You've found a heater rated at 30 Btu per second. Your electrician, your utility bill, and every appliance plug in your building speak watts. Until you translate between the two, you're comparing apples to circuit breakers.
This guide closes that gap. You'll learn what each unit means, why they belong to the same family of measurement, and exactly how to move between them with confidence.
What Is a British Thermal Unit Per Second?
A British Thermal Unit (Btu) measures energy. Specifically, it's the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit.
Add "per second" and the unit changes jobs. It now measures power, which is the rate at which energy moves or gets used. One Btu per second means enough energy flows each second to warm one pound of water by one degree Fahrenheit.
Where You'll See Btu/s
The Btu comes from the imperial measurement tradition, so it dominates in the United States and parts of the UK. Engineers use Btu per second when sizing boilers, furnaces, chillers, and other heat-moving equipment where large, fast energy transfers are involved.
One thing to watch: many consumer product labels list Btu per hour instead of per second. Always check the time unit before you calculate anything.
What Is a Watt?
The watt (W) is the international standard unit of power. One watt equals one joule of energy transferred per second. It's named after James Watt, the Scottish engineer whose improvements to the steam engine helped launch the Industrial Revolution.
Watts describe almost everything electrical. Light bulbs, laptops, motors, solar panels, and your monthly electricity usage all get measured in watts or kilowatts (1,000 watts).
How Btu/s and Watts Relate
Here's the key insight: Btu per second and watts measure the exact same thing. Both express power. They simply come from different measurement systems, one rooted in thermal science and the other in electrical engineering.
The bridge between them is well established. One Btu corresponds to roughly 1,055 joules of energy. Since a watt is one joule per second, moving one Btu every second works out to approximately 1,055.06 watts.
In other words, 1 Btu/s is a little over one kilowatt. That single relationship unlocks every conversion you'll ever need between these two units.
How to Convert Btu/s to Watts (Step by Step)
The math takes seconds once you know the multiplier:
- Start with your Btu/s value. Grab it straight from the spec sheet or calculation.
- Multiply by 1,055.06. This converts the rate into watts.
- Label the result in W. For large numbers, divide by 1,000 to express it in kilowatts (kW).
Example: A boiler transfers heat at 8 Btu/s. Multiply 8 × 1,055.06 to get 8,440.45 W, or about 8.44 kW.
Going the other direction? Divide watts by 1,055.06. A device drawing 150 W runs at roughly 0.142 Btu/s.
Real-World Uses for This Conversion
Heating and Cooling Systems
Furnaces, air conditioners, and heat pumps often publish their heating or cooling capacity in Btu-based figures. Their electrical components, meanwhile, draw power measured in watts. Converting between the two lets you compare heat delivered against electricity consumed, which is essential for judging efficiency and estimating operating costs.
Water Heaters and Pool Heaters
Gas-fired water heaters and pool heaters are typically rated by their heat output in Btu terms. Electric models compete on wattage. Converting puts both options on equal footing so you can choose based on performance, not marketing labels.
Power Generation and Engines
Engines and generators burn fuel at a rate that engineers track in Btu per second. The electricity they produce shows up in watts or kilowatts. Comparing the two reveals how much usable power you get from the energy you feed in.
Data Centers and Large Facilities
Servers consume power in watts and give nearly all of it back as heat. Cooling systems designed to remove that heat may be specified in Btu-based terms. Accurate conversion keeps cooling capacity matched to the actual heat load, protecting equipment and controlling costs.
Btu/s to Watts Conversion Table
Use this quick-reference chart for common values. Each figure uses the standard relationship of 1 Btu/s ≈ 1,055.06 W.
| British Thermal Units Per Second (Btu/s) | Watts (W) | Kilowatts (kW) |
|---|---|---|
| 1 | 1,055.06 W | 1.06 kW |
| 2 | 2,110.11 W | 2.11 kW |
| 5 | 5,275.28 W | 5.28 kW |
| 10 | 10,550.56 W | 10.55 kW |
| 20 | 21,101.12 W | 21.10 kW |
| 50 | 52,752.79 W | 52.75 kW |
| 100 | 105,505.59 W | 105.51 kW |
| 500 | 527,527.93 W | 527.53 kW |
Common Mistakes to Avoid
- Treating Btu as power. A lone Btu is energy. Only with a time unit attached, such as per second, does it become power.
- Ignoring the time unit. Btu per second and Btu per hour are wildly different rates. Check the label twice before converting.
- Rounding too early. Carry extra decimal places through your calculations, then round only the final answer.
- Confusing input with output. Some equipment lists the energy it consumes and others list the heat it delivers. Know which number you're holding before you convert.
The Bottom Line
Btu per second and watts are two dialects of the same language: power. One belongs to the world of thermal engineering, the other to electrical standards everywhere. With the fixed relationship of 1 Btu/s ≈ 1,055.06 W, you can translate any rating in either direction and make genuinely informed comparisons.
Ready to convert a specific value? Use the converter above for instant, accurate results, and bookmark this page the next time a spec sheet mixes its units.