Convert between watts and amps using voltage and current type
This converter helps calculate the relationship between electrical power and electrical current. To do that, voltage is needed, and for AC circuits power factor is often needed as well.
In DC circuits the relationship is more direct. In AC circuits, power factor matters because the current and voltage may not be perfectly in phase.
For many simple DC devices, watts divided by volts gives amps directly. For AC appliances, using a realistic power factor gives a more accurate result.
For related calculations, see the Length Converter and Multiple Measurements Tool.
More background on electric power is available here: Electric power reference
This electrical unit converter converts between watts and amps using voltage and current type. The calculations apply to DC circuits and to AC circuits where power factor is known. The reference material below covers the key formulas, practical examples, and a conversion table for common appliance power ratings at both 120V (US/Canada) and 230V (UK/Europe).
Three values describe the behaviour of an electrical circuit:
Two formulas cover most practical electrical unit conversions:
From the power equation:
Many small devices list their voltage and current ratings on the label. The power consumption in watts is found by multiplying the two.
Example: Phone charger
A charger rated at 5V and 2A draws:
A 10W charger consumes 0.01 kWh for every hour it is plugged in and drawing current.
Example: Laptop power adapter
A laptop adapter rated at 19V and 3.42A draws:
Running for 4 hours per day uses approximately:
Appliances are often rated in amps, but energy consumption is measured in kilowatt-hours (kWh). The voltage of the local mains supply determines how many watts that current represents.
Example: Microwave oven
A microwave rated at 10A draws different wattages depending on the local supply voltage:
If the 1200W model runs for 30 minutes daily, it consumes 0.6 kWh per day, or 18 kWh per month. If the 2300W model runs for the same period, it consumes 1.15 kWh per day, or 34.5 kWh per month.
Energy suppliers charge by the kilowatt-hour (kWh), so converting watts to kilowatts is the first step in estimating energy consumption:
Example: Air conditioner
A 1500W air conditioner running for 8 hours per day uses:
Electrical systems use two types of current:
Most mains-powered devices contain an internal AC-to-DC converter. A laptop charger, for example, takes 120V or 230V AC from the wall and supplies 19V DC to the laptop. Electric vehicle chargers work similarly, converting AC grid power to the high-voltage DC used by the battery pack.
The table below shows watts converted to amps at both 120V and 230V for common appliance power ratings.
| Power (W) | Current at 120V (US/CA) | Current at 230V (UK/EU) |
|---|---|---|
| 100W | 0.83A | 0.43A |
| 500W | 4.17A | 2.17A |
| 1000W (1 kW) | 8.33A | 4.35A |
| 1500W | 12.5A | 6.52A |
| 2000W (2 kW) | 16.67A | 8.70A |
| 3000W (3 kW) | 25.0A | 13.04A |
Milliamps to amps conversion:
| Milliamps (mA) | Amps (A) |
|---|---|
| 100 mA | 0.1 A |
| 500 mA | 0.5 A |
| 1000 mA | 1.0 A |
| 2000 mA | 2.0 A |
For DC circuits, divide watts by volts:
For AC circuits, divide watts by voltage multiplied by power factor:
Example: A 60W light bulb on a 120V circuit draws 60 ÷ 120 = 0.5A. On a 230V circuit, the same 60W bulb draws 60 ÷ 230 = 0.26A.
For DC circuits, multiply amps by volts:
For AC circuits, multiply amps by voltage and power factor:
Example: A device drawing 5A on a 230V AC circuit with a power factor of 0.9 uses 5 × 230 × 0.9 = 1035W.
Power factor is the ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. It ranges from 0 to 1. Purely resistive loads such as incandescent bulbs and electric heaters have a power factor close to 1. Inductive loads such as motors and transformers typically have a lower power factor, meaning they draw more current than the wattage alone would suggest. For simple calculations involving resistive appliances, a power factor of 1 is a reasonable assumption.
Converting between watts, amps, and volts is useful for: