Based on W = V × A. Enter any two values to calculate the third — or choose a mode below to treat one value as the primary input. For AC loads with power factor (PF), this simple version may be inaccurate.
Interactive Calculator (Cron-style options layout)
Quick Formulas
Note: for AC systems, real power is often P = V × A × PF (power factor).
Quick Reference (Common US Voltages)
| Volts (V) | Amps (A) | Watts (W) |
|---|---|---|
| 120 | 5 | 600 |
| 120 | 10 | 1200 |
| 120 | 15 | 1800 |
| 240 | 10 | 2400 |
| 240 | 30 | 7200 |
Tip: 120V × 15A ≈ 1800W is a common “standard outlet” mental shortcut in the US.
Real-World Examples
- A 120V, 10A device uses about 1200W.
- A 1500W space heater on 120V draws about 12.5A (1500 ÷ 120).
- A 3000W load at 240V draws about 12.5A (3000 ÷ 240).
Common Mistakes
Watch out for AC power factor: many motors and some electronics don’t have PF = 1, so “V × A” can overestimate real watts.
FAQ
Can I find watts if I know volts and amps? Yes: W = V × A.
What if I only know one value? You need at least two (unless you assume something like resistance or PF).
Does this work for AC? It’s a good estimate for resistive loads; for many AC loads you need power factor (PF).