Watts to Amps Calculator
Converting watts to amps is essential for circuit breaker sizing, wire gauge selection, and load analysis. This calculator supports DC circuits, AC single-phase circuits, and AC three-phase circuits. For DC: amps = watts divided by volts. For AC single-phase: amps = watts divided by (volts times power factor). For AC three-phase: amps = watts divided by (volts times 1.732 times power factor). The power factor represents how efficiently the electrical power is converted to useful work. Resistive loads like electric heaters and incandescent bulbs have a power factor of 1.0. Inductive loads like motors and transformers typically have a power factor between 0.8 and 0.95. Enter the power in watts, the voltage, and the power factor to get the current in amps. The result can be used to select the correct wire gauge from the AWG ampacity table or to determine circuit breaker size per NEC requirements.
Watts to amps formulas
DC: A = W / V
AC Single-phase: A = W / (V × PF)
AC Three-phase: A = W / (VLL × 1.732 × PF)
Worked examples
- DC: 1,200 W at 12 V = 1,200 / 12 = 100.00 A
- AC single-phase: 1,200 W at 120 V, PF 1.0 = 1,200 / (120 × 1.0) = 10.00 A
- AC three-phase: 10,000 W at 208 V, PF 0.85 = 10,000 / (208 × 1.732 × 0.85) = 32.70 A
NEC breaker sizing for continuous loads
Per NEC Article 210.20(A), a continuous load (operating 3 hours or more) must not exceed 80% of the breaker rating, meaning the breaker must be rated at least 125% of the load current. For 10A continuous load, minimum breaker = 10 × 1.25 = 12.5A, so round up to the next standard size of 15A.
Frequently asked questions
Why do amps matter for circuit sizing?
Circuit breakers, fuses, and wire gauges are all rated in amps. When you know the wattage of a load, converting to amps tells you whether the existing circuit can handle it and what size breaker or wire is needed for a new circuit. The NEC requires that the ampacity of a circuit conductor equal or exceed the load current, and that continuous loads (running for 3 hours or more) be limited to 80% of the circuit breaker rating.
How does power factor change the current drawn?
A lower power factor means a load draws more current from the supply for the same amount of real work done. For example, a 1,000W load at PF 1.0 on 120V draws 8.33A. The same 1,000W load at PF 0.80 draws 10.42A, or about 25% more current. This extra current still flows through the wires and breaker, increasing heat and losses, which is why utilities and the NEC care about power factor correction for large inductive loads.
Why does three-phase draw less current than single-phase for the same power?
Three-phase power distributes the load across three conductors simultaneously. For the same real power output, the current in each phase of a three-phase system is lower than in a single-phase system, because the sqrt(3) factor in the three-phase formula means more power is delivered per amp. This is one reason large industrial loads are powered three-phase: smaller conductors are needed for the same delivered power, reducing material cost and resistive losses.
How do I size a breaker from watts?
Convert watts to amps using the appropriate formula, then apply NEC Article 210.20 sizing rules. For continuous loads (operating for 3 hours or more), the NEC requires the breaker to be rated at least 125% of the load current. For non-continuous loads, the breaker must be rated at least 100% of the load current. Always round up to the next standard breaker size (15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200A, etc.). Consult a licensed electrician for final sizing.
What are typical household current levels?
Standard US household outlets are rated 15A at 120V (on a 15A breaker) or 20A at 120V (on a 20A breaker). Large appliances typically use 240V circuits: electric dryers typically draw 22-30A, electric ranges 40-50A, central air conditioners 15-60A depending on size, and electric water heaters 18-30A. The total service entrance for a typical US home is 100-200A at 240V split-phase.
Sources
- NFPA 70: National Electrical Code (NEC) 2023, Articles 210, 215, 430: nfpa.org.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. For reference only. Consult a licensed electrician for installation decisions. See our methodology.