How Many Watts Is 18 Amps at 240V?
18 amps at 240V equals 4,320 watts on an AC single-phase resistive circuit (PF 1.0). AC resistive at PF 1.0 and the DC baseline land on the same number at this voltage.
At 4,320W, this is equivalent to 4.32 kW. NEC 210.19(A) sizes the conductor and OCP at 125% of any continuous load (equivalently 80% of breaker rating), so the usable continuous capacity on this circuit is about 3,456W.
For comparison at the same inputs: 4,320W on DC. These are reference values for contrast; the canonical answer for this page is the one in the hero above.
Use this citation when referencing this page.
Assumes an AC single-phase resistive load at PF 1.0. Typing a commercial L-L voltage (208/400/480V) re-routes the result to three-phase; 277V stays on single-phase because it's the L-N lighting leg of a 480Y/277V wye; 12/24V re-routes to DC.
Formulas
DC: Amps to Watts
P(W) = I(A) × V(V)
AC Single Phase (PF = 0.85)
P(W) = PF × I(A) × V(V)
What Can You Run on 18A at 240V?
Appliances This Circuit Supports
A 18A circuit at 240V delivers 4,320W to a resistive AC load at PF 1.0. NEC 210.19(A) sizes the conductor and OCP at 125% of any continuous load (equivalently 80% of the breaker rating, about 3,456W here), so these appliances fit within the continuous-load allowance:
| Appliance | Watts | % of Circuit | Fits Continuous? |
|---|---|---|---|
| Air Conditioner (window) | 3,500W | 81.02% | Non-continuous only |
| Electric Oven | 2,500W | 57.87% | Yes |
Monthly Running Cost
As a rough reference, running 4,320W for 8 hours daily at the US residential average of $0.17/kWh works out to about $176.26 per month. Electricity rates change every tariff cycle and vary sharply by region, time of day, and utility; treat the number here as a ballpark and check your actual bill or the energy-cost calculator with your own rate for a real figure.
Standard Breaker Sizes Near 18A
This section is reference framing, not an install recommendation. NEC 240.6(A) lists the standard breaker amp ratings, and under the NEC 210.19(A) 125% continuous-load rule (equivalently 80% of breaker rating) a 18A non-continuous load maps to the 20A standard size at or above the load, and a continuous 18A load maps to 25A once the 125% factor is applied. Breaker ratings are expressed in amps, not watts: the real power associated with a given breaker size depends on the circuit type and the load's power factor, which is why the AC Conversion Detail section shows multiple wattage interpretations. None of these numbers is a breaker selection for a real install. Actual breaker and conductor selection depends on the equipment nameplate FLA, continuous-load treatment, conductor ampacity and termination temperature rating, bundling and ambient derates, any NEC 430/440 motor or HVAC provisions, and local code, and should be made by a licensed electrician against the specific install conditions.
AC Conversion Detail
On DC, 18A at 240V delivers a full 4,320W. On AC single-phase with a power factor of 0.85, the same current only delivers 3,672W of real power because the remaining capacity goes to reactive current.
| Circuit Type | Formula | Result |
|---|---|---|
| DC | 18 × 240 | 4,320 W |
| AC Single Phase (PF 0.85) | 0.85 × 18 × 240 | 3,672 W |
Power Output by Load Type
The same 18A circuit at 240V delivers different real power depending on the load, computed on the same single-phase basis the rest of the page uses:
| Load Type | PF | Real Power (18A at 240V, single-phase) |
|---|---|---|
| Resistive (heaters, incandescent) | 1 | 4,320 W |
| Fluorescent lamps | 0.95 | 4,104 W |
| LED lighting | 0.9 | 3,888 W |
| Synchronous motors | 0.9 | 3,888 W |
| Typical mixed loads | 0.85 | 3,672 W |
| Induction motors (full load) | 0.8 | 3,456 W |
| Computers (without PFC) | 0.65 | 2,808 W |
| Induction motors (no load) | 0.35 | 1,512 W |