Power converter

Model: Exact unit definitions

Accuracy: Exact to double precision: each conversion is one correctly rounded ratio of exact definitions

When to use this: Use this for any rating that has to cross systems: an engine or motor in horsepower against a limit in kilowatts, a generator or heater in watts, a pump curve quoted either way. Vehicle, aircraft and equipment ratings are published in whichever unit the market expects and compared against a specification in the other.

Limitations: The horsepower here is the mechanical one of 550 ft·lbf/s, which is what a US or UK rating means. The metric horsepower (PS or ch) is 735.49875 W, 1.4% smaller, and the boiler horsepower is about thirteen times larger; neither is offered, because a document that says only horsepower has to be read before it is converted rather than guessed at here. Power is a rate, not an amount: a kilowatt for an hour is a kilowatt hour, and the energy converter is the one for that.

Worked example: 180 hp in kilowatts. Source: Exact unit definitions (NIST SP 811 Appendix B). It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

Review: Not yet independently reviewed by a metrologist.

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Checked against: 22 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, National Institute of Standards and Technology, 2008 edition. Appendix B.8, Factors for units listed alphabetically.