lead is a fire risk.

Reading your electricity bill

Electricity is billed in kilowatt-hours (kWh). A 1,000 W (1 kW) appliance running for one hour uses 1 kWh. To convert watts to kilowatts, divide by 1,000: 1,500 W ÷ 1,000 = 1.5 kW. Running a 1,500 W space heater for 8 hours uses 1.5 × 8 = 12 kWh. Multiply by your rate per kWh to get the cost.

Generator sizing

When sizing a portable or standby generator, you add up the wattage of all loads that need to run simultaneously. Converting each appliance's amps to watts (P = V × I) and then summing them gives the total watts the generator must supply.

6. Amps to watts — the reverse conversion

To go from amps back to watts, multiply by the voltage: Watts = Amps × Volts. This is useful when you know a circuit's amperage and want to understand the power capacity:

• A 20-amp circuit at 120 V can deliver up to 20 × 120 = 2,400 W (2.4 kW).
• A 30-amp circuit at 240 V can deliver up to 30 × 240 = 7,200 W (7.2 kW) — the typical rating for a home EV charger.
• A 100-amp service at 240 V has a theoretical capacity of 24,000 W (24 kW) — the maximum a whole-house panel can deliver at once.

Use the Amps → Watts mode in the calculator above to do this conversion for any combination of voltage and current.

For more on electrical circuits, see the voltage drop calculator (how voltage loss over wire length affects your appliances) and the voltage drop guide.

Common questions

How many amps is 1,500 watts at 120V?

1,500 watts at 120 volts draws 1,500 ÷ 120 = 12.5 amps. A hair dryer or 1,500-watt space heater pulls 12.5 A — close to the limit of a 15-amp circuit. Use the watts to amps calculator above to check any appliance at any voltage.

How do you convert watts to amps?

Divide the wattage by the supply voltage: Amps = Watts ÷ Volts. This is a rearrangement of the power formula P = V × I. Example: a 1,000 W microwave on a 120 V circuit draws 1,000 ÷ 120 = 8.33 A. On a 230 V supply: 1,000 ÷ 230 = 4.35 A.

How many amps is 1,000 watts?

At 120 V: 1,000 ÷ 120 = 8.33 A. At 240 V: 4.17 A. At 230 V: 4.35 A. The voltage determines the answer — enter your voltage in the calculator for the exact figure.

What is the formula for watts to amps?

I = P ÷ V, where I is current in amps, P is power in watts, and V is voltage in volts. To go the other way (amps to watts): P = V × I. For example, a 15-amp circuit at 120 V can deliver up to 15 × 120 = 1,800 W of continuous load before the breaker trips.