Watts (W) are the SI unit of power, representing the rate at which energy is transferred or converted. In electrical and mechanical engineering, watts are used to specify the output of engines, the consumption of devices, and the capacity of power supplies.
BTU per hour (BTU/hr) is a traditional unit of power used primarily in the United States for heating, ventilation, and air‑conditioning (HVAC) applications. One British Thermal Unit (BTU) is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit; when expressed per hour, it describes a continuous heat‑transfer rate.
Practical use of watts: rating of electric motors, LED lighting, solar panel output, and any device where electrical power is measured.
Practical use of BTU/hr: sizing furnaces, air‑conditioners, water heaters, and other thermal equipment.
The exact conversion factor is:
\\((1\\,\\text{W}=3.4121424501230075\\,\\text{BTU/h})\\)
This relationship lets engineers move seamlessly between metric and imperial power specifications.
Watt to BTU per hour Conversion Reference Table
Watt (W)
BTU per hour (BTU/hr)
0.1
0.3412
0.5
1.7061
1.0
3.4121
2.0
6.8243
5.0
17.0607
10.0
34.1214
20.0
68.2428
50.0
170.6071
100.0
341.2142
500.0
1706.0712
1000.0
3412.1425
Step‑by‑step conversion example
Convert 10 W to BTU per hour.
Identify the conversion factor: \\((1\\,\\text{W}=3.4121424501230075\\,\\text{BTU/h})\\)
Multiply the power in watts by the factor.
\\[10\\,\\text{W}\\times3.4121424501230075=34.121424501230075\\,\\text{BTU/h}\\]
Round to a sensible number of significant figures (typically three for engineering work):
34.1 BTU/hr.
BTU/hr remains common in the U.S. because many legacy standards, product specifications, and building codes were written before the metric system was widely adopted. Converting to watts is straightforward with the factor 3.4121424501230075, so engineers can work in either system without loss of accuracy.
The factor is exact based on the definition of the BTU (1 BTU = 1055.05585262 J) and the watt (1 W = 1 J/s). For most engineering applications, using 3.412 or 3.41 is sufficient; the extra digits only matter in high‑precision scientific work.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)