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Amps to Watts Calculator

Convert electrical current (amps) to power (watts) for DC and AC circuits. Supports single-phase and three-phase AC systems.

Calculate Watts from Amps

Circuit Type

Current (Amps)

Voltage (Volts)

Results:

Watts (W)1,200

Kilowatts (kW)1.2

Milliwatts (mW)1,200,000

Formulas

DC Circuit

P(W) = I(A) × V(V)

Power equals current times voltage

AC Single Phase

P(W) = I(A) × V(V) × PF

Power equals current × voltage × power factor

AC Three Phase

P(W) = √3 × I(A) × V(V) × PF

√3 ≈ 1.732 for three-phase calculations

Quick Examples

•15A at 120V = 1,800W (typical US circuit)
•20A at 240V = 4,800W (electric dryer)
•10A at 12V = 120W (car accessory)

What Is Amps to Watts Conversion?

Converting amperes to watts determines the actual power consumption of electrical devices and circuits. Watts measure the rate of energy consumption: for DC, W = A × V. For single-phase AC, W = A × V × PF. For three-phase AC, W = A × V × PF × √3. This conversion is essential for electrical load calculations, energy consumption estimation, circuit design, and compliance with the National Electrical Code. Every electrical device from LED bulbs to industrial motors has both amperage and wattage specifications — understanding how they relate enables proper circuit design and energy management.

How to Calculate Amps to Watts Conversion

1
Identify Circuit Type
Determine DC, single-phase AC, or three-phase AC. Check the power source: batteries and solar panels are DC; wall outlets are single-phase AC; industrial feeds are typically three-phase AC.
2
Measure or Find Amperage
Use a clamp meter for existing circuits or find rated amps on device nameplates and specification sheets. For multiple devices on one circuit, sum individual amperages.
3
Enter Voltage
Standard voltages: 12V/24V/48V (DC), 120V/240V (residential AC), 208V/480V (commercial three-phase). Measure with a multimeter for accuracy.
4
Enter Power Factor for AC
Power factor ranges from 0 to 1. Common values: 1.0 (resistive heaters), 0.95 (modern LED drivers), 0.85 (motors), 0.60 (old fluorescent ballasts).
5
Review Wattage
The result shows real power in watts. Use this for energy calculations (Wh = W × hours), circuit loading assessments, and wire sizing verification.

Why Amps to Watts Conversion Matters

Energy Bill Estimation

Electricity is metered in kilowatt-hours (kWh). Converting device amps to watts and multiplying by hours gives energy consumption. At $0.12/kWh, a 1500W heater running 8 hours costs $1.44/day.

Circuit Capacity Verification

Standard 15A/120V circuits provide 1800W, and 20A circuits provide 2400W. Converting each load from amps to watts ensures total circuit loading stays within safe limits.

Wire Sizing Verification

NEC wire sizing depends on amperage, but load calculations often start in watts. Converting between amps and watts ensures conductors are properly sized for the actual power being delivered.

Renewable Energy System Design

Solar panel output in watts, battery capacity in Ah, and inverter ratings in VA all require amps-to-watts conversions for proper system sizing and energy balance calculations.

Electrical Safety Tips & Best Practices

Resistive Loads Simplify the Math

For purely resistive loads (heaters, incandescent bulbs, toasters), power factor is 1.0, so Watts = Amps × Volts directly. No power factor correction needed.

NEC 80% Rule for Continuous Loads

For loads operating 3+ hours continuously, NEC requires circuit capacity at 125% of load (or equivalently, load at 80% of circuit rating). A 20A circuit supports only 16A (1920W at 120V) continuously.

Phantom Loads Add Up

Standby power (phantom loads) from electronics typically draws 1-10W each. Multiple devices can add 50-100W to your baseline, costing $50-$100/year.

Use Kill-A-Watt Meters

Plug-in power meters directly measure watts, amps, volts, and power factor simultaneously. They are the most accurate way to determine actual power consumption of plug-in devices.

Amps to Watts Conversion Table (DC)

Amps (A)	Watts @ 12V	Watts @ 120V	Watts @ 240V
1 A	12 W	120 W	240 W
2 A	24 W	240 W	480 W
5 A	60 W	600 W	1,200 W
10 A	120 W	1,200 W	2,400 W
15 A	180 W	1,800 W	3,600 W
20 A	240 W	2,400 W	4,800 W
30 A	360 W	3,600 W	7,200 W
40 A	480 W	4,800 W	9,600 W
50 A	600 W	6,000 W	12,000 W
100 A	1,200 W	12,000 W	24,000 W

Frequently Asked Questions

How do I convert amps to watts?

For DC circuits, multiply amps by volts (P = I × V). For AC circuits, you also need to factor in the power factor. A 15-amp circuit at 120 volts provides 1,800 watts.

What is power factor?

Power factor is a measure of how efficiently electrical power is being used. It ranges from 0 to 1, with 1 being perfect efficiency. Resistive loads like heaters have a power factor of 1, while motors typically have 0.8-0.85.

Why is three-phase calculation different?

Three-phase power delivers power more efficiently using three alternating currents offset by 120 degrees. The √3 (approximately 1.732) factor accounts for this phase relationship.

How many watts is 15 amps at 120V?

