How do I convert watts to amps?

Divide watts by voltage (and by power factor for AC circuits). For a DC circuit: A = W ÷ V. For a single-phase AC circuit: A = W ÷ (V × PF). For a three-phase AC circuit: A = W ÷ (V × 1.732 × PF). For example, a 1,200-watt load on a 120V single-phase circuit with PF 0.85 draws 1,200 ÷ (120 × 0.85) = 11.76 amps.

What is power factor and why does it matter?

Power factor (PF) is the ratio of real power (watts) to apparent power (volt-amperes). It represents how efficiently current is converted to useful work. Purely resistive loads (heaters, incandescent bulbs) have PF = 1.0. Inductive loads (motors, transformers, compressors) typically have PF between 0.70 and 0.95. A lower power factor means the circuit draws more current for the same wattage, increasing conductor heating and electricity costs. Utilities often penalize commercial customers with consistently low PF.

How does three-phase differ from single-phase for watts-to-amps conversion?

Three-phase power distributes load across three conductors, with each conductor carrying current 120° out of phase with the others. The formula uses √3 (≈ 1.732) as a multiplier to account for this phase relationship: A = W ÷ (V × 1.732 × PF). This means a 10,000-watt three-phase load at 480V with PF 0.85 draws only 14.18 amps per phase — significantly less than a single-phase equivalent at 120V. Three-phase is preferred for large motors and commercial equipment because it delivers more power with smaller conductors.

What wire gauge do I need for a 1,500-watt load?

On a standard 120V single-phase circuit with PF 0.85, a 1,500-watt load draws 14.71 amps. The NEC continuous load rule requires ampacity ≥ load × 1.25, so you need a wire rated for at least 18.4 amps — 12 AWG copper (20A ampacity) is the correct choice. If the load is on a 240V circuit, current drops to 7.35 amps, and 14 AWG copper (15A ampacity) is sufficient. Always verify with a licensed electrician and your local AHJ.

kW (kilowatts) measures real power — the actual work done by the circuit, like heating, lighting, or running a motor. kVA (kilovolt-amperes) measures apparent power — the total current the circuit must supply, including reactive current that does no real work. The ratio of kW to kVA is the power factor. For DC circuits, kW and kVA are always equal because PF = 1.0. For AC circuits with inductive loads, kVA is always greater than kW. Utility companies and equipment ratings often specify kVA because that determines conductor and transformer sizing.

How do I convert amps to watts?

Multiply amps by voltage (and by power factor for AC). For DC: W = A × V. For single-phase AC: W = A × V × PF. For three-phase AC: W = A × V × 1.732 × PF. For example, a 20-amp three-phase circuit at 208V with PF 0.90 delivers 20 × 208 × 1.732 × 0.90 = 6,494 watts (about 6.5 kW). This reverse calculation is useful when reading a clamp meter and needing to know the load wattage.

How many watts can a 15-amp circuit handle?

A 15-amp circuit at 120V has a theoretical maximum of 15 × 120 = 1,800 watts. However, the NEC requires that continuous loads (those energized for 3 hours or more) not exceed 80% of circuit capacity: 0.80 × 1,800 = 1,440 watts maximum for continuous loads. As a practical rule, keep any single 15-amp circuit under 1,440 watts. For loads above that — space heaters, large appliances — use a 20-amp circuit (2,400W theoretical, 1,920W continuous) or a dedicated 240V circuit.

What is the difference between watts and amps?

Watts measure power — the rate at which energy is consumed or produced. Amps (amperes) measure current — the rate at which electrical charge flows through a conductor. Both are needed to describe a circuit: a 60-watt load at 120V draws 0.5 amps; the same 60 watts at 12V draws 5 amps. Watts = Volts × Amps (for DC). Higher voltage allows the same power to be delivered at lower current, which is why long-distance power transmission uses high-voltage lines — it minimizes current and thus resistive losses.

What is power factor?

Power factor (PF) is the ratio of real power (watts) to apparent power (volt-amperes, VA). A PF of 1.0 means all electrical energy drawn from the source is converted to useful work. A PF below 1.0 means some current is reactive — flowing back and forth without doing work (common in inductive loads like motors and transformers). For example, a 1,000W motor with PF 0.80 draws 1,000 ÷ (120 × 0.80) = 10.42 amps rather than 8.33 amps at unity PF. The extra current heats conductors without doing additional work, which is why utilities penalize commercial customers with low power factor.

Watts to Amps Calculator — DC, AC Single & 3-Phase

Converts watts to amps (or amps to watts) for DC, single-phase, and three-phase AC circuits, with kVA and wire gauge outputs.

How to Use This Watts to Amps Calculator

This watts to amps calculator converts between power and current for DC, single-phase, and three-phase AC circuits — select your conversion direction (Watts → Amps or Amps → Watts) — then enter your power or current value. Choose your current type (DC, AC Single-Phase, or AC Three-Phase) and select a voltage preset (12V, 24V, 120V, 240V, 480V) or enter a custom voltage. For AC circuits, set the power factor (default 0.85). The calculator instantly shows the converted value, kVA (AC only), kW equivalent, and a suggested wire gauge based on NEC continuous-load rules.

