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HP to Watts Calculator
Horsepower times 746 is the watts a motor delivers at the shaft. What it takes from the outlet is more — and on a small motor, a lot more.
Watts = hp × 746
Watts = hp × 746. 1 hp is 746 W; ½ hp is 373 W; ¾ hp is 559.5 W; 2 hp is 1,492 W. Metric horsepower (PS) is about 735.5 W.
That is mechanical output. A ½ hp single-phase motor at 115 V carries a full-load current of 9.8 A in NEC Table 430.248 — about 1,127 VA, three times the shaft watts. For larger motors in kilowatts, with efficiency and service factor, use the HP to kW calculator.
The horsepower
Fractions as decimals: ⅓ hp is 0.333, ¾ hp is 0.75.
The answer
Mechanical output
373.0 W
W = hp × 746.0 → 0.500 × 746.0
That is what the shaft delivers. The motor draws more than this from the outlet, because no motor is 100% efficient.
Common sizes in electrical hp
| hp | Watts at the shaft |
|---|---|
| ⅙ | 124.3 W |
| ¼ | 186.5 W |
| ⅓ | 248.7 W |
| ½ | 373.0 W |
| ¾ | 559.5 W |
| 1 | 746.0 W |
| 1½ | 1,119.0 W |
| 2 | 1,492.0 W |
| 3 | 2,238.0 W |
| 5 | 3,730.0 W |
What this does not tell you
Circuit sizing. NEC Article 430 sizes motor branch circuits from its full-load current tables by horsepower and voltage, not from a converted wattage. Starting draw. A motor starting across the line draws several times its running current for a moment. Efficiency and service factor for larger motors are on the HP to kW calculator.
Informational use only, please verify before you rely on it
This reproduces the standard definitions of electrical horsepower (746 W), mechanical horsepower (550 ft·lbf/s, about 745.7 W) and metric horsepower (about 735.5 W), the volts × amps product, and the single-phase full-load currents of NEC Table 430.248. It is a unit conversion and a comparison, not a determination. It does not measure a motor or size conductors, overcurrent protection or motor branch circuits, which NEC Article 430 governs. Confirm against the equipment nameplate and with the authority having jurisdiction.
This tool is provided for general informational and educational purposes only. Its output is an illustrative estimate generated from the values you enter and from general assumptions that will not match every deal, market, lender, or homeowner. It is not tax, legal, accounting, financial, or professional advice, and it is not a quote, an offer, a credit decision, or a guarantee of pricing, approval, timing, savings, or eligibility.
You are solely responsible for independently confirming all information presented here including any figures, rates, fees, margins, timelines, tax treatment, and federal, state, local, or utility incentives, with the applicable lender, authority having jurisdiction, and your own qualified tax, legal, and financial advisors before acting on it, relying on it, or presenting it to a homeowner or any third party. Incentive programs, lender terms, and permitting requirements change frequently and vary by jurisdiction.
Seamless Home is not a tax advisor, law firm, lender, or licensed installing contractor, and makes no representation or warranty as to the accuracy, completeness, or currency of the information produced by this tool. To the fullest extent permitted by law, Seamless Home accepts no liability for any decision made or action taken in reliance on it.
Why the watts and the amps disagree on a small motor
Horsepower is a rating of what the shaft delivers. Converting it to watts gives the same thing in electrical units, and it is the right number for comparing motors or reading a spec sheet written in the other unit. It is not what the motor takes from the supply.
Two things sit between the shaft and the outlet. Losses — heat in the windings and iron, friction — make the input watts larger than the output. Power factor makes the volt-amperes larger than the input watts, because part of the current in an AC motor sets up the magnetic field rather than doing work; see what power factor is. Fractional-horsepower single-phase motors show both effects most, which is why the current on the plate looks out of proportion to the horsepower. Convert that current with the amps to watts calculator and a power factor, or go the other way with watts to amps.
For a motor's circuit, the number that counts is neither the watts nor the horsepower but the full-load current from the NEC tables. For the energy a motor uses over a run, multiply its input — not its shaft watts — by the hours with the watts to kWh calculator.
Frequently Asked Questions
How do you convert hp to watts?+
Multiply horsepower by 746 for electrical horsepower: watts = hp × 746. For mechanical (imperial) horsepower use about 745.7, and for metric horsepower (PS) about 735.5. ½ hp is 373 W; 2 hp is 1,492 W.
How many watts is 1 hp?+
746 watts for electrical horsepower, about 745.7 W for mechanical horsepower and about 735.5 W for metric horsepower. They are three slightly different units; for US motor nameplates, 746 W is the figure to use.
How many watts is a ½ hp motor?+
373 watts at the shaft — that is what the motor delivers. It draws more than that from the outlet, because some of the input is lost as heat and, on AC, the current also carries a power-factor component. NEC Table 430.248 lists 9.8 A for a ½ hp single-phase motor at 115 V, which is about 1,127 volt-amperes.
Why is a small motor's current so much higher than hp × 746 ÷ volts?+
Because hp × 746 is output, and current follows input. Losses make the input watts larger than the output, and power factor makes the volt-amperes larger than the input watts. Small single-phase motors show the biggest gap: 1 hp is 746 W at the shaft, but NEC Table 430.248 lists 16 A at 115 V — about 1,840 VA.
Is hp to watts different from hp to kW?+
The arithmetic is the same — kilowatts are watts ÷ 1,000. This page works in watts for fractional and small motors and compares against full-load current; the HP to kW calculator works in kilowatts for larger motors and applies nameplate efficiency and service factor.
Can I use the watts to size a breaker or wire for a motor?+
No. NEC Article 430 sizes motor branch circuits from the full-load current tables (Table 430.248 for single-phase, 430.250 for three-phase) by horsepower and voltage — not from a converted wattage and not from nameplate current alone. A motor also draws several times its running current while it starts.
Is this a determination?+
No. It reproduces the standard definitions of horsepower and the volts × amps product as a preparation aid. It does not measure a motor, select equipment, or size conductors or overcurrent protection. Confirm against the nameplate and with the authority having jurisdiction.
Related resources
HP to kW Calculator
Larger motors in kilowatts, with efficiency and service factor applied.
Learn more →kW to HP Calculator
The inverse, in all three horsepowers.
Learn more →Amps to Watts Calculator
Real power from a current reading, with power factor.
Learn more →What Is Power Factor?
Why a motor's volt-amperes run above its watts.
Learn more →Ratings read the way the nameplate wrote them
Seamless Home runs the design, permit and interconnection layer for the partners it works with — which is where a motor or equipment rating gets read as the figure it actually is. Coverage is confirmed per service area rather than promised as blanket availability.
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