Amps to Watts Calculator
Convert current to power for DC, AC single-phase, and AC three-phase circuits
What is an Amps to Watts Calculator?
The Amps to Watts Calculator is a free online electrical tool that converts current (A) to power (W) when you know the voltage (V) or resistance (Ω). Amps measure how many electrons flow through a conductor per second. Watts measure the rate of energy transfer — how much work the electricity performs. Converting amps to watts is essential when calculating power consumption, sizing generators, and determining electrical loads for circuits. Most appliance labels show amps, but you need watts to calculate energy costs and total circuit load.
Why Convert Amps to Watts?
Many electrical devices list their current draw in amps on their nameplates, but power bills and energy calculations use watts (or kilowatts). Converting amps to watts lets you calculate energy costs (kWh = W × hours ÷ 1000), determine total circuit load to prevent overloads, size generators and inverters for backup power, and compare the energy consumption of different appliances. This calculator handles all circuit types and shows the formula used in every calculation.
Amps to Watts Formula
The complete set of formulas for converting current to power
DC Amps to Watts Calculation
Direct current circuits use the simplest amps to watts formula
DC amps to watts conversion uses the formula P(W) = V(V) × I(A). Multiply voltage by current to get power in watts. This applies to batteries, solar panels, USB devices, and all DC circuits. No power factor is needed for DC.
A 12 V car battery delivering 50 A to a starter motor: P = 12 × 50 = 600 W. A USB port at 5 V delivering 2.4 A: P = 5 × 2.4 = 12 W.
Single Phase
AC conversions include power factor for accurate real power calculation
AC single-phase amps to watts conversion uses P(W) = V(V) × I(A) × PF. The power factor (PF) accounts for the difference between apparent power and real power. Without PF, you get apparent power in volt-amps (VA), not real power in watts (W).
A vacuum cleaner drawing 12 A from a 120 V outlet with PF = 0.85: P = 120 × 12 × 0.85 = 1224 W.
Three Phase & Resistance Method
Line-to-Line Voltage
Use line-to-line voltage for three-phase motor loads and industrial equipment.
A three-phase motor drawing 20 A at 480 V with PF = 0.9: P = 1.732 × 480 × 20 × 0.9 = 14,966 W ≈ 15 kW.
Line-to-Neutral Voltage
Use line-to-neutral voltage for single-phase loads on a three-phase panel.
A lighting load drawing 5 A at 277 V line-to-neutral with PF = 1.0: P = 3 × 277 × 5 × 1.0 = 4155 W.
Amps to Watts using Resistance
Convert amps to watts using resistance with the formula P(W) = I²(A) × R(Ω). This formula derives from combining Watt's Law (P = V × I) and Ohm's Law (V = I × R). Square the current and multiply by resistance to get power.
A 10 A current through a 12 Ω resistor: P = 10² × 12 = 100 × 12 = 1200 W.
Example Calculations
Step-by-step amps to watts conversion examples
Household Circuit Check
Given: Current (I) = 15 A, Voltage (V) = 120 V
AC Motor Power Consumption
Given: Current (I) = 8 A, Voltage (V) = 240 V, PF = 0.85
Using Resistance Only
Given: Current (I) = 5 A, Resistance (R) = 24 Ω
Amps to Watts Conversion Chart
Quick reference for common amperages at 120V and 240V
| Current (A) | At 120V (W) | At 240V (W) |
|---|---|---|
| 1 A | 120 W | 240 W |
| 2 A | 240 W | 480 W |
| 5 A | 600 W | 1,200 W |
| 10 A | 1,200 W | 2,400 W |
| 12 A | 1,440 W | 2,880 W |
| 15 A | 1,800 W | 3,600 W |
| 20 A | 2,400 W | 4,800 W |
| 30 A | 3,600 W | 7,200 W |
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Convert power (W) to current (A) for DC and AC circuits with power factor support.
Amps to Watts Calculator
Convert current (A) to power (W) for DC, AC single-phase, and AC three-phase circuits.
Volts to Amps Calculator
Convert voltage (V) to current (A) using Ohm's Law or Watt's Law.
Amps to Volts Calculator
Convert current (A) to voltage (V) using Ohm's Law or Watt's Law.
Frequently Asked Questions
How many watts is 15 amps?
15 amps equals different wattages depending on voltage. At 120 V: P = 120 × 15 = 1800 W. At 240 V: P = 240 × 15 = 3600 W. At 12 V (DC): P = 12 × 15 = 180 W. A standard 15 A residential circuit breaker at 120 V can deliver up to 1800 W (or 1440 W continuous using the 80% rule).
How to calculate watts from amps?
Multiply amps by volts to get watts: P(W) = V(V) × I(A). For AC circuits, also multiply by the power factor: P = V × I × PF. For example, 10 A at 120 V = 1200 W. If voltage is unknown, use P = I² × R (amps squared times resistance in ohms).
How many watts is 20 amps at 120 volts?
20 amps at 120 volts equals 2400 watts: P = 120 × 20 = 2400 W. This is the maximum capacity of a 20 A circuit breaker. Using the 80% rule, the recommended continuous load is 20 × 0.8 = 16 A = 1920 W.
What is the amps to watts formula?
The amps to watts formula is P(W) = V(V) × I(A) for DC. For AC single-phase: P = V × I × PF. For three-phase line-to-line: P = √3 × V × I × PF. Using resistance when voltage is unknown: P = I² × R.
How many watts can a 30 amp breaker handle?
A 30 amp breaker can handle: At 120 V: 30 × 120 = 3600 W maximum. At 240 V: 30 × 240 = 7200 W maximum. Using the 80% rule for continuous loads: At 120 V = 2880 W, at 240 V = 5760 W. Most 30 A circuits are 240 V and used for dryers, water heaters, and small AC units.
How do you convert amps to watts without voltage?
Use the resistance formula: P = I² × R. Measure resistance with a multimeter, square the current in amps, and multiply by resistance in ohms. For example, 5 A through 20 Ω: P = 25 × 20 = 500 W. Without either voltage or resistance, amps alone cannot be converted to watts.
What is the difference between amps and watts?
Amps measure electrical current — the rate of electron flow through a conductor. Watts measure electrical power — the rate of energy transfer. Think of a water hose: amps are the flow rate (liters per minute), volts are the water pressure, and watts are the total amount of work the water can do. Watts = Volts × Amps.
How many watts is 10 amps at 240 volts?
10 amps at 240 volts equals 2400 watts: P = 240 × 10 = 2400 W = 2.4 kW. This is a common load for electric ovens, water heaters, and central air conditioning units on 240 V circuits.