Circuit schematic: a source supplies voltage V. Current I (amps) flows through the switch to the load. Power P (watts) = V × I × PF for AC circuits.

Watts to Amps Formula

The formula depends on your circuit type:

DC circuits:A = W ÷ V — power factor is always 1.0, so no PF term is needed. Example: a 60-watt DC load at 12V draws 60 ÷ 12 = 5.00 amps.
AC single-phase:A = W ÷ (V × PF) — the power factor accounts for reactive current. At 120V and PF 0.85: 1,000 W draws 1,000 ÷ (120 × 0.85) = 9.80 amps.
AC three-phase:A = W ÷ (V × √3 × PF) — the √3 factor (≈ 1.732) accounts for the three-phase relationship. At 480V and PF 0.85: 10,000 W draws 10,000 ÷ (480 × 1.732 × 0.85) = 14.17 amps per phase.

To reverse the calculation (amps to watts), simply multiply: W = A × V × PF for single-phase, or W = A × V × √3 × PF for three-phase.

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DC vs. AC: Why the Formula Differs

In a DC circuit, current flows in one direction at a constant voltage. There is no phase difference between voltage and current, so all electrical energy is converted to real work — power factor is always 1.0. The conversion is a simple ratio: amps equals watts divided by volts.

In an AC circuit, voltage and current alternate in a sinusoidal wave. When a load is purely resistive (like a space heater), voltage and current stay in phase, giving PF = 1.0. But inductive loads (motors, transformers, compressors) cause current to lag behind voltage, creating reactive power that does no work but still heats the conductors. The power factor represents how much of the apparent current (amperes) is converted to real power (watts). A PF of 0.85 means 85% efficiency — for every 100 VA drawn from the supply, only 85 W does useful work.

Power Factor in AC Circuits

Power factor ranges from 0 to 1.0. Most residential loads have PF above 0.85; motors under partial load can dip to 0.70 or lower. Here are typical values for common loads:

Resistive loads (heaters, incandescent bulbs): PF = 1.0
LED drivers and switch-mode supplies: PF = 0.90–0.99 (with PFC)
Induction motors at full load: PF = 0.85–0.95
Induction motors at half load: PF = 0.70–0.85
Fluorescent lights (magnetic ballast): PF = 0.50–0.70

If you do not know your load's power factor, use 0.85 as a conservative default for general AC motor loads. For purely resistive loads (electric resistance heaters, toasters), use 1.0. Always check the equipment nameplate when precise values are needed.

Three-Phase Watts to Amps

Three-phase power is standard in commercial and industrial settings. Three conductors each carry alternating current 120° out of phase with each other, which allows balanced loads to cancel each other's return current. The √3 factor in the formula emerges from the geometry of this phase relationship.

For example, a 480V three-phase 15 HP motor (approximately 11,185 watts) at PF 0.88 draws:

A = 11,185 ÷ (480 × 1.732 × 0.88) = 15.30 amps per phase

This is the line current — the current flowing in each of the three phase conductors. Three-phase systems deliver more power per conductor than single-phase at the same voltage, which is why large motors, HVAC equipment, and industrial machinery are almost always three-phase.

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Wire Sizing for Your Load

Once you know the load current in amps, use NEC Table 310.16 to select the correct copper wire gauge. The NEC continuous-load rule (NEC 210.19(A)(1)) requires that conductors be rated for at least 125% of continuous load current — loads that operate for 3 hours or more are considered continuous. This calculator applies the 125% factor automatically to suggest a wire gauge.

Common AWG ratings for copper conductors at 60°C:

14 AWG — 15A (rated) → 12A continuous max
12 AWG — 20A (rated) → 16A continuous max
10 AWG — 30A (rated) → 24A continuous max
8 AWG — 40A (rated) → 32A continuous max
6 AWG — 55A (rated) → 44A continuous max

For a more detailed wire sizing analysis including voltage drop over long runs, use our wire size calculator. For voltage drop specifically, see our voltage drop calculator.

Electrical Safety Disclaimer

This calculator provides estimates for informational purposes only and is not a substitute for the advice of a licensed electrician or electrical engineer. Formulas are based on standard NEC methodology (NEC 310.15, 210.19) and assume ideal conditions — actual current draw depends on load characteristics, ambient temperature, installation method, conductor bundling, and local code amendments. Wire gauge suggestions are a starting point only; breaker sizing, conduit fill, derating factors, and termination temperature ratings must also be considered. Always have electrical work designed, installed, and inspected by a licensed professional and your local Authority Having Jurisdiction (AHJ).

Sources & References

NFPA 70: National Electrical Code (NEC) 2023 Edition — National Fire Protection Association

Watts to Amps Calculator

DC Formula

AC Formulas

Common Wattages