Confirm the circuit voltage
Use the actual voltage across the load. Do not assume 120V, 230V or 240V from the breaker appearance.
15 amp circuit capacity guide
How Many Watts Can a 15 Amp Circuit Breaker Handle?
A 15A breaker does not have one wattage value for every circuit. Voltage, phase, power factor, load duration, conductor conditions and local rules all affect the usable load.
Fast answer: at 120V, 15A equals 1,800VA. At 240V, it equals 3,600VA. For a common U.S. continuous-load planning basis, 12A gives 1,440VA at 120V or 2,880VA at 240V. Real watts may be lower when power factor is below 1.
120V nominal1,800VA at 15A
240V nominal3,600VA at 15A
Continuous loadOften planned at 12A in U.S. applications
Real powerVoltage x current x power factor
Photo: Bulat843 / Pexels
The direct answer
Start with voltage and load type, not the breaker number alone
The simple calculation is voltage multiplied by current. That result is volt-amperes, or VA. For a heater or another load with a power factor near 1, VA and watts are close. Motors, power supplies and other electronic loads can draw more current than a watt-only estimate suggests.
120V circuit1,800VA120V x 15A. Common continuous planning value: 1,440VA at 12A.
240V circuit3,600VA240V x 15A. Common continuous planning value: 2,880VA at 12A.
Power factorPF changes wattsAt PF 0.80, 1,800VA represents about 1,440W of real power.
Two-pole breakerStill 15AA two-pole 15A breaker provides 15A through both linked conductors. It is not a 30A breaker.
Read this before using the number
Four checks keep a simple calculation useful and safe
Separate continuous loads
A load expected to run for three hours or more may require a lower planning current or a larger circuit under the applicable rules.
Use input data for the load
Check nameplate current, power factor, efficiency and starting current. Output watts are not always the same as electrical input.
Verify the complete circuit
The conductor, terminals, receptacles, enclosure, ambient temperature and breaker must work as one coordinated path.
Interactive planning tool
Planning result
15 Amp Breaker Wattage Calculator
Calculate nominal apparent power and an estimated real-power value. Change the current if you need to review another breaker rating.
Calculated result
Nominal apparent power1,800 VA
Estimated real power1,800 W
Planning current12.0 A
Planning real power1,440 W
At 120V single-phase, a 15A circuit has 1,800VA of nominal capacity. With the selected 80% planning basis and PF 1.00, the planning value is about 1,440W.
Capacity by voltage
The same 15A rating produces different power at different voltages
The table separates simple single-phase arithmetic from balanced three-phase examples. Values assume power factor 1.00 so the real-power number is easy to compare.
| System example | Nominal formula | Nominal capacity | Common 80% planning current | Planning capacity at PF 1.00 |
|---|---|---|---|---|
| 120V single-phase | 120 x 15 | 1,800VA / about 1,800W | 12A | 1,440VA / about 1,440W |
| 208V single-phase | 208 x 15 | 3,120VA / about 3,120W | 12A | 2,496VA / about 2,496W |
| 230V single-phase | 230 x 15 | 3,450VA / about 3,450W | 12A | 2,760VA / about 2,760W |
| 240V single-phase | 240 x 15 | 3,600VA / about 3,600W | 12A | 2,880VA / about 2,880W |
| 208V balanced three-phase | 1.732 x 208 x 15 | About 5,404VA / 5,404W | 12A per phase | About 4,323VA / 4,323W |
| 400V balanced three-phase | 1.732 x 400 x 15 | About 10,392VA / 10,392W | 12A per phase | About 8,314VA / 8,314W |
These are comparison values, not permission to load a circuit to the number shown. Three-phase calculations assume a balanced load and line-to-line voltage. Apply the correct local code, equipment instructions, conductor limits and protection study.
Where simple watts stop being enough
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EV
Load behavior can change the current and trip risk
A circuit that looks acceptable from watts alone may still have high starting current, poor power factor, harmonic current or a long operating time. Use the load's electrical input data.
Resistive heating
Watts and VA are often close, but a heater may be a continuous load. A 1,500W heater on 120V draws about 12.5A before other loads are added.
Motors and compressors
Starting current can be several times the running current. Review nameplate current, starting method, trip curve and the applicable motor-circuit rules.
Electronic power supplies and UPS loads
Input power factor, efficiency, inrush and harmonics can matter. Do not size the circuit from output watts alone.
EV charging
EV supply equipment is commonly treated as a continuous load in U.S. practice. A 120V, 12A Level 1 load is about 1.44kW and uses a 15A branch-circuit basis only where the complete installation allows it.
VA, watts and power factor
Use the equation that matches the electrical system
VA describes voltage multiplied by current. Watts describe real power. Power factor links them in AC systems. This is why a 15A breaker cannot be converted to one universal wattage without knowing more.
Example: 1,200W at 120V and PF 0.80 requires about 12.5A. Dividing 1,200W by 120V alone would incorrectly suggest 10A.
