Cernarus

Convert Watts to BTU/h – Power Converter

This converter converts electrical or thermal power measured in watts (W) to heating/cooling rate measured in British thermal units per hour (BTU/h). The relationship is a fixed unit conversion and is appropriate when you need a direct power-rate translation (one input, one output).

Use this tool for quick sizing checks, equipment comparisons, specification reading, and documentation where a power value needs to be expressed in BTU per hour. For energy over time (for example kWh or BTU total) use an energy calculator rather than this instantaneous power-rate converter.

This page highlights the conversion factor we apply, known small variations between BTU definitions, and recommended accuracy practices including traceability to national standards and instrument calibration guidance.

Updated Nov 30, 2025

Interactive Converter

Convert between watt and btu per hour with precision rounding.

Quick reference table

WattBTU per Hour
1 W3.41 BTU/h
5 W17.06 BTU/h
10 W34.12 BTU/h
25 W85.3 BTU/h
50 W170.61 BTU/h
100 W341.21 BTU/h

Methodology

We apply the internationally accepted conversion between SI power (watts) and BTU per hour using the joule definition of both units. The converter uses the commonly used factor where 1 watt ≈ 3.412142185 BTU/h, derived from the exact SI-Joule relationships.

Because BTU has historically had multiple closely related definitions (for example variations used in older tables or thermochemical vs international table values), small differences can appear at high precision. For regulatory, compliance, or contractual work, use the BTU definition specified in your applicable standard or test procedure.

For measurement and reporting traceability, follow calibration and uncertainty practices consistent with NIST guidance and ISO/IEC 17025 accredited laboratory procedures. For electrical power measurement best practices, consult relevant IEEE standards.

Worked examples

100 W → 341.2142185 BTU/h

5000 W → 17060.710925 BTU/h

0.75 W → 2.55910663875 BTU/h

Key takeaways

This converter performs a fixed unit conversion from watts to BTU per hour using the widely adopted factor 1 W ≈ 3.412142185 BTU/h.

For routine comparisons and specifications the provided factor is appropriate. For legal, contractual, or high-precision laboratory work, confirm the required BTU definition, include uncertainty, and use traceable, calibrated instrumentation.

Further resources

Expert Q&A

Why are there slight differences in conversion factors I’ve seen elsewhere?

Small variations stem from different historical definitions of the BTU (for example international table vs older thermochemical conventions) and from rounding. For high-precision work, confirm the BTU variant required by your specification and use a factor consistent with that definition.

How many significant digits should I use?

For general use, 3–6 significant figures are typically sufficient. For laboratory or contractual measurements, follow the significant-figure and uncertainty requirements of the applicable standard or test method and include measurement uncertainty alongside any reported value.

Does this convert energy (like kWh) to BTU?

No. This converter translates instantaneous power (watts) to a rate (BTU per hour). To convert energy (for example kilowatt-hours to BTU), use an energy conversion where 1 kWh = 3412.142 BTU (approx).

How do I ensure my measurements are compliant and traceable?

Use instruments calibrated to a national standard (NIST traceability in the U.S. or an equivalent national metrology institute). Maintain calibration certificates and follow ISO/IEC 17025-accredited lab practices for test procedures and uncertainty reporting.

Are there safety or regulatory considerations when using converted values for equipment sizing?

Yes. Always verify that converted values meet the safety margins, regulatory limits, and local codes applicable to heating, ventilation, air conditioning, and electrical installations. Where required, consult a licensed engineer and applicable OSHA, local building, or electrical codes.

Sources & citations