Watts to Amps Calculator

Q: What is the difference between watts and amps?

Watts measure electric power, which is how much energy a device uses per second. Amps measure electric current, which is how much electricity flows through a wire. You need to know the voltage to convert between the two.

Q: What power factor should I use if I do not know it?

If you do not know the power factor, leave it at 1 . This gives you the minimum amps value. Most home appliances have a power factor between 0.8 and 1.0. Motors and fluorescent lights are usually closer to 0.8.

Q: What is the difference between line-to-line and line-to-neutral voltage?

Line-to-line (L-L) voltage is measured between two hot wires in a three phase system. Line-to-neutral (L-N) voltage is measured between one hot wire and the neutral wire. L-L voltage is higher and uses a √3 factor in the formula. L-N voltage uses a factor of 3 instead.

Q: How many amps does a 1500 watt heater draw on a 120V circuit?

A 1,500-watt heater on a 120-volt circuit draws 12.5 amps . The math is 1500 ÷ 120 = 12.5 A. This is close to the limit of a standard 15-amp circuit breaker, so the heater should ideally be on its own circuit.

Watts To Amps Calculator

Updated May 31, 2026 By Jehan Wadia

Introduction

This Watts to Amps Calculator helps you quickly convert electric power in watts to current in amps. Whether you are working with DC, AC single phase, or AC three phase circuits, this tool does the math for you in seconds. All you need to enter is the power in watts and the voltage in volts. For AC circuits, you can also set the power factor and choose between line-to-line or line-to-neutral voltage.

The basic formula is simple: Amps = Watts ÷ Volts. For AC circuits, the formula also includes the power factor and, for three phase systems, a √3 multiplier. This calculator handles all of these cases so you do not have to worry about picking the right equation. If you need to go the other direction, our Amps to Watts Calculator can help with that conversion.

Electricians, students, engineers, and homeowners can all use this tool to size wires, check circuit breakers, or plan electrical loads. Just pick your current type, enter your values, and hit Calculate to get your result instantly.

How to Use Our Watts to Amps Calculator

Enter your power and voltage values below, and this calculator will instantly convert watts to amps. It works for DC, AC single phase, and AC three phase circuits.

Current Type: Pick the type of current your circuit uses. Choose DC for batteries, AC Single Phase for home outlets, or AC Three Phase for industrial power systems.

Power: Type in the power value of your device. Use the dropdown to select milliwatts (mW), watts (W), or kilowatts (kW). You can find this number on your device's label or manual. If you need to calculate power first, try our Power Calculator.

Voltage: Enter the voltage of your power source. Use the dropdown to pick millivolts (mV), volts (V), or kilovolts (kV). You can also use the preset dropdown to quickly select a common voltage like 120V or 240V.

Power Factor: This field shows up only for AC circuits. Enter a value between 0.01 and 1.0. Most home appliances have a power factor between 0.8 and 1.0. If you are not sure, leave it at 1.

Voltage Type: This field shows up only for AC three phase circuits. Choose Line to Line (L-L) if you measure voltage between two hot wires. Choose Line to Neutral (L-N) if you measure voltage between a hot wire and neutral.

Calculate: Press the Calculate button to see your result in amps and milliamps. The tool also shows the full math so you can check the work. Press Reset to clear all fields and start over.

How to Convert Watts to Amps

Watts and amps are two ways to measure electricity. Watts measure how much power a device uses. Amps measure how much electric current flows through a wire. To find amps from watts, you need to know the voltage, which is the force that pushes electricity through a circuit. For a deeper understanding of the relationship between voltage, current, and resistance, our Ohms Law Calculator is a great companion tool.

Watts to Amps Formula

The basic formula is simple: Amps = Watts ÷ Volts. For example, a 1,000-watt device on a 120-volt circuit draws about 8.33 amps. This formula works directly for DC (direct current), which is the type of power batteries use. You can also explore our Amp Calculator for additional ways to calculate current.

AC Single Phase

For AC single phase power, which is what most homes use, you also need the power factor. The power factor is a number between 0 and 1 that shows how efficiently a device uses electricity. The formula becomes: Amps = Watts ÷ (Volts × Power Factor). Most home appliances have a power factor between 0.8 and 1.0.

