Convert Milliwatts to BTU per Hour
Milliwatt (mW) to BTU per Hour (BTU/h) unit conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 mW = 0.0034121416 BTU/h
1 Milliwatt = 0.0034121416 BTU per Hour
1 BTU per Hour = 293.07107 Milliwatts
1 mW in every supported unit
Conversion chart: Milliwatt to BTU per Hour
Conversion table
| Milliwatt (mW) | BTU per Hour (BTU/h) |
|---|---|
| 0.01 mW | 3.41214E-05 BTU/h |
| 0.1 mW | 0.00034121416 BTU/h |
| 1 mW | 0.0034121416 BTU/h |
| 2 mW | 0.0068242833 BTU/h |
| 3 mW | 0.010236425 BTU/h |
| 5 mW | 0.017060708 BTU/h |
| 10 mW | 0.034121416 BTU/h |
| 20 mW | 0.068242833 BTU/h |
| 50 mW | 0.17060708 BTU/h |
| 100 mW | 0.34121416 BTU/h |
| 1000 mW | 3.4121416 BTU/h |
Milliwatt (mW)
Definition: One thousandth of a watt (10⁻³ W), a tiny unit of power used wherever the quantity of energy transferred per second is very small.
History: Introduced as a standard decimal-prefixed subdivision of the watt once the SI system of prefixes was formalized in the 20th century, following the same milli- convention used across other SI base and derived units.
Current use: Used to rate laser pointers, Bluetooth and Wi-Fi radio transmission power, LED indicator lights, and the tiny signal power levels found in telecommunications and consumer electronics.
BTU per Hour (BTU/h)
Definition: The rate of energy transfer equal to one British Thermal Unit (the heat needed to raise one pound of water by one degree Fahrenheit) per hour, equal to about 0.293 watts.
History: Derived from the British Thermal Unit, a 19th-century imperial heat-energy unit used throughout British and American engineering before the widespread adoption of the metric system's joule.
Current use: The standard unit for rating the heating and cooling capacity of air conditioners, furnaces, and boilers in the United States HVAC industry.
Supported Units
| Unit | Symbol | In Watts |
|---|---|---|
| Milliwatt | mW | 0.001 W |
| Watt | W | 1 W |
| Kilowatt | kW | 1000 W |
| Megawatt | MW | 1000000 W |
| Gigawatt | GW | 1E+09 W |
| Horsepower (mechanical) | hp | 745.69987 W |
| Horsepower (metric) | PS | 735.49875 W |
| BTU per Hour | BTU/h | 0.29307107 W |
| Foot-pound per Second | ft·lb/s | 1.3558179 W |
| Calorie per Second | cal/s | 4.1868 W |
About These Parameters
- Value
- The number you want to convert, expressed in the "From" unit. Accepts decimals.
- From Unit
- The unit your input value is currently measured in.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly.
How Power Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to the watt. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Milliwatt → BTU per Hour: multiply by 0.0034121416. For example, 1 mW × 0.0034121416 = 0.0034121416 BTU/h.
Mechanical vs. Metric Horsepower
The two horsepower units on this page look almost identical but are not quite the same: mechanical horsepower (hp) is defined as exactly 550 foot-pounds of work per second (about 745.7 W) and is the standard for cars and engines in the US and UK, while metric horsepower (PS, from the German Pferdestärke) is defined as the power to lift 75 kilograms one meter per second (about 735.5 W) and is used across continental Europe, Japan, and much of Asia. The difference is small — about 1.4% — but it means a car advertised as "300 PS" in Germany produces slightly less power than a car advertised as "300 hp" in the US, even though the numbers look the same.
How James Watt Defined Horsepower
In the 1780s, engineer James Watt needed a way to convince mill owners that his improved steam engines could outperform the horses they already used to turn grinding wheels. He observed a strong horse turning a mill and calculated it could sustain roughly 33,000 foot-pounds of work per minute — equivalent to 550 foot-pounds per second — and fixed that figure as "one horsepower." The unit stuck long after steam engines and horses both gave way to electric and internal combustion power, and it remains the standard way vehicle and engine power is marketed today.
Example
1 mW equals 0.0034121416 BTU/h. For scale, that's about 0× the power draw of a typical microwave oven (1,000 W, or 1000000 mW).
Frequently Asked Questions
How many BTU per Hour are in 1 Milliwatt?
1 Milliwatt (mW) equals exactly 0.0034121416 BTU per Hour (BTU/h).
Why are there two kinds of horsepower?
Mechanical horsepower (550 ft·lb/s, about 745.7 W) was defined in Britain by James Watt in the 1780s, while metric horsepower (PS, about 735.5 W) was defined later in continental Europe using kilograms and meters instead of pounds and feet. Both describe roughly "the power of a horse," but because they were defined with different unit systems the two figures differ by about 1.4%.
How many watts is 1 horsepower?
1 mechanical horsepower equals exactly 745.6998715823 watts (about 745.7 W), while 1 metric horsepower (PS) equals exactly 735.49875 watts (about 735.5 W). Both are close to but not the same as 1 kilowatt (1,000 W).
How accurate are these conversions?
Every conversion factor used here is the exact, internationally recognized value (e.g. 1 hp = exactly 745.6998715823 W, 1 PS = exactly 735.49875 W) — results are limited only by floating-point display precision, not by rounded conversion constants.