Ohm Calculator
Instant electrical conversions & energy cost estimates.
Enter any two values and the rest fill in automatically.
Watts equal amps times volts, so turning a current reading into power is simply a matter of multiplying by the circuit's voltage — the guide, charts, and breaker limits below cover every common case.
How to Convert Amps to Watts (P = I × V)
Watts measure power while amps measure current, so to turn a current reading into power you also need the voltage — power equals current times voltage. In symbols, P = I × V, where P is power in watts, I is current in amps, and V is voltage in volts.
- Find the current (I) in amps — from the appliance label, a clamp meter, or the circuit's breaker rating.
- Identify the voltage (V) — 120 V for standard US outlets, 230–240 V for large appliances and most of Europe, or 12 V for automotive and solar systems.
- Multiply amps by volts — the result is power in watts. Example: 10 A × 120 V = 1,200 W.
Working in milliamps (mA)? Small electronics are often rated in milliamps. Divide the milliamp figure by 1,000 to get amps first, then multiply by the voltage — for example, 500 mA at 5 V is 0.5 A × 5 V = 2.5 W.
Working the other way? If you already know your power draw, use our Watts to Amps calculator to find the current instead.
Why Use an Amps to Watts Calculator?
Converting current to power by hand is easy to get wrong when it matters most. A calculator removes the guesswork in situations like these:
- Sizing solar inverters and batteries. Off-grid gear is rated in watts, but panels and charge controllers are specified in amps at 12 V or 24 V — converting keeps components matched and within their limits.
- Checking circuit-breaker limits. Breakers trip on amps while appliances are labelled in watts; converting confirms whether a heater or power tool fits a 15 A or 20 A circuit before you plug it in.
- Electronics and hobbyist projects. When wiring LEDs, motors, or microcontrollers, turning current draw into watts helps you choose the right power supply and component ratings.
- Estimating running costs. Utilities bill in kilowatt-hours, so converting an appliance's amp draw into watts is the first step toward knowing what it costs to run.
Common Amps to Watts Conversion Charts
Because watts depend on voltage, the same current produces very different power at different voltages. These charts convert common amp ratings to watts at three everyday voltages.
| Amps | Watts |
|---|---|
| 1 A | 120 W |
| 5 A | 600 W |
| 10 A | 1,200 W |
| 15 A | 1,800 W |
| 20 A | 2,400 W |
| 30 A | 3,600 W |
| 50 A | 6,000 W |
| Amps | Watts |
|---|---|
| 1 A | 240 W |
| 5 A | 1,200 W |
| 10 A | 2,400 W |
| 15 A | 3,600 W |
| 20 A | 4,800 W |
| 30 A | 7,200 W |
| 50 A | 12,000 W |
| Amps | Watts |
|---|---|
| 1 A | 12 W |
| 5 A | 60 W |
| 10 A | 120 W |
| 15 A | 180 W |
| 20 A | 240 W |
| 30 A | 360 W |
| 50 A | 600 W |
Quick Conversions & Breaker Limits
Convert 15 Amps to Watts
On a standard 120 V US circuit, 15 amps equals 15 × 120 = 1,800 watts. The National Electrical Code limits continuous loads (three hours or more) to 80% of the breaker rating, so the safe sustained maximum is about 1,440 watts. That headroom is why a single 1,500 W space heater can trip a 15 A breaker once other devices share the circuit — see our full 15-amp circuit guide for what you can safely run.
Convert 20 Amps to Watts
A 20 A circuit at 120 V provides 20 × 120 = 2,400 watts, with an 80% continuous limit of 1,920 watts. Kitchens, garages, and workshops are commonly wired for 20 A precisely because appliances such as microwaves, toasters, and power tools draw more than a 15 A circuit can safely supply — our 20-amp circuit guide breaks down these heavier loads.
Frequently Asked Questions
What is Ohm's Law? +
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, expressed as V = I × R (Voltage = Current × Resistance). It's the foundation for calculating power, where Watts = Amps × Volts.
How do I convert watts to kilowatts? +
Divide the number of watts by 1,000. For example, 2,500 watts equals 2.5 kilowatts. Kilowatts are typically used to describe larger loads and to measure energy consumption on your utility bill.
How is my electricity bill calculated? +
Utilities charge per kilowatt-hour (kWh). Multiply an appliance's power in kilowatts by the hours it runs to get kWh consumed, then multiply by your electricity rate. The Energy Cost tab above does this automatically for daily, monthly, and yearly estimates.
What is a kilowatt-hour (kWh)? +
A kilowatt-hour is a unit of energy equal to running a 1,000-watt appliance for one hour. It is the standard unit used by energy providers to measure and bill electricity usage.