Mechanical horsepower to Watts Calculator

Direct answer

Multiply the entered mechanical horsepower value by 745.699872 to express it in watts (W). This converts mechanical horsepower (hp) to watt (W) within the documented power family.

Variables and formula

• Mechanical horsepower (hp): the source value measured in mechanical horsepower.
• Watts (W): the same quantity expressed in watt.
• Conversion factor: 745.699872 watts per mechanical horsepower.

Watts = Mechanical horsepower × 745.699872

The generator emits numeric factors with at most 15 significant digits. Calculator results keep up to 10 significant digits for display; this formatting does not increase the precision of the measurement.

Unit definitions and named variants

Source unit: mechanical horsepower (hp). Mechanical horsepower in this family is 550 international foot-pounds-force per second. With standard gravity, the exact chain gives approximately 745.699871582270 W. Named variant used: Mechanical horsepower (550 ft·lbf/s); not metric, electric, boiler, water, or nominal manufacturer horsepower. Reference: National Institute of Standards and Technology: NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically; National Institute of Standards and Technology: NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement.

Target unit: watt (W). The watt is the coherent SI unit of power: 1 W = 1 J/s = 1 kg·m²·s⁻³. The canonical watt definition is used; no alternate named variant is implied. Reference: Bureau International des Poids et Mesures: The International System of Units (SI), 9th edition, version 4.01.

The hp-to-W direction remains inside the power quantity; it changes the unit label and numerical scale, not the kind of quantity being measured.

Relationship and precision

This route uses at least one deliberately preserved rounded factor. Treat the displayed factor as an approximation at the precision documented below.

• hp relationship: The preserved baseFactor 745.699872 W is rounded from about 745.699871582270 W, a difference of about 4.18×10⁻⁷ W per hp.
• W relationship: The base factor is exactly 1 by the family base-unit choice.

To audit the factor through the family base unit, divide the raw dataset factors 745.699872 by 1. The generator emits that quotient once at 15 significant digits as the canonical direct factor 745.699872; runtime calculations do not divide the already-emitted base factors again.

Reproducible example

For 10 mechanical horsepower, 10 × 745.699872 = 7456.99872 watts. Repeating the same multiplication with the stated factor reproduces the displayed conversion before interface rounding.

Directional scale check

Because one mechanical horsepower contains 745.699872 watts, the target number is larger than the source number for every positive input. Zero maps to zero, while negative inputs are rejected because this family models non-negative magnitudes.

Interpretation

Read the result as watts, not mechanical horsepower. A value entered as hp leaves the calculator labelled W; this directional distinction matters even when the two units describe the same power quantity.

Assumptions and limitations

• Only non-negative power magnitudes are accepted; direction of power flow requires a signed model.
• Btu per hour means International Table Btu per hour (Btu_IT/h), not a thermochemical or other Btu variant.
• This family converts non-negative power magnitudes; it does not compute energy use without a duration or model signed import/export.

Common mistakes

• Metric horsepower is approximately 735.4988 W and is not this unit.
• The symbol is upper-case W because the unit name derives from a proper name.

Continue within the Power family

See the Power conversion hub for its five-unit reference table and all 20 directed routes.

• Reverse the direction: Watts to Mechanical horsepower
• Compare another power route: Mechanical horsepower to Kilowatts
• Compare another power route: Mechanical horsepower to Megawatts
• Compare another power route: Mechanical horsepower to International Table Btu per hour
• Compare another power route: Watts to Kilowatts

Assumptions

• The entered value uses mechanical horsepower exactly as labelled.
• Only non-negative power magnitudes are accepted; direction of power flow requires a signed model.
• Rounding and measurement uncertainty remain the user's responsibility.

Sources and methodology

CalcMotive publishes the formula and assumptions so you can decide whether the estimate fits your use case. See our methodology standards.

• The International System of Units (SI), 9th edition, version 4.01; Bureau International des Poids et Mesures; accessed Aug 7, 2026
• NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically; National Institute of Standards and Technology; accessed Aug 7, 2026
• NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement; National Institute of Standards and Technology; accessed Aug 7, 2026