AC Three Phase

Factories and large buildings often use AC three phase power. For three phase circuits with line-to-line voltage, the formula is: Amps = Watts ÷ (√3 × Volts × Power Factor). If you measure line-to-neutral voltage instead, you replace √3 with 3. When sizing a generator for three phase loads, our Generator Sizing Calculator can help determine the right capacity.

Why This Matters

Knowing the amps a device draws helps you pick the right wire size, choose the correct circuit breaker, and avoid overloading your electrical system. Overloaded circuits can trip breakers or cause fires. Electricians, engineers, and homeowners all use this conversion to keep electrical systems safe and working properly. For wire sizing projects, check out our Wire Size Calculator, and for checking voltage loss over long cable runs, use our Voltage Drop Calculator. If you want to estimate how much your electrical usage costs, our Electricity Cost Calculator can help you plan your energy budget. You may also find our Voltage Divider Calculator, Parallel Resistor Calculator, and Capacitor Calculator useful for related circuit design work.

Frequently asked questions

What is the difference between watts and amps?

Watts measure electric power, which is how much energy a device uses per second. Amps measure electric current, which is how much electricity flows through a wire. You need to know the voltage to convert between the two.

Can I use this calculator for both 120V and 240V circuits?

Yes. You can type any voltage into the voltage field or use the preset dropdown to quickly select common voltages like 120V, 240V, 480V, and others. The calculator works with any voltage value.

What power factor should I use if I do not know it?

If you do not know the power factor, leave it at 1. This gives you the minimum amps value. Most home appliances have a power factor between 0.8 and 1.0. Motors and fluorescent lights are usually closer to 0.8.

What is the difference between line-to-line and line-to-neutral voltage?

Line-to-line (L-L) voltage is measured between two hot wires in a three phase system. Line-to-neutral (L-N) voltage is measured between one hot wire and the neutral wire. L-L voltage is higher and uses a √3 factor in the formula. L-N voltage uses a factor of 3 instead.

Why does the power factor only appear for AC circuits?

DC circuits deliver power directly, so watts divided by volts gives you the exact amps. In AC circuits, the voltage and current waves can be out of sync. The power factor measures how far out of sync they are. This affects how many amps are needed to deliver the same amount of real power.

How do I find the wattage of my device?

Check the label on the back or bottom of your device. It usually lists the wattage in watts (W). You can also find it in the product manual or on the manufacturer's website. Some labels show kilowatts (kW) instead, which equals 1,000 watts.

Can I enter milliwatts or kilowatts instead of watts?

Yes. Use the dropdown next to the power field to select mW (milliwatts), W (watts), or kW (kilowatts). The calculator converts your input to watts automatically before doing the math.

How many amps does a 1500 watt heater draw on a 120V circuit?

A 1,500-watt heater on a 120-volt circuit draws 12.5 amps. The math is 1500 ÷ 120 = 12.5 A. This is close to the limit of a standard 15-amp circuit breaker, so the heater should ideally be on its own circuit.

What happens if I enter zero for voltage?

The calculator will show an error message. Voltage must be greater than zero because you cannot divide by zero. Every real circuit needs some voltage to push current through it.

Is the result in amps the same as the breaker size I need?

Not exactly. The amps result shows how much current your device draws. Circuit breakers should be rated higher than the load. A common rule is that continuous loads should not exceed 80% of the breaker rating. For example, a 16-amp load needs at least a 20-amp breaker.

Why does three phase use less amps than single phase for the same wattage?

Three phase power splits the load across three wires instead of one. This means each wire carries less current. The √3 factor in the formula accounts for this. It makes three phase systems more efficient for high-power equipment.

Can I use this calculator for solar panels or inverters?

Yes. Solar panels produce DC power, so select the DC mode. For inverters that output AC power, select AC Single Phase or AC Three Phase depending on your setup. Enter the wattage and voltage from the panel or inverter specifications.

What does the milliamps result mean?

Milliamps (mA) is a smaller unit of current. One amp equals 1,000 milliamps. The milliamps result is useful for small electronics and low-power devices where the current is less than one amp.

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