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Amps to Watts Calculator

Convert current in amps to power in watts for DC, single-phase AC, and three-phase AC circuits. Features unit dropdowns (mA–kA, mV–kV), power factor presets, kW auto-display, and electricity cost estimation.

Power
1,200 W
1.20 kW

How to Convert Amps to Watts

Converting amps to watts calculates the actual power consumption of a device based on its current draw and the circuit voltage. This is the most comprehensive amps-to-watts calculator online—featuring unit dropdowns, power factor presets for accurate AC calculations, and automatic kWh cost estimation.

1

Select Circuit

Choose DC for batteries/solar, or AC for household and industrial. Three-phase is standard for commercial/industrial loads.

2

Enter with Units

Input current (mA/A/kA) and voltage (mV/V/kV). For AC, use power factor presets or enter a custom value.

3

Get Power + Cost

Result shows watts, kilowatts (for large values), and estimated hourly electricity cost at $0.16/kWh.

Amps to Watts Formula

DC
P = I × V
P = Power (watts), I = Current (amps), V = Voltage (volts)
Single-Phase AC
P = I × V × PF
PF = Power factor (0–1)
Three-Phase AC
P = √3 × I × V × PF
√3 = 1.732, V = Line-to-line voltage

Example Calculations

DC: 10A at 12V (Car Audio)
P = 10 × 12 = 120W
Result: 120W
Typical car subwoofer amplifier. Uses about 10A from a 12V battery.
DC: 15A at 120V (Max Circuit)
P = 15 × 120 = 1,800W
Result: 1,800W
Maximum for a 15A/120V circuit. NEC says max 1,440W continuous (80% rule).
1-Phase AC: 20A, 240V, PF=0.9
P = 20 × 240 × 0.9 = 4,320W
Result: 4,320W (4.32 kW)
A large AC unit. Apparent power = 4,800 VA, but only 4,320W does useful cooling work.
3-Phase: 30A, 480V, PF=0.85
P = 1.732 × 30 × 480 × 0.85 = 21,198W
Result: 21,198W (21.2 kW)
A 30HP industrial motor. At $0.16/kWh, this costs $3.39/hour to run.
USB-C: 3A at 5V
P = 3 × 5 = 15W
Result: 15W
Standard USB-C 3.0 charging. USB PD can go up to 5A at 20V = 100W for laptops.

Amps to Watts Conversion Table (DC / PF=1)

Amps5V12V24V120V240V480V
1A5W12W24W120W240W480W
2A10W24W48W240W480W960W
5A25W60W120W600W1,200W2,400W
10A50W120W240W1,200W2,400W4,800W
15A75W180W360W1,800W3,600W7,200W
20A100W240W480W2,400W4,800W9,600W
30A150W360W720W3,600W7,200W14,400W
50A250W600W1,200W6,000W12,000W24,000W

Common Appliance Power Consumption

ApplianceAmpsVoltageWattsCost/Hour*
LED Bulb0.1A120V12W$0.002
Laptop Charger0.5A120V60W$0.010
Desktop PC2.5A120V300W$0.048
Microwave10A120V1,200W$0.192
Space Heater12.5A120V1,500W$0.240
Central AC16A240V3,840W$0.614
Clothes Dryer24A240V5,760W$0.922
Electric Range40A240V9,600W$1.536
EV Charger L240A240V9,600W$1.536
Hot Tub50A240V12,000W$1.920

*At $0.16/kWh US average rate

⚠️ Safety: Circuit Loading & NEC Guidelines

  • NEC 80% continuous rule: 15A circuit → 12A / 1,440W continuous. 20A → 16A / 1,920W. 30A → 24A / 5,760W at 240V.
  • Shared circuits: All devices on a circuit share the total capacity. Two 1,000W appliances on a 15A/120V circuit (1,800W max) will trip the breaker. Don't overload shared circuits.
  • Three-phase caution: Three-phase circuits require professional installation. Phase imbalance (uneven loading across phases) can damage motors and trip breakers. Always balance loads evenly.
  • Electricity cost: At $0.16/kWh, a 1,500W heater costs $0.24/hour, $1.92/8 hours, or $57.60/month (8 hrs/day). Use the cost estimate in our calculator for planning.

