Amps to Watts Calculator
Converting amps to watts requires knowing the voltage and, for AC circuits, the power factor. This calculator handles three circuit types: DC (direct current), AC single-phase, and AC three-phase. For DC and resistive AC loads with a power factor of 1.0, the formula is simply watts = amps times volts. For AC circuits with inductive or capacitive loads such as motors and transformers, the power factor is less than 1.0, meaning the circuit draws more current than a purely resistive load of the same wattage. For three-phase systems, the line-to-line voltage and the square root of 3 (approximately 1.732) are used. Enter the current in amps, the voltage, the power factor (default 1.0), and select the circuit type. The result shows real power in watts and kilowatts. Common applications include sizing generators and inverters, checking that a circuit can handle a load, and comparing the power consumption of equipment with different voltage and current ratings.
Amps to watts formulas
DC: W = A × V
AC Single-phase: W = A × V × PF
AC Three-phase: W = A × VLL × 1.732 × PF
Worked examples
- DC: 10 A at 12 V = 10 × 12 = 120 W
- AC single-phase: 10 A at 120 V, PF 0.95 = 10 × 120 × 0.95 = 1,140 W
- AC three-phase: 10 A at 208 V, PF 0.85 = 10 × 208 × 1.732 × 0.85 = 3,063 W
Frequently asked questions
What is the difference between amps and watts?
Amps (amperes) measure electric current, which is the rate of flow of electric charge through a conductor. Watts measure electric power, which is the rate at which energy is transferred or consumed. In a simple DC circuit, the relationship is W = A x V. In AC circuits, the power factor also plays a role. Knowing the wattage tells you how much energy the device uses per unit time, which is what determines your electricity bill. Knowing the current tells you how to size wires, breakers, and other protective devices.
Why does power factor matter for AC circuits?
In AC circuits, voltage and current are not always perfectly in phase with each other, especially when the load includes inductors (motors, transformers) or capacitors. Power factor (PF) is a number between 0 and 1 that represents the fraction of apparent power (kVA) that does actual work (real power, kW). A motor with PF 0.85 draws 18% more current than a purely resistive load of the same wattage. Residential loads are typically close to PF 1.0, but industrial motor loads are often 0.8 to 0.9.
What does the 1.732 factor mean in three-phase calculations?
The factor 1.732 is the square root of 3 (approximately 1.7321). In a balanced three-phase system, the relationship between line-to-line voltage and line-to-neutral voltage involves this factor. When calculating three-phase power from line-to-line voltage and line current, the formula P = V x I x sqrt(3) x PF accounts for the geometry of the three-phase system. The three phases offset by 120 degrees produce this mathematical constant.
What are typical household and industrial voltages?
In the US, standard single-phase household voltage is 120V for general outlets and 240V for large appliances (dryers, ranges, water heaters, air conditioners). Standard three-phase industrial voltages include 208V (from a 120/208V wye system), 240V (from a delta system), and 480V (from a 277/480V wye system used in commercial and industrial buildings). Always confirm the voltage at the point of connection before selecting equipment.
How do I find an appliance's current from its nameplate?
Most appliances list rated current (amps) directly on their nameplate label. If only watts and voltage are shown, divide watts by voltage (and by power factor for AC motors) to get amps. For example, a 1,200W appliance on 120V at PF 1.0 draws 10A. Motor nameplates typically show full-load amperage (FLA), which is the current at rated load and voltage. The FLA is what you use to size the branch circuit breaker and wiring per NEC Article 430.
Sources
- IEEE Standard 141-1993 (Red Book), Electric Power Distribution for Industrial Plants: standards.ieee.org.
- NFPA 70: National Electrical Code 2023: nfpa.org.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only.