Amp Watts Calculator
Use this tool to convert between amps, watts, and volts for DC, single-phase AC, and three-phase AC systems.
- DC: W = V × A
- AC 1-Phase: W = V × A × PF
- AC 3-Phase: W = √3 × V × A × PF
How this amp watts calculator works
An amp watts calculator helps you quickly convert electrical current (amps) into electrical power (watts), or go the other direction when you already know watts and volts. This is useful for selecting equipment, checking circuit load, estimating energy use, and planning safe wiring decisions.
In practical terms, people use this kind of calculator when they ask questions like:
- How many watts does a 15 amp device use at 120V?
- How many amps will a 2000W heater draw on a 230V line?
- How does power factor affect AC motor loads?
Core formulas for amps, watts, and volts
1) DC power formula
For direct current systems, the relationship is straightforward:
Watts = Volts × Amps
From this, you can rearrange to find amps or volts:
- Amps = Watts ÷ Volts
- Volts = Watts ÷ Amps
2) AC single-phase power formula
In AC circuits, real power depends on power factor (PF):
Watts = Volts × Amps × Power Factor
If PF is not 1.0, watts are lower than simple volts-times-amps. This is common with motors, compressors, and inductive loads.
3) AC three-phase power formula
For balanced three-phase systems:
Watts = √3 × Volts × Amps × Power Factor
The √3 factor (about 1.732) is why three-phase systems transfer more power efficiently.
Step-by-step: using the calculator
- Select what you want to compute: watts, amps, or volts.
- Choose system type (DC, AC single-phase, or AC three-phase).
- Enter the known values in the fields.
- For AC, enter power factor (usually between 0.7 and 1.0 for many loads).
- Click Calculate to see the result and formula used.
Examples
Example A: Find watts from amps and volts (DC)
If a DC load uses 8A at 24V:
W = 24 × 8 = 192W
Example B: Find amps from watts and volts (single-phase AC)
Suppose an appliance is 1500W on a 120V line with PF = 0.95:
A = 1500 ÷ (120 × 0.95) = 13.16A
Example C: Find current in a 3-phase system
For 10,000W at 400V, PF = 0.9:
A = 10000 ÷ (√3 × 400 × 0.9) ≈ 16.04A
Quick reference table
| Voltage | Current | Approx. Watts (DC / PF=1) |
|---|---|---|
| 120V | 5A | 600W |
| 120V | 15A | 1800W |
| 230V | 10A | 2300W |
| 240V | 20A | 4800W |
| 400V (3-phase) | 16A | ≈11,085W at PF 1.0 |
Safety and planning notes
- Always size conductors and breakers according to local electrical code.
- Continuous loads are typically derated (for example, 80% rules in some regions).
- Starting current for motors can be much higher than running current.
- When in doubt, consult a licensed electrician or engineer.
FAQ
Is converting amps to watts always exact?
It is exact for DC with accurate voltage. For AC, accuracy depends on power factor and whether the load is balanced (for three-phase).
Can I use this for household appliances?
Yes. For many household loads, this calculator gives a practical estimate. Check appliance labels for rated watts, volts, and sometimes amps.
Why is my measured current different from calculated current?
Real systems have losses, voltage variation, harmonic distortion, and changing load behavior. Calculators provide a baseline, while meters show real-time conditions.