Use voltage and current at the DC load. Confirm polarity and equipment ratings.
Use the actual power factor where it is known.
Use line-to-line voltage and per-phase current for a balanced load.
Add the 1.732 factor in the denominator for balanced three-phase AC.
Common mistakes
Avoid shortcuts that hide the real circuit limit
Treating 1,800W as a guaranteed target
That figure assumes 120V, 15A and PF 1.00. It does not include continuous-load treatment, derating or other connected loads.
Adding the poles together
A two-pole 15A breaker is still rated 15A through each linked pole. The higher 240V power comes from voltage, not 30A of current.
Using appliance output watts
For motors, chargers, UPS systems and power supplies, use the electrical input current or complete input data.
Ignoring other loads
The calculation applies to the whole branch circuit. Lighting, receptacles, controls and auxiliary loads all use capacity.
Upsizing the breaker to stop trips
A larger breaker can leave the conductor and devices underprotected. Find the trip cause before changing protection.
Assuming every country uses the same rule
Continuous-load treatment, conductor methods, permitted devices and approvals vary. Verify the authority and standard for the project.
Safety boundary
Stop using the circuit when warning signs appear
A calculation cannot diagnose a damaged breaker, loose connection, wet enclosure, overheated conductor or failing receptacle.
- Repeated breaker trips, buzzing, burning odor, discoloration or heat need investigation.
- Do not replace a 15A breaker with a larger rating unless a qualified person has verified and redesigned the complete circuit where required.
- Panel measurements and internal work expose hazardous energized parts. Use a qualified electrician or authorized technical professional.
For buyers, panel builders and OEM teams
Send enough information to match the breaker and circuit duty
A useful RFQ is more than “15A breaker.” Include the system and installation details that control the exact model.
Electrical systemAC or DC, voltage, frequency, phases, poles, neutral and earthing arrangement.
Load informationRunning current, real power, power factor, starting current, load type and operating duration.
Protection dutyProspective short-circuit current, required breaking capacity, trip curve or characteristic, and coordination objective.
InstallationDIN rail or panel arrangement, enclosure, ambient temperature, conductor data and terminal requirements.
Commercial scopeQuantity, destination market, required approval evidence, labels, packaging, sample and delivery expectations.
Continue the decision
Use the next page for the next engineering question
These SENTOP pages continue from basic power arithmetic to protection selection and product review.
Frequently asked questions
15 amp breaker capacity questions
How many watts can a 15 amp breaker handle at 120 volts?
The simple nominal result is 1,800VA because 120V x 15A = 1,800VA. That is about 1,800W only when power factor is near 1. For a common U.S. continuous-load planning basis, 12A gives 1,440VA or about 1,440W at PF 1.00.
How many watts can a 15 amp breaker handle at 240 volts?
The nominal single-phase result is 3,600VA. A common 80% continuous planning value is 2,880VA. Verify the two-pole arrangement, conductor, load type, local rules and equipment instructions.
Is a double-pole 15 amp breaker equal to 30 amps?
No. The linked poles open together, but the breaker remains 15A through each pole. In a 240V single-phase circuit, the power is higher because the load voltage is 240V.
Why should I use VA instead of watts first?
Voltage multiplied by current gives VA. Watts also depend on power factor in AC systems. Starting with VA prevents a poor-power-factor load from looking smaller than its actual current demand.
Can a 1,500 watt heater run on a 15 amp, 120 volt circuit?
A 1,500W resistive heater draws about 12.5A at 120V. That exceeds a 12A continuous planning value, and other loads make the situation worse. The final answer depends on operating time, the product instructions and the applicable circuit rules.
Why does a breaker trip below the calculated wattage?
Possible reasons include motor or power-supply inrush, poor power factor, other loads on the circuit, heat, loose connections, a damaged device, a short or earth fault, or a trip characteristic that does not match the load. Repeated trips need investigation.
Can I install a larger breaker to get more watts?
Not as a shortcut. The breaker must protect the conductor and circuit components. Increasing the breaker rating without verifying and redesigning the complete circuit can create a fire or shock hazard.
Technical references
Check the source that applies to your system and location
The arithmetic is universal. Installation permission is not. Use the adopted electrical code, equipment documentation and qualified design review.
- NIST: Watt - definition of power in the SI system.
- NIST: SI Units - Electric Current - relationship between volts, watts and amperes.
- NIST: Power and Energy Measurements - voltage, current and power-factor context.
- U.S. Department of Energy AFDC: EV charging guidance - 120V Level 1 example at 12A and 1.44kW.
- U.S. Department of Energy: EVSE infrastructure training - continuous-load branch-circuit examples.
- U.S. Consumer Product Safety Commission: 15A and 20A branch-circuit loads.
- Electrical Safety Foundation International: Do not overload your home - warning signs and overload prevention.
Need a 15A breaker reviewed for a real project?
Send voltage, poles, load type, running and starting current, breaking-capacity requirement, quantity, destination market and available drawings.
