Watts to amps calculator
Power, voltage, system and power factor: you get current, apparent power and an indicative breaker size.
Current
10 A
- Current10 A
- Apparent power2300 VA
- Indicative minimum breaker10 A
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How it's calculated (visible formula)
single-phase: I = P ÷ (V × PF); three-phase: I = P ÷ (√3 × V × PF)
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Find the appliance wattage (nameplate).
- Enter supply voltage (120/240 V single-phase or 208/480 V three-phase).
- Choose single-phase or three-phase.
- Enter power factor (1 for heaters).
- Get the current and compare with the circuit.
Worked example: 1,500 W heater on 120 V
- Single-phase, PF = 1
- I = 1,500 ÷ (120 × 1) = 12.5 A
→ 12.5 A — use a 20 A circuit (80% continuous rule).
Common mistakes
- Forgetting power factor on motors.
- Using the wrong voltage (120 vs 240).
- Sizing wire by current alone, ignoring run length.
Pro tips
- Add up everything on the same circuit.
- Motors draw 3–7× running current at start-up.
- Keep continuous loads at 80% of the breaker rating.
- Check service capacity before adding big loads.
From calculation to quote
Add labor, overhead and your margin, and generate the professional PDF.
FAQs
- How many amps is 1,500 watts?
- 12.5 A at 120 V; 6.25 A at 240 V.
- Three-phase?
- I = P ÷ (1.732 × V × PF).
- What power factor?
- 1 for heaters; 0.8–0.9 for motors.
- How many amps is 2,000 W?
- About 16.7 A at 120 V; 8.3 A at 240 V.
- Can a microwave and kettle share a circuit?
- Only if the circuit is sized for both together.
- How many watts on a 15 A circuit?
- 1,800 W at 120 V (1,440 W continuous).
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.