Amps to Watts Calculator
Quick explanation
Use this calculator to estimate wattage when you know current and voltage. For deeper formula checks, visit the Ohm's Law calculator. New to the fundamentals? See Electricity Basics or read the full how to convert amps to watts guide.
Estimated power: 1800 W
How to convert amps to watts
To convert amps to watts, you need both current and voltage. Amps measure electrical flow; watts measure power, the rate at which energy is used. Voltage is the bridge between them.
The formula W = A × V works for most practical planning purposes with resistive loads (heaters, lighting, simple appliances). For motor-driven equipment and electronics, actual power can differ due to power factor and startup behavior, so treat the result as a planning estimate.
This calculation is most useful when you know a device's current rating from its nameplate or a clamp meter reading, and you want to estimate total circuit load in watts for comparison against breaker capacity or an energy estimate.
How to convert
Core conversion formula
Power in watts equals current in amps multiplied by voltage in volts.
W = A × V
watts = amps × volts
Inverse relationship
If you already know watts and voltage and need amps, reverse the formula.
A = W / V
Worked examples
Question: How many watts does a 15A circuit at 120V supply?
Solution: W = 15 × 120 = 1800 W
Question: How many watts is 10A at 240V?
Solution: W = 10 × 240 = 2400 W
Question: How many watts is 2A at 12V (DC system)?
Solution: W = 2 × 12 = 24 W
Common mistakes and notes
- Amps and voltage must match the same system; do not mix 120V and 240V values in one calculation.
- For motor loads, actual power draw may be higher than this estimate due to power factor.
- Nameplate current ratings reflect steady-state draw; startup surges can be significantly higher.
- Use this as a planning check, then verify circuit capacity against breaker rating and applicable code.
Assumptions
- Single-phase simplified estimate unless otherwise specified.
- Input values are nominal; real-world equipment can vary.
- Results are planning guidance only, not code certification.
Worked example
Example: 15 A at 120 V = 1,800 W.
FAQ
How do you convert amps to watts?
Multiply amps by volts: W = A × V. You need both values because amps alone do not tell you power.
How many watts is 15 amps at 120 volts?
15 × 120 = 1800 W. This is the theoretical maximum for a standard 15A North American branch circuit.
Can I use this for breaker sizing?
Use it as a quick estimate only, then verify against the continuous load guideline (80% of breaker rating for sustained loads) and local code requirements.
Why can actual wattage differ from this estimate?
Real systems vary with power factor (especially motors and electronics), voltage fluctuations, and startup surges. Use the result as a planning check, not a precise measurement.
What is the difference between amps to watts and watts to amps?
Amps to watts tells you the power a device uses given its current draw and voltage. Watts to amps tells you the current a device will draw given its power rating and voltage. Both use the same formula W = A × V, just solved in different directions.
Related calculators
⚠️ Sanity Check Only
This tool provides informational estimates only. It is not professional engineering advice. Electrical work is dangerous and governed by strict local codes.
Before you start:
- Verify these results with a licensed electrician.
- Cross-reference with the latest Electrical Code (NEC/CEC).
- Never work on live circuits.