swap_horiz Looking to convert 150A at 120V back to watts?

How Many Amps Is 18,000 Watts at 120V?

18,000 watts equals 150 amps at 120V 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 150A, the NEC 210.19(A) continuous-load sizing math (125% of the load, equivalently 80% of the breaker rating) points to a 200A breaker as the smallest standard size that covers this load continuously. A 150A breaker is the smallest standard size the raw current fits under, but it is non-continuous-only at this load.

18,000 watts at 120V

150 Amps

18,000 watts equals 150 amps at 120 volts (AC single-phase, PF 1.0 resistive)

DC150 A

Try: 20,000W at 120V 15,000W at 120V 10,000W at 120V 8,000W at 120V

Watts

Volts

Amps (AC 1Φ, PF 1.0)

150

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: Watts to Amps

I_(A) = P_(W) ÷ V_(V)

18,000 ÷ 120 = 150 A

AC Single Phase (PF = 0.85)

I_(A) = P_(W) ÷ (PF × V_(V))

18,000 ÷ (0.85 × 120) = 18,000 ÷ 102 = 176.47 A

Circuit Sizing

Breaker Sizing

NEC 240.6(A) standard ampere ratings for branch-circuit and feeder breakers start at 15, 20, 25, 30, 35, 40, 45, and 50A and continue at 60A and above for feeder and large-appliance circuits. At 150A, the smallest standard breaker the raw current fits under is 150A, but that breaker only covers 150A non-continuously; NEC 210.19(A) requires conductor and OCP sized at 125% of any continuous load (equivalently 80% of breaker rating), so for a continuous load the smallest compliant breaker is 200A. Final selection still depends on the equipment nameplate, whether the load is continuous, conductor ampacity, and local code.

Breaker Size	Max Continuous Load (80%)	Status for 150A
90A	72A	Too small
100A	80A	Too small
110A	88A	Too small
125A	100A	Too small
150A	120A	Non-continuous only
175A	140A	Non-continuous only
200A	160A	OK for continuous
225A	180A	OK for continuous
250A	200A	OK for continuous
300A	240A	OK for continuous

Energy Cost

Running 18,000W costs approximately $3.06 per hour at the US average rate of $0.17/kWh (rates last reviewed April 2026). That is $24.48 for 8 hours or about $734.40 per month. See detailed cost breakdown.

AC Conversion Detail

The DC baseline for 18,000W at 120V is 150A. On an AC circuit with a power factor of 0.85, the current rises to 176.47A because reactive current flows alongside the real-power current.

Circuit Type	Formula	Result
DC	18,000 ÷ 120	150 A
AC Single Phase (PF 0.85)	18,000 ÷ (120 × 0.85)	176.47 A

Power Factor Reference

Power factor is the main reason 18,000W draws more current on AC than DC. At PF 1.0 (pure resistive, like a heater), the load pulls 150A at 120V on the single-phase basis the rest of the page uses. At PF 0.80 (typical induction motor), the same 18,000W pulls 187.5A. That is an extra 37.5A just to overcome the reactive component. Use the typical values below as a starting point, not for precise engineering calculations.

Load Type	Typical PF	18,000W at 120V (single-phase)
Resistive (heaters, incandescent)	1	150 A
Fluorescent lamps	0.95	157.89 A
LED lighting	0.9	166.67 A
Synchronous motors	0.9	166.67 A
Typical mixed loads	0.85	176.47 A
Induction motors (full load)	0.8	187.5 A
Computers (without PFC)	0.65	230.77 A
Induction motors (no load)	0.35	428.57 A

Same Wattage, Other Voltages

bolt18,000W at 24V = 750ADC bolt18,000W at 208V = 58.78A3Φ per line, PF 0.85 bolt18,000W at 220V = 81.82A1Φ, PF 1.0 bolt18,000W at 230V = 78.26A1Φ, PF 1.0 bolt18,000W at 240V = 75A1Φ, PF 1.0 bolt18,000W at 400V = 30.57A3Φ per line, PF 0.85 bolt18,000W at 460V = 26.58A3Φ per line, PF 0.85 bolt18,000W at 480V = 25.47A3Φ per line, PF 0.85 bolt18,000W at 575V = 21.26A3Φ per line, PF 0.85

swap_horiz 150A to watts at 120V payments 18,000W running cost cable Wire size for 150A at 120V electrical_services 18 kW to amps science Ohm's law: 120V & 150A functions Watts to amps formula

Other Wattages at 120V

Watts	AC 1Φ Amps PF 1.0 resistive	AC 1Φ Amps PF 0.85 motor
1,600W	13.33A	15.69A
1,700W	14.17A	16.67A
1,800W	15A	17.65A
1,900W	15.83A	18.63A
2,000W	16.67A	19.61A
2,200W	18.33A	21.57A
2,400W	20A	23.53A
2,500W	20.83A	24.51A
2,700W	22.5A	26.47A
3,000W	25A	29.41A
3,500W	29.17A	34.31A
4,000W	33.33A	39.22A
4,500W	37.5A	44.12A
5,000W	41.67A	49.02A
6,000W	50A	58.82A
7,500W	62.5A	73.53A
8,000W	66.67A	78.43A
10,000W	83.33A	98.04A
15,000W	125A	147.06A
20,000W	166.67A	196.08A

Frequently Asked Questions

How many amps is 18,000W at 120V? expand_more

18,000W at 120V draws 150 amps on AC single-phase at PF 1.0 (resistive). For comparison at the same voltage: 150A on DC, 176.47A on AC single-phase at PF 0.85. Actual current depends on the load's power factor.

Why does AC draw more amps than DC for 18,000W? expand_more

AC circuits with reactive loads have a power factor below 1.0, so they draw extra current. At PF 0.85, 18,000W at 120V draws 176.47A instead of 150A (DC). That is about 18% more current for the same real power.

Should I run 18,000W on a 15A circuit or a 20A circuit? expand_more

At 150A the load sits past the 80% continuous-load figure of a 120V/20A circuit (1,920W). A dedicated 240V circuit is the practical option for sustained operation.

Can I plug a 18,000W appliance into a standard 120V outlet? expand_more

No. 18,000W on 120V draws more than a 20A circuit can sustain. A dedicated 240V circuit is the practical option.

Why does a 18,000W resistive heater draw fewer amps than a 18,000W motor at 120V? expand_more

Resistive loads like space heaters and toasters have a power factor of 1.0, so 18,000W at 120V on a single-phase AC basis draws 150A. An induction motor at the same wattage has a PF around 0.80, drawing 187.5A on the same basis. The extra current is reactive, it does no real work but still has to flow through the conductors and breaker.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.