Understanding Amps to Watts Conversion

Knowing how to convert amps to watts is essential for electricity cost management and safety. The current rating of a device (amps) tells you how much charge flows per second, but the power (watts) tells you how much energy is actually consumed—which is what appears on your electricity bill. Understanding this relationship helps you make informed decisions about appliance usage, circuit planning, and energy efficiency.

In residential applications, most circuits are either 15A or 20A at 120V, providing 1,800W or 2,400W respectively. Heavy appliances like dryers (30A at 240V = 7,200W) and ranges (50A at 240V = 12,000W) use dedicated 240V circuits. Industrial facilities use three-phase 480V power for the most efficient delivery of large loads—a 100A three-phase circuit at 480V delivers over 83kW, enough to run a small factory floor.

For the reverse calculation, use our Watts to Amps Calculator. When working with AC circuits, our AC Wattage Calculator goes further — it calculates real power, apparent power (VA), and reactive power (VAR) with a full power triangle visualization, including single-phase and three-phase modes. To determine apparent power for UPS and generator sizing, use our Amps to VA Calculator. To find voltage from amps, try our Amps to Volts Calculator.

Frequently Asked Questions

For DC: multiply amps by volts (P = I × V). For single-phase AC: multiply amps × volts × power factor (P = I × V × PF). For three-phase AC: multiply √3 × amps × volts × power factor (P = 1.732 × I × V × PF). The power factor accounts for the phase difference between voltage and current in AC circuits.
DC: P = I × V. Single-phase AC: P = I × V × PF. Three-phase AC: P = √3 × I × V × PF. P is power in watts, I is current in amps, V is voltage in volts, and PF is power factor (0 to 1). PF = 1.0 for resistive loads, 0.8 for motors, 0.9 for electronics, 0.6 for fluorescent lighting.
For DC or resistive AC (PF=1): 15A × 120V = 1,800W. This is the maximum total wattage for a 15A circuit. The NEC 80% rule means continuous loads should not exceed 80% of this: 1,440W continuous. A 20A circuit allows 2,400W total (1,920W continuous).
20A × 240V = 4,800W for DC or PF=1. This is common for 240V circuits serving electric water heaters, large AC units, and some EV chargers. With a motor power factor of 0.85: 20 × 240 × 0.85 = 4,080W of real power (the motor draws 4,800VA apparent power but only uses 4,080W productively).
Amps measure the rate of electrical current flow (how many electrons pass a point per second—1 amp = 6.24 × 10¹⁸ electrons/second). Watts measure power (the rate of energy transfer—1 watt = 1 joule/second). Think of a river: amps is how much water flows (gallons/second), watts is how much work the water does (turning a waterwheel).
No. Power factor only applies to AC circuits. In DC, voltage and current are constant and always "in phase," so P = V × I exactly. AC circuits may have inductors (motors) or capacitors (power supplies) that cause current to lead or lag voltage, reducing the fraction of apparent power that does useful work.
Resistive loads (heaters, incandescent bulbs, toasters): PF ≈ 1.0. Induction motors (refrigerators, AC units, washing machines): PF = 0.6–0.85. LED drivers and switched-mode power supplies: PF = 0.5–0.95 (varies widely). Modern appliances increasingly include active PFC (power factor correction) circuits that improve PF to 0.95+.
P = √3 × I × V_LL × PF, where V_LL is line-to-line voltage. The √3 (1.732) factor accounts for the 120° phase offset. For line-to-neutral: P = 3 × I × V_LN × PF. Common three-phase voltages: 208V (commercial US), 480V (industrial US), 400V (Europe), 600V (Canada industrial).
Converting amps to watts tells you actual power consumption, which is essential for: (1) calculating electricity costs (billed in kWh = watts × hours / 1000), (2) sizing generators and UPS systems, (3) designing solar installations, (4) comparing energy efficiency of devices, (5) calculating heat generation (all electrical power becomes heat eventually).
US 120V standard outlet: 15A or 20A circuit (1,800W or 2,400W). US 240V dryer outlet (NEMA 14-30): 30A (7,200W). US 240V range outlet (NEMA 14-50): 50A (12,000W). European 230V standard outlet: 16A (3,680W). UK 230V standard outlet: 13A (2,990W). Australian 230V standard outlet: 10A (2,300W).

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