Watts to Amps Calculator
Convert power to current instantly. Essential for circuit breaker sizing, fuse selection, and electrical safety.
NEC-Referenced — Updated 2026(No Ohms needed! Wattage already accounts for resistance. Use for heaters & lights.)
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Homeowner Savings Tip: The "Heater Hazard" Savings
Running a 1,500W space heater on a 15A circuit draws 12.5 Amps. This exceeds the NEC 80% safety limit (12A). Not only is this a fire risk, but a loose connection on an overloaded circuit increases electrical resistance, literally wasting money as heat in your walls. Switch to a 20A dedicated circuit to stay safe and efficient.
How to Convert Watts to Amps
Converting watts to amps is one of the most critical calculations in electrical work. Whether you're selecting a fuse, sizing a wire, understanding generator capacity, or ensuring electrical safety, this calculation is foundational.
Example: 300W solar on 24V = 12.5A
For: batteries, solar panels, DC motors, automotive
Example: 1,200W heater on 120V, PF=1.0 = 10A
For: most residential homes, standard outlets
Example: 3,000W at 480V, PF=0.9 = 4.0A
For: commercial, industrial, large HVAC systems
How it Works: Safety & The 80% Rule
Understanding amperage isn't just about calculation — it's about electrical safety. The most important safety principle in US electrical code is the NEC 80% Continuous Load Rule.
The NEC 80% Continuous Load Rule
Why the 80% Rule Exists
Electrical components generate heat when carrying current. When a circuit runs at full rated capacity continuously, that heat accumulates and can cause insulation degradation, nuisance tripping, or — in worst cases — electrical fires. The 80% rule provides a thermal safety margin.
Safe: 1,200W Microwave on 20A Circuit
1,200W ÷ 120V = 10A. That's 50% of a 20A circuit — well within the 80% limit (16A).
Borderline: 1,500W Heater on 15A Circuit
1,500W ÷ 120V = 12.5A. That's 83% of a 15A circuit — above the NEC 80% rule for continuous operation.
Dangerous: 2,000W Appliance on 15A Circuit
2,000W ÷ 120V = 16.7A. Exceeds the 15A breaker's rated capacity — immediate fire and equipment hazard.
Wire Gauge & Amperage
Your wire gauge must match your circuit's amperage. Undersized wiring overheats — even if the breaker doesn't trip. Always verify wire gauge before adding high-draw appliances.
| Wire Gauge (AWG) | Max Amperage | Typical Circuit | Common Uses |
|---|---|---|---|
| 14 AWG | 15A | 15A breaker | Lights, outlets, fans |
| 12 AWG | 20A | 20A breaker | Kitchen, bathroom circuits |
| 10 AWG | 30A | 30A breaker | Dryers, water heaters, EV Level 2 |
| 8 AWG | 40A | 40A breaker | Electric ranges, large A/C |
| 6 AWG | 55A | 50A breaker | EV fast charging, hot tubs |
Appliance Amperage Table
Use this reference table to quickly look up the amperage of common household and commercial appliances at standard US voltages (120V and 240V).
| Appliance | Watts (W) | Voltage (V) | Amps (A) | Circuit Recommendation |
|---|---|---|---|---|
| LED Bulb | 10W | 120V | 0.08A | Any circuit |
| Phone Charger | 20W | 120V | 0.17A | Any circuit |
| Laptop | 65W | 120V | 0.54A | Any circuit |
| Television (LED 55") | 120W | 120V | 1.0A | Any 15A circuit |
| Desktop Computer | 300W | 120V | 2.5A | Any 15A circuit |
| Refrigerator | 150W | 120V | 1.25A | Dedicated 15–20A |
| Microwave (1,000W) | 1,000W | 120V | 8.3A | Dedicated 20A |
| Toaster | 900W | 120V | 7.5A | 15A circuit |
| Coffee Maker | 1,000W | 120V | 8.3A | 15A circuit |
| Hair Dryer | 1,800W | 120V | 15.0A | Dedicated 20A |
| Space Heater | 1,500W | 120V | 12.5A | Dedicated 20A |
| Window A/C (small) | 1,200W | 120V | 10.0A | 15–20A circuit |
| Dishwasher | 1,800W | 120V | 15.0A | Dedicated 20A |
| Washing Machine | 500W | 120V | 4.2A | Dedicated 20A |
| Electric Clothes Dryer | 5,000W | 240V | 20.8A | Dedicated 30A |
| Electric Water Heater | 4,500W | 240V | 18.75A | Dedicated 30A |
| Electric Range/Oven | 12,000W | 240V | 50.0A | Dedicated 50–60A |
| Central A/C (3-ton) | 3,500W | 240V | 14.6A | Dedicated 30A |
| EV Charger (Level 2) | 7,200W | 240V | 30.0A | Dedicated 40–50A |
| Hot Tub / Spa | 6,000W | 240V | 25.0A | Dedicated 50A GFCI |
Table assumes resistive loads (PF = 1.0). Motor loads and compressors will draw slightly more current due to inductive power factor.
Frequently Asked Questions
Common questions about watts-to-amps conversion, circuit safety, and electrical sizing.
How do I convert watts to amps? ▾
Divide watts by volts: Amps = Watts ÷ Volts. For a 1,200W appliance on a 120V circuit, that's 1,200 ÷ 120 = 10 amps. This applies to DC circuits and resistive AC loads. For AC inductive loads, divide by (Volts × Power Factor).
What is the formula for watts to amps? ▾
For DC and resistive AC loads: A = W ÷ V. For single-phase AC inductive loads: A = W ÷ (V × PF), where PF is the power factor. For three-phase AC: A = W ÷ (√3 × V × PF).
What is the NEC 80% rule? ▾
The National Electrical Code (NEC 210.20) states that a circuit breaker should never carry more than 80% of its rated amperage for continuous loads (loads lasting 3+ hours). A 20A breaker's safe continuous limit is 16A; a 15A breaker's limit is 12A.
How many amps does a 1500W heater draw? ▾
On a 120V circuit: 1,500 ÷ 120 = 12.5 amps. On a 240V circuit: 1,500 ÷ 240 = 6.25 amps. The 120V version exceeds the NEC 80% safe limit for a 15A circuit (12A), so a dedicated 20A circuit is recommended.
How many amps does a 2000W appliance use? ▾
On 120V: 2,000 ÷ 120 = 16.7 amps — this requires a dedicated 20A circuit. On 240V: 2,000 ÷ 240 = 8.3 amps — comfortably within a 15A circuit. This is why large appliances like dryers and ranges use 240V.
Can I run a 1800W hair dryer on a 15A circuit? ▾
Technically yes — 1,800W ÷ 120V = 15A, which exactly matches a 15A breaker. However, the NEC 80% rule limits continuous loads to 12A (1,440W), so a 1,800W hair dryer approaches the danger zone on a 15A circuit, especially if other devices share it.
What's the difference between amps and watts? ▾
Watts (W) measure power — the rate of energy consumption. Amps (A) measure current — the rate of electrical charge flow. They're related by voltage: W = A × V. Your electric bill is in kilowatt-hours (kWh), which is watts × hours ÷ 1,000.
How many amps does a microwave use? ▾
A typical 1,000–1,200W microwave on 120V draws 8.3–10 amps. A 1,500W microwave draws 12.5 amps — near the 80% limit for a 15A circuit. Most kitchens have dedicated 20A microwave circuits per NEC code.