Calculator
How to convert amps to watts
Converting amps (A) to watts (W) is one of the most common electrical calculations for home projects, solar systems, battery setups, and appliance sizing. Watts tell you real power usage, while amps tell you current flow. To convert correctly, you also need voltage and, for many AC systems, power factor.
Core formulas
AC Single-Phase: W = A × V × PF
AC Three-Phase: W = √3 × A × V × PF
Where:
- W = power in watts
- A = current in amps
- V = voltage in volts
- PF = power factor (between 0 and 1)
Why voltage matters
Amps alone are not enough to determine power. For example, 10A at 12V is only 120W, while 10A at 240V is 2,400W. Same current, very different power. That is why this calculator always asks for voltage.
Step-by-step examples
Example 1: DC circuit
If your DC load pulls 5A at 24V:
Example 2: AC single-phase appliance
If a device draws 8A at 120V with a power factor of 0.9:
Example 3: AC three-phase motor
If a motor draws 15A at 400V with PF 0.85:
Quick reference table
| System | Formula | When to use |
|---|---|---|
| DC | W = A × V | Batteries, automotive, many solar/battery circuits |
| AC Single-Phase | W = A × V × PF | Most household appliances and outlets |
| AC Three-Phase | W = √3 × A × V × PF | Industrial motors, large HVAC, commercial loads |
Common mistakes to avoid
- Ignoring power factor: This can overestimate real watts in AC systems.
- Using the wrong system type: Three-phase and single-phase formulas are not interchangeable.
- Mixing line and phase voltage: Especially important in three-phase calculations.
- Confusing watts and watt-hours: Watts are power, watt-hours are energy over time.
FAQ
Can I calculate watts from amps without volts?
No. You need voltage to convert amps to watts.
What power factor should I use?
If you do not know the exact PF, use the manufacturer specification. For purely resistive loads (such as many heaters), PF is often close to 1.0.
How do I convert watts back to amps?
Rearrange the formulas:
- DC: A = W ÷ V
- AC single-phase: A = W ÷ (V × PF)
- AC three-phase: A = W ÷ (√3 × V × PF)
Final takeaway
For a reliable amps-to-watts conversion, always identify your electrical system first, then include voltage and (for AC) power factor. Use the calculator above to quickly get accurate watt values for planning circuits, choosing components, or estimating equipment loads.