Watts to Amps Calculator (AC & DC)

Convert watts to amps for DC, single‑phase AC, and three‑phase AC circuits. Adjust voltage and power factor, see formulas, and get instant results.

Watts to Amps Converter

Circuit type

Enter real power (watts). For kW, the calculator will convert automatically.

Use line‑to‑line voltage for three‑phase systems (e.g. 400 V, 480 V).

Typical values: 1.0 (heaters), 0.9 (electronics), 0.8 (motors). DC effectively has PF = 1.

Quick presets

How to convert watts to amps

Watts (W) measure power. Amps (A) measure current. To convert watts to amps you need to know the voltage and, for AC circuits, the power factor and whether the system is single‑phase or three‑phase.

Formulas

DC circuits

For direct current (DC):

\[ I = \frac{P}{V} \]

  • \(I\) = current in amperes (A)
  • \(P\) = power in watts (W)
  • \(V\) = voltage in volts (V)

Single‑phase AC

For single‑phase AC circuits:

\[ I = \frac{P}{V \times \text{PF}} \]

  • \(\text{PF}\) = power factor (0–1)

Three‑phase AC

For three‑phase AC circuits (using line‑to‑line voltage):

\[ I = \frac{P}{\sqrt{3} \times V \times \text{PF}} \]

where \(\sqrt{3} \approx 1.732\).

Step‑by‑step example (single‑phase AC)

Suppose you have a 1500 W space heater on a 120 V single‑phase circuit with power factor 1.0:

  1. Identify the formula: \(I = \dfrac{P}{V \times \text{PF}}\).
  2. Plug in the values: \(I = \dfrac{1500}{120 \times 1.0}\).
  3. Compute: \(I = \dfrac{1500}{120} = 12.5\ \text{A}\).

The heater draws about 12.5 amps.

Step‑by‑step example (three‑phase AC)

A 5 kW three‑phase motor is supplied at 400 V line‑to‑line with power factor 0.8:

  1. Use the three‑phase formula: \[ I = \frac{P}{\sqrt{3} \times V \times \text{PF}} \]
  2. Insert values: \[ I = \frac{5000}{1.732 \times 400 \times 0.8} \]
  3. Calculate the denominator: \[ 1.732 \times 400 \times 0.8 \approx 554.2 \]
  4. Compute current: \[ I \approx \frac{5000}{554.2} \approx 9.0\ \text{A} \]

The motor current is about 9 amps per phase.

Typical power factor values

Power factor depends on the type of load. If you don’t know it, these rules of thumb are often used for estimation:

  • 1.0 – resistive loads (heaters, incandescent lamps)
  • 0.9 – computers, phone chargers, LED drivers with PFC
  • 0.8 – small induction motors, older fluorescent lighting

Always check the equipment nameplate or datasheet for accurate values when available.

Watts, volts, and amps: quick intuition

  • Voltage (V) is like pressure pushing electrons.
  • Current (A) is the flow rate of electrons.
  • Power (W) is how fast electrical energy is being used or delivered.

For a given power, higher voltage means lower current, and lower voltage means higher current. That’s why high‑power equipment is often run at higher voltages: to keep current (and cable size and losses) down.

Safety note

This calculator is for educational and planning purposes only. It does not replace electrical codes or professional design. For breaker sizing, conductor selection, and protective devices, always follow your local electrical regulations (such as NEC, IEC, or BS 7671) and consult a qualified electrician or engineer.

Frequently asked questions

Can I convert amps back to watts?

Yes. The inverse formulas are:

  • DC: \(P = V \times I\)
  • Single‑phase AC: \(P = V \times I \times \text{PF}\)
  • Three‑phase AC: \(P = \sqrt{3} \times V \times I \times \text{PF}\)

Use the “Swap: Amps → Watts” button in the calculator to switch direction.

What’s the difference between kW and W in the calculator?

1 kilowatt (kW) = 1000 watts (W). The calculator automatically converts kW to W internally, so you can enter whichever is more convenient.