Watts, Amps and Volts Calculator

Convert watts to amps, amps to watts, or find the voltage, for DC, single-phase AC and three-phase AC circuits — with power factor and kW input.

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How many amps is 1,500 watts?

Amps = watts ÷ volts (× power factor on AC). At 120 V with a resistive load, 1,500 W is 12.5 A; at 230 V it is about 6.52 A. For three-phase, divide by √3 × line-to-line volts × power factor.

Cost: Free, no limits
Upload: None — runs on your device
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Works offline: Yes, once loaded

How to convert watts to amps

Choose the circuit type
DC, AC single-phase or AC three-phase. Three-phase asks for the line-to-line voltage.
Choose what to solve for
Amps, watts or volts. The calculator asks for the other two.
Enter the known values
Power can be entered in W or kW. On AC, set the power factor — leave it at 1 for resistive loads.
Read every figure
The answer is shown with watts, kilowatts, amps, volts and, on AC, apparent power in VA and kVA.

Examples

1,500 W, 120 V, single-phase, PF 112.5 A
A typical space heater on a North American socket.
10 kW, 400 V line-to-line, three-phase, PF 0.85≈ 16.98 A
10,000 ÷ (1.732 × 400 × 0.85).
12 V DC, 5 A60 W (0.06 kW)
On DC there is no power factor.

Key features of the Watts, Amps and Volts Calculator

Solves for watts, amps or volts from the other two
DC, single-phase AC and three-phase AC with the √3 factor
Power factor input for AC, starting at 1 for resistive loads
Power entered in watts or kilowatts; results shown in both
Apparent power in VA and kVA for AC circuits

What it calculates

Circuits

DC
AC single-phase
AC three-phase (line-to-line voltage)

Solve for

Amps
Watts
Volts

Units shown

W
kW
A
V
VA and kVA (AC)

When should you use this?

Checking how many amps an appliance draws from its wattage label.
Working out kW to amps for a three-phase motor or heater from its rating plate.
Converting watts to kilowatts, or estimating the wattage a 12 V or 24 V DC system can supply at a given current.

Limitations

It does not size wiring, fuses or breakers. That depends on cable length, installation method, temperature and local electrical code — ask an electrician.
The power factor is an input, not something the calculator can know. A wrong PF gives a wrong current for motors and electronics.
Three-phase results assume a balanced load across the phases.
Starting (inrush) current of motors and transformers can be several times the running current and is not shown.

Troubleshooting

The current looks far too high or low

Check the power unit (W or kW) and, for three-phase, that the voltage is line-to-line.

It says the power factor must be more than 0 and no more than 1

Power factor is a ratio. Enter it as a decimal, such as 0.85, not as 85.

Common mistakes to avoid

Using the line-to-neutral voltage (230 V, 120 V) in the three-phase formula instead of the line-to-line voltage (400 V, 208 V).
Leaving the power factor at 1 for a motor, which understates the current it draws.
Entering kilowatts while the unit is set to W — the result is a thousand times too small.

Pro tips

Tips for better results

Motors
Take the power factor from the rating plate
For anything with a motor, take the power factor from the rating plate. If it only gives volts and amps, VA is what you can calculate, not watts.
Supply voltage
Real mains voltage moves the current a little
Mains voltage varies: 120 V and 230 V are nominal figures, and the real supply can be a few percent either way, which moves the current in proportion.
Circuits
Add up every load on the circuit first
Add up the watts of everything on one circuit before converting to amps — the breaker sees the total, not each appliance.

The three formulas

For direct current, power is simply voltage times current: P = V × I. A 12 V lamp drawing 5 A uses 60 W.

For single-phase AC — ordinary household sockets — the same product is multiplied by the power factor: P = V × I × PF. The power factor is the share of the current that does useful work. For a purely resistive load such as a kettle, an electric heater or an incandescent bulb, voltage and current rise and fall together and the power factor is 1, which is why the calculator starts there. Motors, compressors and many power supplies draw current that is out of step with the voltage, so their power factor is lower — often somewhere between 0.6 and 0.95 — and they draw more amps for the same watts.

For three-phase AC the formula gains a factor of √3 (about 1.732): P = √3 × V × I × PF, where V is the line-to-line voltage — the voltage measured between two phases, such as 400 V in Europe or 208 V and 480 V in North America. Using the line-to-neutral voltage here instead gives a current √3 times too high.

Watts, volt-amperes and kilowatts

Watts measure real power, the energy actually used. Volt-amperes (VA) are simply volts times amps (times √3 on three-phase) and measure apparent power — what the wiring and supply have to carry. The two are equal when the power factor is 1. Generators and UPS units are often rated in VA or kVA for that reason. Watts to kilowatts is a plain division by 1,000: 1,500 W is 1.5 kW. The calculator shows every figure in both.

What it does not do

Knowing the current a load draws is the start of choosing a cable or breaker, not the end. Cable size also depends on its length, how it is installed and bundled, the ambient temperature and the allowed voltage drop, and breakers are chosen with safety margins your local electrical code sets. Use this to understand the numbers, and ask a qualified electrician to design anything you will connect to the mains.

Privacy

The Watts, Amps and Volts Calculator runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

What next?

For power ratings given in other units.

Convert kW, horsepower and BTU/h

Watts, Amps and Volts Calculator — questions

How do you convert watts to amps?

Divide watts by volts for DC. For single-phase AC divide by volts × power factor, and for three-phase divide by √3 × line-to-line volts × power factor. A 1,500 W heater on 120 V draws 12.5 A.

How do I convert kW to amps?

Multiply kW by 1,000 to get watts, then use the formula for your circuit — or choose kW as the power unit and the calculator does it. 10 kW on a 480 V three-phase supply at power factor 1 is about 12.03 A.

What power factor should I use?

1 for resistive loads such as heaters, kettles, toasters and incandescent lamps. For motors and electronics use the figure on the rating plate or datasheet; if none is given, the result at 1 is the lowest current the load could draw.

Why is there a √3 in the three-phase formula?

Because the three phases are 120° apart, the voltage between two phases is √3 times the voltage from each phase to neutral. The formula uses that line-to-line voltage, so the √3 brings the total back to the power actually delivered.

Can I use this to choose a breaker or cable?

No. It converts between power, current and voltage only. Cable and breaker sizing depend on installation conditions and local electrical code, so consult a qualified electrician.

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