Electrical Conversion Tool Ohm's Law Current Solver

Watts to Amps Calculator — AC & DC Current Conversion

Calculate electrical current draw in amperes from known wattage and supply voltage across DC, single-phase AC, and three-phase industrial circuits.

Electrical Current Sizing

Watts to Amps Electrical Calculator

Convert electrical power in watts to current in amperes for DC, Single-Phase, and 3-Phase circuits.

I(A) = P(W) / [V · PF] • 3-Phase: I = P / [√3 · V_LL · PF]

Real Electrical Power (Watts) 1,200 W

Circuit Voltage (RMS / DC) 120 V

Circuit Type

Power Factor (cos θ)

Calculated Current Draw

10.00 A

Apparent Power (S): 1,200 VA

NEC Recommended Breaker: 15 Amp Breaker

Minimum Wire (Copper): 14 AWG

Calculation Step:

I = 1,200 W / (120 V · 1.0) = 10.00 Amps

*Breaker sizing based on NEC Article 210.20 continuous load 125% factor (maximum 80% continuous rating).

Interactive Engineering Reference

Ohm's Law & Electrical Power Formula Wheel

Click any quadrant of the formula wheel to solve for Power (P), Voltage (V), Current (I), or Resistance (R) with step-by-step mathematical substitutions.

Interactive Engineering Reference

P = (VRMS)² / R

Click any quadrant of the formula wheel to solve for Power (P), Voltage (V), Current (I), or Resistance (R) with step-by-step mathematical substitutions.

Voltage (VRMS):

Impedance (R Ω):

Result: 99.97 W P = (28.28 V)² / 8 Ω = 99.97 W

Watts to Amps Conversion Formulas (DC, 1-Phase & 3-Phase)

Electrical current in Amperes (I) depends on real wattage, applied voltage, and circuit power factor (PF = cos θ):

Current Calculation Formulas

Direct Current (DC): I (Amps) = Power (Watts) / Voltage (V)

Single-Phase AC: I (Amps) = Power (Watts) / (V_RMS \cdot Power_Factor)

Three-Phase AC (Line-to-Line): I (Amps) = Power (Watts) / (\sqrt3 \cdot V_LL \cdot Power_Factor)

⚠️ HIGH-VOLTAGE ELECTRICAL SAFETY: NEC Continuous Load Rules & Qualified Electricians

1. National Electrical Code (NEC) 80% Continuous Rule: Electrical branch circuit breakers should not be loaded beyond 80% of their maximum rated capacity for continuous loads (loads operating for 3 hours or more). A standard 15 Amp residential circuit is limited to 12.0 Amps continuous (1,440W at 120V); a 20 Amp circuit is limited to 16.0 Amps continuous (1,920W at 120V).

2. High-Voltage Mains & 3-Phase Hazard: Voltages exceeding 50V AC RMS (including 120V, 230V, and 480V 3-Phase systems) present lethal electric shock, electrocution, and arc-flash explosion hazards. Calculations provided here are theoretical planning aids; all physical electrical service installations, branch circuit wiring, and breaker additions must be installed by a licensed, certified electrician in compliance with NFPA 70 / NEC standards.

Watts to Amperes Lookup Matrix Across Common Voltages

Appliance Power (Watts)	Current @ 12V DC	Current @ 24V DC	Current @ 120V AC (PF 1.0)	Current @ 230V AC (PF 1.0)	Breaker Requirement (120V)
100 Watts	8.33 A	4.17 A	0.83 A	0.43 A	15 Amp Circuit
500 Watts	41.67 A	20.83 A	4.17 A	2.17 A	15 Amp Circuit
1,000 Watts (1 kW)	83.33 A	41.67 A	8.33 A	4.35 A	15 Amp Circuit
1,500 Watts	125.00 A	62.50 A	12.50 A	6.52 A	15A / 20A Circuit
1,800 Watts	150.00 A	75.00 A	15.00 A	7.83 A	20 Amp Dedicated
2,400 Watts	200.00 A	100.00 A	20.00 A	10.43 A	20A (240V) / 30A
3,600 Watts	300.00 A	150.00 A	30.00 A	15.65 A	30 Amp Dedicated

Frequently Asked Questions

At 120V AC with a unity power factor (1.0), 1,500 Watts draws exactly 12.5 Amperes (1500 / 120 = 12.5 A), which is within the safe 80% continuous load capacity of a standard 15A household breaker.

The formula for 3-phase electrical current is I = Power (Watts) / (√3 × Line-to-Line Voltage × Power Factor). For example, a 10 kW motor on 400V 3-phase with 0.85 PF draws 10,000 / (1.732 × 400 × 0.85) = 17.0 Amperes.

Under the National Electrical Code (NEC), a circuit breaker should not carry more than 80% of its rated current for continuous loads lasting 3 hours or more. A standard 15A breaker is limited to 12A continuous (1,440W at 120V), and a 20A breaker is limited to 16A continuous (1,920W at 120V).

Because electrical power equals voltage multiplied by current (P = V × I), lowering the voltage by a factor of 10 requires 10 times more current to deliver the same wattage. A 1,200W heater draws 10A at 120V but draws 100A at 12V DC.

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