Watts to Amps Calculator
Single Phase · AC/DC
20.00
Amps
2400W ÷ 120V = 20.00A
Ohm's Law (P = I × V)
I = P ÷ V → 2400 ÷ 120 = 20.00A
Electrical Calculator — Watts to Amps & AWG Wire Gauge Guide
Calculate electrical loads, determine circuit breaker requirements, and reference AWG wire sizes. All values based on NEC 2026 standards.
To calculate Amps from Watts: divide Watts by Volts (I = P / V). For example, a 2400W load on 240V draws 10A. NEC requires a 125% safety factor for continuous loads, meaning a 10A continuous load requires a 15A breaker (the 80% rule).
AWG Wire Gauge & Ampacity Reference
| AWG | mm² | Ampacity 60°C | 75°C | Common Use |
|---|---|---|---|---|
| 14 AWG | 2.08 | 15A | 20A | Lighting, 15A circuits |
| 12 AWG | 3.31 | 20A | 25A | Outlets, 20A circuits |
| 10 AWG | 5.26 | 30A | 35A | Dryers, A/C |
| 8 AWG | 8.37 | 40A | 50A | Ranges, EV Chargers |
| 6 AWG | 13.3 | 55A | 65A | Subpanels |
The Core Principles of Electrical Power Calculations
Whether you are sizing a subpanel, installing a new dedicated circuit, or troubleshooting an overload, accurate power conversion is non-negotiable. Ohm's Law and Watt's Law form the foundation of all electrical work, allowing electricians to calculate missing variables when designing safe power distribution systems.
Ohm's Law vs. Watt's Law
While Ohm's Law (Voltage = Current × Resistance) describes the relationship between electrical pressure and flow, Watt's Law (Power = Voltage × Current) is used specifically to calculate the total work performed or power consumed. For example, if you know an appliance requires 1,500 Watts and runs on a standard 120V household circuit, you divide 1,500 by 120 to determine it will draw 12.5 Amps. This calculation dictates that a 15A breaker and 14 AWG wire are the minimum safe requirements.
Single-Phase vs. Three-Phase Power
In residential settings, power is typically single-phase (120V/240V). The calculations are straightforward. However, in commercial and industrial settings, three-phase power (208V/480V) is standard. Three-phase power delivers energy more efficiently over three alternating currents. When calculating three-phase power, you must multiply the result by the square root of 3 (approximately 1.732). Failing to include this multiplier will result in grossly undersized wires and catastrophic breaker tripping.
Power Factor in Inductive Loads
Resistive loads like incandescent light bulbs and electric heaters have a Power Factor (PF) of 1.0, meaning 100% of the power is converted to useful work. Inductive loads like large HVAC compressors, elevator motors, and transformers have a lower Power Factor (e.g., 0.85) because some energy is required just to sustain the magnetic field. This means the circuit must be sized larger to handle the "apparent power" (Volt-Amps) rather than just the "real power" (Watts).