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Convert Watts to Foot-Pounds per Second - Power Converter

This converter converts power values expressed in kilowatts (kW) to foot‑pounds‑force per second (ft·lbf/s). A kilowatt is an SI-derived unit (1000 watts), and foot‑pound‑force per second is an imperial/engineering unit frequently used in mechanical contexts.

The conversion uses the energy equivalence between joules and foot‑pounds‑force together with the definition of the watt (1 W = 1 J/s). For routine calculations the result is presented with practical rounding, but exact factors are shown below for traceability.

If you depend on the result for measurement, procurement, or compliance, verify numeric formatting and instrument calibration against applicable standards and lab procedures before using the value in regulated work.

Updated Nov 14, 2025

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Methodology

Power in kilowatts is first expressed in watts (1 kW = 1000 W) and watts in joules per second (1 W = 1 J/s). The conversion to foot‑pounds‑force per second uses the exact energy equivalence between the joule and the foot‑pound‑force.

We use the internationally accepted constant for the joule to foot‑pound‑force relationship to compute a fixed conversion factor. This approach follows SI unit definitions and the unit‑equivalence practice recommended by national metrology institutes.

Accuracy notes: the numerical constant is given to many significant digits for traceability. For practical use, round to a sensible number of digits; for lab or legal metrology, follow the uncertainty statements and calibration procedures in ISO/IEC 17025 and national guidance.

Worked examples

Example 1: 0.5 kW → 0.5 × 737.5621492772662 ≈ 368.7810746 ft·lbf/s (round as needed).

Example 2: 10 kW → 10 × 737.5621492772662 ≈ 7375.621492772662 ft·lbf/s.

Further resources

Expert Q&A

What is the exact conversion factor between kW and ft·lbf/s?

Using the joule to foot‑pound‑force equivalence, 1 kW = 737.5621492772662 ft·lbf/s (this numeric value is produced from 1000 J/s divided by 1.3558179483314004 J per ft·lbf).

How many significant digits should I use?

For engineering estimates 4–6 significant digits are typically sufficient. For calibration, legal metrology, or published data, follow the uncertainty and rounding rules in ISO/IEC 17025 and your local metrology authority.

Does this conversion account for measurement uncertainty?

No. This converter provides a mathematical conversion using internationally referenced constants. Measurement uncertainty depends on the instruments and procedures used to measure power and should be evaluated separately against ISO/IEC 17025 guidance.

Are there safety or regulatory considerations when measuring power?

Yes. Work with electrical or rotating machinery must follow relevant safety standards and regulations, for example electrical safety rules and workplace protections specified by occupational safety authorities. Always de‑energize equipment and consult local regulations before taking measurements.

Why not convert through horsepower?

Converting kW → HP → ft·lbf/s is valid because horsepower definitions link to ft·lbf/s, but converting directly via joules yields a single, traceable numeric factor and avoids intermediate rounding steps.

Sources & citations