Watts to Amps Conversion Calculator

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

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How to Convert Watts to Amps

Converting watts to amps can be done using the Watt’s Law power formula, which states that the current is equal to the power divided by the voltage.

Watts to Amps Formula

Using Watt’s Law, you can find amps given power and voltage using the following formula:[1]

I(A) = P(W) / V(V)

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

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How Many Amps Are in a Watt?

Using the formula above, you can also calculate how many amps of current are drawn for each watt of power, depending on the circuit voltage. For example, at 120 volts, 0.008333 amps of current are drawn to generate 1 watt of power, and 0.8333 amps are drawn to generate 100 watts.

At 240 volts, 0.004167 amps of current are drawn to generate 1 watt of power, and 0.4167 amps are drawn to generate 100 watts.

Example: 1,500 Watts to Amps at 120V

For example, let’s calculate the current draw, or amperage, of a 1,500-watt microwave at 120 volts.

I(A) = 1,500 W ÷ 120 V
I(A) = 12.5 A

So, a 1,500-watt microwave will draw 12.5 amps of current at 120 volts.

Example: 2,000 Watts to Amps at 240V

For example, let’s calculate the current draw of a 2,000-watt electric heater at 240 volts.

I(A) = 2,000 W ÷ 240 V
I(A) = 8.33 A

So, a 2,000-watt heater will draw 8.33 amps of current at 240 volts.

Conversion for Single-Phase AC Circuits

Computing power from current for a single-phase AC circuit with a power factor uses a slightly different formula.

I(A) = P(W) / V(V) × PF

In other words, the current I in amps is equal to the power P in watts divided by the product of the voltage V in volts and the power factor PF. If you want to learn more about calculating power factor, try our power factor calculator.

Conversion for Three-Phase AC Circuits

The formulas to convert watts to amps for three-phase AC circuits are a bit different from the single-phase and DC formulas. Use the formulas below for line-to-line or line-to-neutral RMS voltages in a three-phase circuit.

Using Line-to-Line Voltage

For three-phase AC circuits where the line-to-line voltage is known, the formula to convert watts to amps is:[1][2]

I(A) = P(W) / VL-L(V) × PF × √3

The current I in amps is equal to the power P in watts divided by the product of the line-to-line voltage V in volts, the power factor PF, and the square root of 3.

Note that this formula measures the current draw for a single pair of wires in a three-phase system; to calculate the current for all three pairs, you need to multiply the result by three.

Using Line-to-Neutral Voltage

For three-phase AC circuits where the line-to-neutral voltage is known, the formula to convert watts to amps is:

I(A) = P(W) / VL-N(V) × PF × 3

The current I in amps is equal to the power P in watts divided by the product of line-to-neutral voltage V in volts, the power factor PF, and 3.

This formula calculates the current for all three wires in a three-phase system; to find the current for a single wire, you’ll need to divide the result by three.

How to Convert Watts and Ohms to Amps

It is also possible to convert watts to amps if the resistance of a simple resistive circuit is known by using this formula:[1]

I(A) = √(P(W) ÷ R(Ω))

The current I in amps is equal to the square root of the power P in watts divided by the resistance R in ohms.

It is not possible to convert watts directly to amps without also knowing voltage or resistance.

Because 1 kilowatt is equal to 1,000 watts, it is also possible to use the formulas above to convert kW to amps, but watts need to be converted to kW first. Use our kW to amps calculator to solve using kilowatts.

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

Table showing watts converted to amps at 120 and 240 volts AC.
Power (Watts) Current (Amps) Voltage (Volts)
50 watts 0.4167 amps 120 volts
100 watts 0.8333 amps 120 volts
150 watts 1.25 amps 120 volts
200 watts 1.667 amps 120 volts
250 watts 2.083 amps 120 volts
300 watts 2.5 amps 120 volts
350 watts 2.917 amps 120 volts
400 watts 3.333 amps 120 volts
450 watts 3.75 amps 120 volts
500 watts 4.167 amps 120 volts
600 watts 5 amps 120 volts
700 watts 5.833 amps 120 volts
800 watts 6.667 amps 120 volts
900 watts 7.5 amps 120 volts
1,000 watts 8.333 amps 120 volts
1,100 watts 9.167 amps 120 volts
1,200 watts 10 amps 120 volts
1,300 watts 10.833 amps 120 volts
1,400 watts 11.667 amps 120 volts
1,500 watts 12.5 amps 120 volts
1,600 watts 13.333 amps 120 volts
1,700 watts 14.167 amps 120 volts
1,800 watts 15 amps 120 volts
2,400 watts 20 amps 120 volts
3,600 watts 30 amps 120 volts
2,400 watts 10 amps 240 volts
3,600 watts 15 amps 240 volts
4,800 watts 20 amps 240 volts
7,200 watts 30 amps 240 volts
9,600 watts 40 amps 240 volts
12,000 watts 50 amps 240 volts
14,400 watts 60 amps 240 volts
16,800 watts 70 amps 240 volts
19,200 watts 80 amps 240 volts
21,600 watts 90 amps 240 volts
24,000 watts 100 amps 240 volts

Table: Watts to Amps at 12V DC

Table showing watts converted to amps at 12 volts DC.
Power (Watts) Current (Amps) Voltage (Volts)
5 watts 0.4167 amps 12 volts
10 watts 0.8333 amps 12 volts
15 watts 1.25 amps 12 volts
20 watts 1.667 amps 12 volts
25 watts 2.083 amps 12 volts
30 watts 2.5 amps 12 volts
35 watts 2.917 amps 12 volts
40 watts 3.333 amps 12 volts
45 watts 3.75 amps 12 volts
50 watts 4.167 amps 12 volts
60 watts 5 amps 12 volts
70 watts 5.833 amps 12 volts
80 watts 6.667 amps 12 volts
90 watts 7.5 amps 12 volts
100 watts 8.333 amps 12 volts
120 watts 10 amps 12 volts
180 watts 15 amps 12 volts
240 watts 20 amps 12 volts
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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. Miller, C., Ugly’s Electrical References, 2020 Edition, 2020, Jones & Bartlett Learning, 16-23. https://books.google.com/books?id=1kS8DwAAQBAJ