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Convert electrical power (watts) to current (amps) for DC and AC circuits. Calculate the current draw of your electrical devices.
I(A) = P(W) ÷ V(V)
Current equals power divided by voltage
I(A) = P(W) ÷ (V(V) × PF)
Current equals power ÷ (voltage × power factor)
I(A) = P(W) ÷ (√3 × V(V) × PF)
√3 ≈ 1.732 for three-phase calculations
| Watts (W) | Amps @ 12V | Amps @ 120V | Amps @ 240V |
|---|---|---|---|
| 100 W | 8.33 A | 0.83 A | 0.42 A |
| 200 W | 16.67 A | 1.67 A | 0.83 A |
| 500 W | 41.67 A | 4.17 A | 2.08 A |
| 1,000 W | 83.33 A | 8.33 A | 4.17 A |
| 1,500 W | 125.00 A | 12.50 A | 6.25 A |
| 2,000 W | 166.67 A | 16.67 A | 8.33 A |
| 3,000 W | 250.00 A | 25.00 A | 12.50 A |
| 5,000 W | 416.67 A | 41.67 A | 20.83 A |
| 10,000 W | 833.33 A | 83.33 A | 41.67 A |
Converting watts to amps is the process of determining electrical current (amperes) from a known power consumption (watts) at a given voltage. This relationship is governed by the fundamental power equation P = V × I, where P is power in watts, V is voltage in volts, and I is current in amps. In DC circuits, the conversion is straightforward: divide watts by volts. In AC circuits, the power factor must be included because reactive loads such as motors and transformers draw additional current beyond what is used for real work. Understanding this conversion is essential for electrical safety, proper circuit design, and compliance with the National Electrical Code (NEC). Electricians, engineers, and homeowners routinely use this calculation when sizing circuit breakers, selecting wire gauges, and evaluating whether existing circuits can handle additional loads without overheating or tripping breakers.
Find the wattage of your device on its nameplate, product label, or specifications sheet. For multiple devices on the same circuit, add their wattages together to find the total load.
Standard residential voltages are 120V (North America) or 230V (Europe/Asia). Large appliances may use 240V. Three-phase industrial systems commonly operate at 208V, 480V, or 600V.
For AC circuits, determine the power factor of your load. Resistive loads like heaters have PF = 1.0. Motors typically range from 0.75 to 0.90. If unknown, use 0.8 as a conservative estimate for mixed loads.
For DC: Amps = Watts ÷ Volts. For single-phase AC: Amps = Watts ÷ (Volts × PF). For three-phase AC: Amps = Watts ÷ (√3 × Volts × PF). Always verify the result against your circuit breaker rating and wire size per NEC Table 310.16.
Overloading a circuit causes wires to overheat, potentially causing fires. Calculating amps ensures your circuit breaker and wiring can safely handle the load per NEC Article 210 requirements.
Wire gauge must match the expected current. Using undersized wire increases resistance and heat generation. NEC Table 310.16 specifies ampacity ratings for each wire size and insulation type.
Correctly sized breakers and fuses protect expensive equipment from overcurrent damage. The amp rating determines the right breaker size, typically rated at 125% of the continuous load.
| Amperage | Wire Size (AWG) | Breaker Size | Common Application |
|---|---|---|---|
| 15A | 14 AWG | 15A | Lighting, general outlets |
| 20A | 12 AWG | 20A | Kitchen, bathroom outlets |
| 30A | 10 AWG | 30A | Dryers, water heaters |
| 40A | 8 AWG | 40A | Electric ranges, large AC units |
| 50A | 6 AWG | 50A | EV chargers, sub-panels |
| 60A | 4 AWG | 60A | Large sub-panels, HVAC |
| 100A | 1 AWG | 100A | Main service panel (small homes) |
| 200A | 2/0 AWG | 200A | Main service panel (standard homes) |
At 120V, a 1,500-watt space heater draws 12.5 amps (1500 ÷ 120 = 12.5). Since the NEC requires continuous loads to be limited to 80% of the circuit breaker rating, this heater should be on a dedicated 20-amp circuit (20A × 0.8 = 16A maximum continuous load). Running it on a shared 15-amp circuit with other devices risks tripping the breaker.
Watts measure electrical power — the rate at which energy is consumed or produced. Amps measure electrical current — the flow rate of electrons through a conductor. They are related through voltage by the equation P = V × I. A device can draw many amps at low voltage or few amps at high voltage while consuming the same number of watts. For example, a 60W light bulb draws 0.5A at 120V but would draw 5A at 12V.
Yes, power factor is critical for AC circuits. A power factor less than 1.0 means the device draws more current than the simple watts-divided-by-volts formula suggests. For example, a 1,000-watt motor with a power factor of 0.8 at 120V draws 10.4 amps rather than 8.3 amps. Motors, transformers, fluorescent lighting, and computer power supplies all have power factors below 1.0, typically ranging from 0.6 to 0.95.
For three-phase circuits, use I = P ÷ (√3 × V × PF), where √3 equals approximately 1.732. For example, a 10 kW three-phase motor at 480V with a power factor of 0.85 draws 10,000 ÷ (1.732 × 480 × 0.85) = 14.15 amps per phase. This formula applies to both wye and delta configurations when using line voltage.
Yes, sum the wattage of all devices on the circuit and divide by voltage to find total amps. For a 120V circuit with a 600W microwave, 100W lamp, and 200W TV, the total is 900W ÷ 120V = 7.5A. Per NEC Article 210, continuous loads should not exceed 80% of the breaker rating. On a 15A circuit (12A continuous limit), you have 4.5A of headroom remaining.