Amp Calculator
Calculate current draw and recommended breaker size
Total power of the device or load
Circuit voltage (120V or 240V)
Recommended Breaker
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amps
Amps
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amps
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Sizing breakers correctly prevents nuisance trips and fire hazards. Our calculator recommends the next standard breaker size above your calculated load.
- Find the wattage on the device nameplate or manual
- Enter the circuit voltage (120V or 240V)
- Review calculated amps and recommended breaker
- Match wire gauge to breaker size per NEC tables
Expert Insights
Smart analysis for your Electrical project
Breaker Sizing Standards
Standard breaker sizes are 15, 20, 30, 40, and 50 amps. AI rounds up to the next standard size and flags when upsizing is needed.
80% Continuous Load Rule
Continuous loads (3+ hours) must not exceed 80% of breaker rating. AI applies this rule automatically for heaters, EV chargers, and lighting.
Wire Gauge Matching
14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A. AI cross-references breaker size to ensure your wire is code-compliant.
Calculation Formula
Amps = Wattage / Voltage
Recommended Breaker = next standard size above Amps
(Standard sizes: 15, 20, 30, 40, 50 amps)
Breaker & Wire Size Reference
| Breaker Size | Wire Gauge | Max Continuous Load | Max Total Load | Common Use |
|---|---|---|---|---|
| 15A | 14 AWG | 12A (1,440W) | 1,800W | Lighting, outlets |
| 20A | 12 AWG | 16A (1,920W) | 2,400W | Kitchen, garage |
| 30A | 10 AWG | 24A (5,760W) | 7,200W | Dryer, water heater |
| 40A | 8 AWG | 32A (7,680W) | 9,600W | Range, EV charger |
| 50A | 6 AWG | 40A (9,600W) | 12,000W | Large range, subpanel |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- National Fire Protection Association (NFPA) — NFPA 70 — National Electrical Code (NEC), Article 240 — Overcurrent Protection. Learn more
- Underwriters Laboratories (UL) — UL 489 — Molded-Case Circuit Breakers. Learn more
- National Electrical Manufacturers Association (NEMA) — Circuit Breaker Standards. Learn more
Frequently Asked Questions
How do I calculate amps from watts?
Divide watts by volts: amps = watts / voltage. For example, 1800 watts at 120V equals 15 amps.
What size breaker do I need for a 1500W heater?
A 1500W heater at 120V draws 12.5 amps. A 15-amp breaker is the minimum, but a 20-amp circuit with 12 AWG wire is recommended for safety margin.
Why does my breaker keep tripping?
Breakers trip when current exceeds their rating. Common causes include overloaded circuits, short circuits, or a failing breaker. Reduce the load or add a dedicated circuit.