For a resistive load: 15A × 120V = 1800W. With a typical power factor of 0.85: 15A × 120V × 0.85 = 1530W. A standard 15-amp circuit breaker protects circuits up to 1800 VA, but continuous loads should not exceed 1440W (80% rule).

How many amps does a 1500W heater draw?

At 120V: 1500W ÷ 120V = 12.5 amps. At 240V: 1500W ÷ 240V = 6.25 amps. Resistive heaters have a power factor of 1.0, so the calculation is straightforward. A 1500W heater needs at least a 15A circuit at 120V.

Why is power factor important in amps to watts conversion?

Power factor accounts for the phase difference between voltage and current in AC circuits. Without it, you calculate apparent power (VA), not real power (W). A motor drawing 10A at 120V with PF=0.80 consumes only 960W, not 1200W. The remaining 240 VA is reactive power.

What uses the most watts in a home?

Top household power consumers: central AC (3000-5000W), electric water heater (4500W), electric dryer (5400W), electric oven/range (2000-5000W), space heaters (1500W), hair dryers (1000-1875W). HVAC and water heating typically account for 50-60% of residential electricity use.

How do I calculate three-phase watts?

Three-phase watts = Amps × Volts × √3 × Power Factor. For example: 30A at 480V with PF=0.85: W = 30 × 480 × 1.732 × 0.85 = 21,198W (21.2 kW). The √3 factor accounts for the 120° phase offset between the three phases.

Related Electrical Calculators

⚡Watts to Amps ⚡Volts to Watts ⚡Ohm's Law ⚡Amps to Kilowatts

References & Industry Standards

NEC Article 210 - Branch Circuits
NEC Article 220 - Branch-Circuit, Feeder, and Service Load Calculations
IEEE 1459 - Standard Definitions for the Measurement of Electric Power
ENERGY STAR - Understanding Electricity Measurements

Last updated: 2026-02-01 | Reviewed by UnitTables Engineering Team

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What Is Amps to Watts Conversion?

How to Calculate Amps to Watts Conversion

Identify Circuit Type

Determine DC, single-phase AC, or three-phase AC. Check the power source: batteries and solar panels are DC; wall outlets are single-phase AC; industrial feeds are typically three-phase AC.

Measure or Find Amperage

Use a clamp meter for existing circuits or find rated amps on device nameplates and specification sheets. For multiple devices on one circuit, sum individual amperages.

Enter Voltage

Standard voltages: 12V/24V/48V (DC), 120V/240V (residential AC), 208V/480V (commercial three-phase). Measure with a multimeter for accuracy.

Enter Power Factor for AC

Power factor ranges from 0 to 1. Common values: 1.0 (resistive heaters), 0.95 (modern LED drivers), 0.85 (motors), 0.60 (old fluorescent ballasts).

Review Wattage

The result shows real power in watts. Use this for energy calculations (Wh = W × hours), circuit loading assessments, and wire sizing verification.

Why Amps to Watts Conversion Matters

Energy Bill Estimation

Electricity is metered in kilowatt-hours (kWh). Converting device amps to watts and multiplying by hours gives energy consumption. At $0.12/kWh, a 1500W heater running 8 hours costs $1.44/day.

Circuit Capacity Verification

Standard 15A/120V circuits provide 1800W, and 20A circuits provide 2400W. Converting each load from amps to watts ensures total circuit loading stays within safe limits.

Wire Sizing Verification

NEC wire sizing depends on amperage, but load calculations often start in watts. Converting between amps and watts ensures conductors are properly sized for the actual power being delivered.

Renewable Energy System Design

Solar panel output in watts, battery capacity in Ah, and inverter ratings in VA all require amps-to-watts conversions for proper system sizing and energy balance calculations.

Electrical Safety Tips & Best Practices

Resistive Loads Simplify the Math

For purely resistive loads (heaters, incandescent bulbs, toasters), power factor is 1.0, so Watts = Amps × Volts directly. No power factor correction needed.

NEC 80% Rule for Continuous Loads

Phantom Loads Add Up

Standby power (phantom loads) from electronics typically draws 1-10W each. Multiple devices can add 50-100W to your baseline, costing $50-$100/year.

Use Kill-A-Watt Meters

Plug-in power meters directly measure watts, amps, volts, and power factor simultaneously. They are the most accurate way to determine actual power consumption of plug-in devices.

Amps (A)

Watts @ 12V

Watts @ 120V

Watts @ 240V

1 A

12 W

120 W

240 W

2 A

24 W

240 W

480 W

5 A

60 W

600 W

1,200 W

10 A

120 W

1,200 W

2,400 W

15 A

180 W

1,800 W

3,600 W

20 A

240 W

2,400 W

4,800 W

30 A

360 W

3,600 W

7,200 W

40 A

480 W

4,800 W

9,600 W

50 A

600 W

6,000 W

12,000 W

100 A

1,200 W

12,000 W

24,000 W

Frequently Asked Questions

How do I convert amps to watts?

For DC circuits, multiply amps by volts (P = I × V). For AC circuits, you also need to factor in the power factor. A 15-amp circuit at 120 volts provides 1,800 watts.

What is power factor?

Why is three-phase calculation different?

Three-phase power delivers power more efficiently using three alternating currents offset by 120 degrees. The √3 (approximately 1.732) factor accounts for this phase relationship.