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kW to BTU/hr Calculator

Convert a metric kilowatt heating or cooling output into BTU per hour for specifying US equipment.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Equivalent output

11942.5 BTU/hr

High confidence

Converted using an exact defined factor of 3412.141633128 BTU/hr per kW. Manufacturers round nameplate figures heavily, so a 3.5 kW unit is usually sold as 12,000 BTU/h rather than the exact 11,942.

Conversion factor applied
3412.14 BTU/hr per kW

European and Australian equipment is rated in kilowatts while American catalogues, permits and rebate schedules still work in BTU per hour, so anyone specifying a US-market unit from a metric datasheet has to move between the two. The arithmetic is exact — a kilowatt is 3,412.14 BTU/h by definition — but the practical trap is rounding: the industry sells in nominal sizes, so a 3.5 kW output is marketed as a 12,000 BTU/h or one-ton unit even though the true conversion is 11,942 BTU/h. Specify against the nominal size the catalogue uses, and keep the exact figure for load calculations rather than for ordering. Note too that a heat pump's thermal output and its electrical draw are different numbers: converting the input power instead of the rated capacity will undersize the equipment by whatever its coefficient of performance happens to be.

Add the equipment this sizes

This result is a specification — 11,942.496 BTU/hr — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • 1 BTU/h is defined as 0.29307107017222 W (International Table), so 1 kW = 3412.1416 BTU/h
  • Nominal cooling tonnage: 1 ton of refrigeration = 12,000 BTU/h

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Frequently asked questions

Why does my 3.5 kW unit get sold as 12,000 BTU/hr rather than 11,942?
Because equipment is marketed in nominal sizes. 12,000 BTU/hr is one ton of refrigeration, a round catalogue size, and manufacturers group nearby outputs under it. Use the nominal figure when ordering and the exact one when doing load calculations — the difference is under half a percent and will not change the plant selection, but it will confuse a paperwork check if you quote a number nobody recognises.
Should I convert the electrical input or the rated output?
The rated thermal output. On a heat pump those are very different numbers: a unit drawing 1 kW of electricity can deliver 3–4 kW of heat, because it moves heat rather than making it. Converting the input figure would undersize the equipment by whatever the coefficient of performance is.
Is a BTU always the same size?
Not quite. Several BTU definitions exist and differ slightly. HVAC work uses the International Table BTU, which is what this calculator applies, at 0.29307107 W. The thermochemical BTU is about 0.05% smaller. The gap is irrelevant for equipment sizing but matters if you are reconciling against a scientific reference.