Watts to Amps Calculator
Current Draw
12.50 Amps
1,500W ÷ 120V = 12.50A
Watts
1,500 W
Voltage
120V
Breaker Size
20A
Wire Gauge
14 AWG
Formula: Amps = Watts ÷ Volts. Breaker size follows the NEC 80% rule (breaker ≥ 125% of load).
Safety: Always consult a licensed electrician for circuit design. Wire gauge and breaker recommendations are for general reference — actual requirements depend on wire length, conduit type, ambient temperature, and local codes.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Watts to Amps Reference Table
| Watts | At 120V | At 240V | Breaker (120V) |
|---|---|---|---|
| 500W | 4.17A | 2.08A | 15A |
| 1,000W | 8.33A | 4.17A | 15A |
| 1,500W | 12.50A | 6.25A | 20A |
| 2,000W | 16.67A | 8.33A | 25A |
| 3,000W | 25.00A | 12.50A | 40A |
| 5,000W | 41.67A | 20.83A | 60A |
* Breaker sizes based on NEC 80% rule for continuous loads.
Common Appliance Wattages
| Appliance | Watts | Voltage | Amps |
|---|---|---|---|
| Space Heater | 1,500W | 120V | 12.5A |
| Microwave | 1,200W | 120V | 10.0A |
| Electric Dryer | 5,000W | 240V | 20.8A |
| Central AC | 3,500W | 240V | 14.6A |
How We Calculate
Our watts to amps calculator converts electrical power (watts) to current (amps) using the standard electrical formulas. The tool also recommends breaker sizes and wire gauges per NEC guidelines.
How the math works: For DC and single-phase AC: Amps = Watts ÷ Volts. For three-phase AC: Amps = Watts ÷ (Volts × √3 × Power Factor). Breaker sizing follows the NEC 80% rule: breaker ≥ 125% of continuous load.
Common Voltage Standards
120V is standard US household voltage for outlets, lighting, and small appliances. Most residential circuits are 15A or 20A at 120V.
240V is used for heavy appliances like dryers, ranges, water heaters, and HVAC systems. Halves the current draw compared to 120V, allowing smaller wire gauge.
208V is common in commercial buildings with three-phase power. Used for commercial HVAC, kitchen equipment, and lighting panels.
277V / 480V are used in commercial and industrial settings for lighting, motors, and heavy machinery.
Wire Gauge Reference (NEC)
14 AWG: 15A max. 12 AWG: 20A max. 10 AWG: 30A max. 8 AWG: 40A max. 6 AWG: 55A max. 4 AWG: 70A max. Wire gauge requirements increase for long runs (50+ feet) to prevent voltage drop.
Safety Note
Always consult a licensed electrician for circuit design and installation. Actual requirements depend on wire length, conduit type, ambient temperature, number of conductors, and local building codes. This calculator provides general reference based on NEC guidelines.
Last updated: 2026-02-02
Frequently Asked Questions
How do you convert watts to amps? +
Divide watts by volts: Amps = Watts ÷ Volts. For example, a 1,500W space heater on a 120V circuit draws 12.5 amps (1500 ÷ 120 = 12.5). For three-phase circuits, also divide by √3 (1.732).
How many amps is 1,500 watts at 120V? +
1,500 watts at 120 volts = 12.5 amps. This requires a 15A or 20A circuit. A 15A breaker can handle 1,500W continuously (at 80% of 15A = 12A capacity), but a 20A circuit provides more headroom.
How many watts can a 20-amp circuit handle? +
A 20A circuit at 120V can safely handle 1,920 watts continuously (20A × 120V × 80% NEC rule = 1,920W). The maximum is 2,400W (20A × 120V) but the NEC limits continuous loads to 80% of breaker capacity.
What size breaker do I need? +
The NEC requires breakers rated at 125% of the continuous load. Calculate amps, multiply by 1.25, then round up to the next standard size (15A, 20A, 30A, 40A, 50A). Example: 16A load × 1.25 = 20A breaker.
What wire gauge do I need? +
Wire gauge depends on amperage: 15A uses 14 AWG, 20A uses 12 AWG, 30A uses 10 AWG, 40A uses 8 AWG, 50A uses 6 AWG. For runs over 50 feet, upsize one gauge to prevent voltage drop.
What is the difference between watts, amps, and volts? +
Watts measure power (how much energy is used). Amps measure current (flow of electricity). Volts measure electrical pressure (force pushing current). They relate as: Watts = Amps × Volts. Think of water: volts is pressure, amps is flow rate, watts is total power.
When should I use 240V instead of 120V? +
Use 240V for appliances drawing more than 15 amps at 120V (1,800W+). Common 240V appliances: electric dryers (5,000W), ranges (8,000–12,000W), water heaters (4,500W), HVAC units, and EV chargers. 240V halves the current, allowing smaller wire gauge.
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