Amps to Watts Calculator
Power Output
1,800 Watts
15.00A × 120V = 1,800W
Amps
15.00 A
Voltage
120V
Max Safe Watts
1,440 W
Equivalent
A space heater or a hair dryer
Formula: Watts = Amps × Volts. Max safe watts follows the NEC 80% rule (continuous load ≤ 80% of circuit capacity).
Safety: Always consult a licensed electrician for circuit design. The NEC 80% rule limits continuous loads to 80% of breaker rating. Actual capacity depends on wire gauge, length, 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.
Amps to Watts Reference Table
| Amps | At 120V | At 240V | Safe Watts (120V) |
|---|---|---|---|
| 10A | 1,200W | 2,400W | 960W |
| 15A | 1,800W | 3,600W | 1,440W |
| 20A | 2,400W | 4,800W | 1,920W |
| 30A | 3,600W | 7,200W | 2,880W |
| 50A | 6,000W | 12,000W | 4,800W |
| 100A | 12,000W | 24,000W | 9,600W |
* Safe watts based on NEC 80% rule for continuous loads.
Common Circuit Capacities
| Circuit | Amps | Voltage | Max Watts |
|---|---|---|---|
| Standard Outlet | 15A | 120V | 1,800W |
| Kitchen / Bath | 20A | 120V | 2,400W |
| Dryer / Water Heater | 30A | 240V | 7,200W |
| Range / EV Charger | 50A | 240V | 12,000W |
How We Calculate
Our amps to watts calculator converts electrical current (amps) to power (watts) using the standard electrical formulas. The tool also calculates the maximum safe continuous wattage per the NEC 80% rule.
How the math works: For DC and single-phase AC: Watts = Amps × Volts. For three-phase AC: Watts = Amps × Volts × √3. Max safe watts = total watts × 0.8 (NEC 80% rule for continuous loads).
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. Provides twice the wattage of 120V for the same amperage.
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.
NEC 80% Rule Explained
The National Electrical Code requires that continuous loads (running 3+ hours) not exceed 80% of the circuit breaker rating. This provides a safety margin against overheating. For example, a 20A breaker can safely handle 16A continuously, or 1,920W at 120V. Non-continuous loads can use the full breaker rating.
Safety Note
Always consult a licensed electrician for circuit design and installation. Actual requirements depend on wire gauge, 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 amps to watts? +
Multiply amps by volts: Watts = Amps × Volts. For example, a 15-amp circuit at 120 volts provides 1,800 watts (15 × 120 = 1,800). For three-phase circuits, also multiply by √3 (1.732): Watts = Amps × Volts × √3.
How many watts is a 20-amp circuit? +
A 20-amp circuit at 120V provides 2,400 watts maximum (20 × 120 = 2,400). However, the NEC 80% rule limits continuous loads to 1,920 watts (2,400 × 0.8 = 1,920). At 240V, a 20-amp circuit provides 4,800 watts max (3,840W safe continuous).
How many watts is 15 amps at 120 volts? +
15 amps at 120 volts equals 1,800 watts (15 × 120 = 1,800). The safe continuous load is 1,440 watts (80% of 1,800W per NEC). This is the standard household circuit and can power a space heater, hair dryer, or several smaller appliances.
What is the NEC 80% rule? +
The National Electrical Code (NEC) limits continuous loads to 80% of the circuit breaker rating. A continuous load runs for 3+ hours. So a 20A breaker safely handles 16A continuously (20 × 0.8 = 16A), or 1,920W at 120V. This prevents overheating of wires and connections.
How many watts can a 30-amp 240V circuit handle? +
A 30-amp circuit at 240V provides 7,200 watts maximum (30 × 240 = 7,200). The safe continuous load is 5,760 watts (80% rule). Common 30A/240V appliances: electric dryers (5,000W), water heaters (4,500W), and small HVAC units.
What is the difference between amps and watts? +
Amps (amperes) measure electrical current — the flow of electrons through a wire. Watts measure power — the rate of energy use. They relate as: Watts = Amps × Volts. Think of water: amps is flow rate, volts is pressure, watts is total power delivered.
Why does voltage matter for the amps-to-watts conversion? +
Voltage determines how much power (watts) a given current (amps) delivers. Higher voltage means more watts for the same amperage. A 20A circuit at 120V provides 2,400W, while the same 20A at 240V provides 4,800W — twice the power. This is why heavy appliances use 240V circuits.
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