Watts to amps calculator
Convert watts to amps for DC, single-phase AC, and three-phase AC systems.
What this calculator covers
Use this calculator when you know the load power and need an estimated current draw at a given voltage.
This is especially useful for comparing equipment loads across different voltages or checking how much line current the same wattage would demand in single-phase versus three-phase service.
Frequently asked questions
- What is power factor and when does it matter?
- Power factor is a number between 0 and 1 that describes how efficiently an AC load converts electrical power into useful work. A purely resistive load like a heater has a power factor of 1, while motors and other inductive loads are typically lower. DC calculations ignore power factor entirely; for AC loads, entering an accurate power factor gives a more realistic current estimate.
- What formula does three-phase mode use?
- For three-phase AC, amps equal watts divided by (voltage times power factor times the square root of 3). The square root of 3 factor arises from the 120-degree phase relationship between the three legs of a balanced three-phase system.
- Why does the same wattage draw less current at higher voltage?
- Current is inversely proportional to voltage when power is fixed. A 1,800-watt load on 240 V draws half the current it would on 120 V, which is why higher-voltage circuits can carry larger loads with smaller conductors.
- Is this result suitable for sizing a circuit breaker?
- No. This calculation gives an estimated current draw under the stated conditions and simplified model. Actual circuit protection sizing must account for continuous-load rules, breaker trip curves, conductor ampacity, and local electrical code — consult a licensed electrician for installation decisions.
Tool
Run the calculation
Result
RESULT · AMPS
â„–197
Primary result
15.00 A
1,800.00 W at 120.00 V in AC single-phase mode draws about 15.00 A.
- Current
- 15.0000 A
- System type
- AC single-phase
- Power factor used
- 1.000
- Input power
- 1,800.00 W
Step-by-step solution
- 1.Choose the inverse power formula for the selected system type: I = W / (V x PF).
- 2.Use a power factor of 1.000.
- 3.Divide watts by the adjusted voltage term to solve for current.
Walkthrough
Visual walkthrough
Watts-to-amps reverses the usual power equation by dividing the load power by the voltage term that applies to the system type.
01
Start with the power load
1,800.00 W
Power is the numerator because current is the unknown being backed out from a known load.
02
Build the denominator
I = W / (V x PF)
Voltage is adjusted by power factor for AC loads, plus sqrt(3) for three-phase line-to-line systems.
03
Read the amperage
The result is the estimated line current for the selected simplified electrical model.
15.00 A