SettingsSettings for this calculationUS
The current the appliance or circuit draws, in amps.
Use the running current from the nameplate, not the breaker rating. A 15 A breaker protects the wiring; it does not tell you what the connected load actually draws.
Power
1,800 W
P = V × I at 120 V single phase, with a power factor of 1 assumed. Assumes a resistive load. For motors and other inductive loads, multiply by the power factor to get real power.
- Conversion factor applied
- 120 W per A
They open the calculator with your figures already in it
Amps to Watts Calculator (120 V): 1,800 W — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Ohm's law for real power on a resistive single-phase load: P = V x I
- US residential general-purpose branch circuits are nominally 120 V
Inputs used
- Current (A)
- 15
Intermediate steps
- Conversion factor applied
- 120 W per A
Confidence note: P = V × I at 120 V single phase, with a power factor of 1 assumed. Assumes a resistive load. For motors and other inductive loads, multiply by the power factor to get real power.
What this calculation does not cover
- Assumes a power factor of 1, so what it really produces is volt-amps. A motor, compressor or switch-mode supply turns less of that into work — real watts are the volt-amps multiplied by the power factor — and a single current figure gives the calculator no way to tell which kind of load you entered.
- Uses the nominal 120 V, not your measured supply. Delivered voltage moves within a tolerance band and sags further along a loaded branch circuit, so a supply sitting a few percent off 120 V shifts the answer by the same proportion.
- This is not a load calculation and is not a basis for sizing a conductor or an overcurrent device. It applies no continuous-load allowance, no demand or diversity factors, and no derating for ambient temperature or conduit fill. Cable and protection are sized from current against the applicable code tables, not from this wattage.
- 120 V single-phase only. Feeding it the current of a 240 V split-phase appliance — range, dryer, water heater — returns half the real power, and three-phase equipment follows a different relationship carrying an additional root-three term.
- Steady running current only. Motor starting surge is several times this figure and is not represented, and the result is a rate rather than a quantity of energy — getting kWh needs the running hours as well.
Add the equipment this sizes
This result is a specification — 1,800 W — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- Ohm's law for real power on a resistive single-phase load: P = V x I
- US residential general-purpose branch circuits are nominally 120 V
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Working out what a circuit is actually carrying starts with a current figure and a supply voltage, and on a US general-purpose branch circuit that voltage is nominally 120 V. Multiplying the two gives apparent power, and for a heater, kettle or incandescent lamp that is also the real power. The distinction matters as soon as a motor is involved: an inductive load draws current that is partly out of phase with the voltage, so the volt-amps exceed the watts by the reciprocal of the power factor. A compressor pulling 15 A at 120 V presents 1,800 VA to the supply but may only be doing 1,440 W of work. Size conductors and breakers from current, which is what actually heats the cable, and use the wattage for energy and heat-gain calculations rather than for protection.