How do you convert watts to amps?

Amps = Watts ÷ Volts (for DC and single-phase AC with PF=1). For AC with power factor: Amps = Watts ÷ (Volts × PF). For 3-phase: Amps = Watts ÷ (Volts × √3 × PF). Examples at 120V: 1,200W = 10A, 1,800W = 15A, 2,400W = 20A. At 240V: 3,600W = 15A, 5,760W = 24A.

How do you convert amps to watts?

Watts = Volts × Amps (DC/single-phase PF=1). For AC: Watts = Volts × Amps × Power Factor. For 3-phase: Watts = Volts × Amps × √3 × PF. Examples at 120V: 15A = 1,800W, 20A = 2,400W. At 240V: 30A = 7,200W, 50A = 12,000W. These assume PF=1 (resistive loads like heaters).

What is the difference between watts, VA, and kVA?

Watts (W) = real power (does actual work, generates heat). VA (volt-amps) = apparent power (total power flowing in the circuit). kVA = 1,000 VA. Watts = VA × Power Factor. For purely resistive loads (PF=1), watts = VA. For inductive loads (motors, transformers) with PF<1, VA is higher than watts. Utility billing is based on watts (kWh), but wire and breaker sizing must account for VA (full current flow).

Power Calculator (Watts / Volts / Amps) — Free Electrical Power Conversion Tool 2026 | AllInOneTools

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Power Calculator: The Complete Guide to Watts, Volts, and Amps

Understanding the relationship between watts, volts, and amps is essential for electrical work, appliance selection, circuit sizing, and energy management. This calculator handles the conversions instantly — enter any two values and get the third, along with practical information like breaker sizing and energy costs.

The Power Formulas

Worked Example — Hair Dryer

Hair dryer: 1,800 watts, 120V single-phase
Amps: 1,800 ÷ 120 = 15 amps
Breaker: 20A (15A load on 20A circuit = 75% — good)
Wire: 12 AWG minimum for 20A circuit
Cost to run 30 min/day: 0.9 kWh × $0.13 × 30 days = $3.51/month

Common Watts / Amps Reference

Watts	At 120V	At 240V	Example
600W	5.0A	2.5A	Small heater, blender
1,200W	10.0A	5.0A	Toaster, iron
1,500W	12.5A	6.3A	Space heater, microwave
1,800W	15.0A	7.5A	Hair dryer, griddle
2,400W	20.0A	10.0A	Window AC, circuit max
3,600W	30.0A	15.0A	Small water heater
5,760W	48.0A	24.0A	Clothes dryer
7,200W	—	30.0A	EV charger (Level 2)

Pro Tip — Power Factor Matters

For resistive loads (heaters, incandescent bulbs, toasters), PF = 1.0 — watts = VA. But for inductive loads (motors, LED drivers, computers), PF is less than 1, meaning the circuit draws more amps than the watts alone would suggest. A 1,000W motor with PF=0.8 draws 10.4A at 120V (not 8.3A). Always use power factor when sizing wires and breakers for motors and electronic loads.

Frequently Asked Questions

How do I convert watts to amps?▼

Amps = Watts ÷ Volts (PF=1). With power factor: Amps = Watts ÷ (Volts × PF). At 120V: 1,200W = 10A, 1,800W = 15A, 2,400W = 20A. At 240V: 3,600W = 15A, 7,200W = 30A.

How do I convert amps to watts?▼

Watts = Volts × Amps (PF=1). With PF: Watts = V × A × PF. At 120V: 15A = 1,800W, 20A = 2,400W. At 240V: 30A = 7,200W, 50A = 12,000W.

What is power factor?▼

Ratio of real power (W) to apparent power (VA). PF=1 for resistive loads, PF<1 for motors/electronics. Low PF means higher current for the same real power. Typical: heaters 1.0, motors 0.8-0.9, computers 0.6-0.7.

What's the difference between watts and VA?▼

Watts = real power (does work). VA = apparent power (total current × voltage). Watts = VA × PF. For PF=1 they're equal. For PF<1, VA > Watts. Wire and breaker sizing uses VA (amps); billing uses watts (kWh).

How many watts is a 20-amp circuit?▼

120V: 2,400W max (1,920W continuous per 80% rule). 240V: 4,800W max (3,840W continuous). Common uses: kitchen outlets, garage, bathroom circuits. Wire: 12 AWG minimum.

How do I calculate three-phase power?▼

P = V × I × √3 × PF. √3 ≈ 1.732. Example: 208V, 30A, PF=0.85: P = 208 × 30 × 1.732 × 0.85 = 9,189W. To find amps: I = P ÷ (V × 1.732 × PF).

What size breaker do I need?▼

Calculate amps: A = W ÷ V. Round up to next breaker size (15, 20, 30, 40, 50A). For continuous loads: multiply amps by 1.25. Wire must match: 15A=14AWG, 20A=12AWG, 30A=10AWG, 50A=6AWG.