Amps to Watts Conversion Calculator

Enter the current and voltage to convert amps to watts for DC and AC single and three-phase circuits.

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How to Convert Amps to Watts

Converting amps to watts can be done using the Watt’s Law power formula, which states that I = P ÷ V, where P is the power measured in watts, I is the current measured in amps, and V is the voltage measured in volts.

Amps to Watts Formula

Multiplying each side of the equation by the voltage V, it is possible to express the amps to watts formula as:[1]

P(W) = I(A) × V(V)

Thus, the power P in watts is equal to the current I in amps multiplied by the voltage V in volts.

Power formula triangle showing the formula to convert amps to watts, which states that the power in watts are equal to the current in amps times the voltage in volts

How Many Watts Are in an Amp?

Using the formula above, you can also figure out how many watts of power there are in one amp, depending on the circuit voltage. For example, at 120 volts, 120 watts of power are consumed at 1 amp, and 240 watts are consumed at 2 amps.

Likewise, at 240 volts, 240 watts of power are consumed at 1 amp, and 480 watts are consumed at 2 amps.

Example: 15 Amps to Watts

For example, let’s calculate the wattage capacity of a 15-amp, 120-volt electrical circuit.

P(W) = 15 A × 120 V
P(W) = 1,800 W

So, 15 amps of current at 120 volts will generate 1,800 watts of power.

Conversion for Single-Phase AC Circuits

Converting amps to watts for a single-phase AC circuit with a power factor requires a slight variation of the formula.

P(W) = I(A) × V(V) × PF

The power P in watts is equal to the current I in amps multiplied by the voltage V in volts multiplied by the power factor PF.

AC electrical power is composed of a real part expressed in watts and a reactive part expressed in volt-amps. The magnitude of both real and reactive together is called the apparent power, and the PF gives the ratio of real power to apparent power.[2]

The power factor is determined by the alternating current frequency and the inductive or capacitive elements in the circuit.

If you’re trying to calculate PF from power, current, and voltage, we suggest using a power factor calculator to find the PF value.

Conversion for Three-Phase AC Circuits

The formulas to convert amps to watts for three-phase AC circuits are a bit different from the formulas above.

Using Line to Line Voltage

For three-phase AC circuits where the current, line to line RMS voltage, and power factor are known, the formula to convert amps to watts is:

P(W) = I(A) × VL-L(V) × PF × √3

The power P in watts is equal to the current I in amps multiplied by the voltage V in volts multiplied by the power factor PF multiplied by the square root of 3.

This equation calculates the power for one pair of wires in a three-phase system, but you’ll need to multiply it by three when considering all three pairs of wires in a three-phase system.

Using Line to Neutral Voltage

For three-phase AC circuits where the current, line to neutral RMS voltage, and power factor are known, the formula to convert amps to watts is:

P(W) = I(A) × VL-N(V) × PF × 3

The power P in watts is equal to the current I in amps multiplied by the voltage V in volts multiplied by the power factor PF multiplied by 3.

This formula calculates the power delivered by all three wires in a three-phase system, but you’ll need to divide by three if you’re considering a single wire in the three-phase system.

How to Convert Amps and Ohms to Watts

You can also convert amps to watts using circuit resistance with this formula:[1]

P(W) = I(A)2 × R(Ω)

The power P in watts is equal to the current I in amps squared multiplied by the resistance R in ohms.

Since 1 kilowatt is equal to 1,000 watts, it is possible to use the formulas above to also convert amps to kW, but the result will need to be divided by 1,000. You can also use our amps to kW calculator to solve for kilowatts.

Table: Amps to Watts at 120V & 240V AC

Table showing amps converted to watts at 120 and 240 volts AC for common appliances and circuit sizes.
Current (Amps) Power (Watts) Voltage (Volts)
1 amp 120 watts 120 volts
2 amps 240 watts 120 volts
3 amps 360 watts 120 volts
4 amps 480 watts 120 volts
5 amps 600 watts 120 volts
6 amps 720 watts 120 volts
7 amps 840 watts 120 volts
8 amps 960 watts 120 volts
9 amps 1,080 watts 120 volts
10 amps 1,200 watts 120 volts
11 amps 1,320 watts 120 volts
12 amps 1,440 watts 120 volts
13 amps 1,560 watts 120 volts
14 amps 1,680 watts 120 volts
15 amps 1,800 watts 120 volts
20 amps 2,400 watts 120 volts
25 amps 3,000 watts 120 volts
30 amps 3,600 watts 120 volts
15 amps 3,600 watts 240 volts
20 amps 4,800 watts 240 volts
30 amps 7,200 watts 240 volts
40 amps 9,600 watts 240 volts
50 amps 12,000 watts 240 volts
60 amps 14,400 watts 240 volts
70 amps 16,800 watts 240 volts
80 amps 19,200 watts 240 volts
90 amps 21,600 watts 240 volts
100 amps 24,000 watts 240 volts
125 amps 30,000 watts 240 volts
150 amps 36,000 watts 240 volts
200 amps 48,000 watts 240 volts

Table: Amps to Watts at 12V DC

Table showing amps converted to watts at 12 volts DC.
Current (Amps) Power (Watts) Voltage (Volts)
1 amp 12 watts 12 volts
2 amps 24 watts 12 volts
3 amps 36 watts 12 volts
4 amps 48 watts 12 volts
5 amps 60 watts 12 volts
6 amps 72 watts 12 volts
7 amps 84 watts 12 volts
8 amps 96 watts 12 volts
9 amps 108 watts 12 volts
10 amps 120 watts 12 volts
11 amps 132 watts 12 volts
12 amps 144 watts 12 volts
13 amps 156 watts 12 volts
14 amps 168 watts 12 volts
15 amps 180 watts 12 volts
20 amps 240 watts 12 volts
30 amps 360 watts 12 volts
40 amps 480 watts 12 volts
50 amps 600 watts 12 volts
60 amps 720 watts 12 volts
70 amps 840 watts 12 volts
80 amps 960 watts 12 volts
90 amps 1,080 watts 12 volts
100 amps 1,200 watts 12 volts

You might also be interested in our watts to amps calculator.

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References

  1. Miller, C., NFPA's Electrical References, National Fire Protection Association, 2004, Jones & Bartlett Learning, 67-75. https://www.google.com/books/edition/NFPA_s_Electrical_References/raUyIi7i-asC
  2. Fiore, J., AC Electrical Circuit Analysis - A Practical Approach, 2022, 274. http://www.dissidents.com/resources/ACElectricalCircuitAnalysis.pdf