Power Units Explained: W, kW, hp, BTU/h
Convert between watts, kilowatts, horsepower, BTU per hour, and other power units with confidence.
What is power and why are there so many units?
Power is the rate at which energy is used or transferred. Every appliance, vehicle, and engine has a power rating, but units vary wildly across regions and industries. Electric appliances use watts, motors are rated in horsepower, and physicists work in joules per second. Heating and cooling systems use BTU per hour, while data centers often talk about kilowatts or even megawatts.
Understanding these units — and converting between them accurately — matters whether you are sizing a generator, comparing cars, or estimating electricity costs.
Common use cases
- Appliance ratings: Bulbs, microwaves, and vacuum cleaners in watts; air conditioners in BTU/h
- Cars and engines: Horsepower (hp) for cars, brake horsepower (bhp) for engines, kilowatts (kW) for EVs
- Solar and batteries: Solar panel output in watts or kilowatts, capacity in Wh or kWh
- Heating and cooling: BTU per hour for HVAC, watts for electric heaters
- Data centers and industry: Megawatts (MW) for large facilities, gigawatts (GW) for power plants
Method 1: Use UtilBoxx's free power converter (Recommended)
Our power unit converter supports watts, kilowatts, megawatts, gigawatts, milliwatts, horsepower (mechanical, metric, electric), BTU/h, foot-pounds per second, and more. Here is how to use it:
- Go to utilboxx.com/en/tools/unit/power
- Type a value in any field
- All other units update as you type
- Use the swap button to invert the conversion
- Copy any value with one click
Why this method works:
- 10+ power units in a single view
- Handles mechanical, metric, and electric horsepower correctly
- Exact constants, no rounding errors
- Mobile-friendly with large fields
- 100% in-browser, no server calls
Method 2: Memorize the key factors
A few anchor values cover most everyday conversions:
- 1 hp (mechanical) = 745.7 W = 0.7457 kW
- 1 hp (metric) = 735.5 W
- 1 BTU/h ≈ 0.293 W
- 1 kW = 1,000 W = 1.341 hp
- 1 MW = 1,000 kW = 1,000,000 W
For air conditioners, a common rule of thumb is 20 BTU/h per square foot of living space.
Method 3: Use a spreadsheet
In Excel or Google Sheets, you can build a quick conversion table:
``` = A1 745.7 // hp to W = A1 0.7457 // hp to kW = A1 * 3.41214 // W to BTU/h = A1 / 1000 // W to kW ```
This is convenient for engineering calculations or batch conversions.
Frequently asked questions
What is the SI unit of power?
The watt (W), defined as one joule per second. It is named after James Watt, the inventor who improved the steam engine. The kilowatt (kW) and megawatt (MW) are used for larger values.
What is the difference between horsepower and watts?
Horsepower is an older unit, originally defined to compare steam engines to draft horses. 1 mechanical hp = 745.7 W. Watts are the universal SI unit and are used in all scientific and most modern engineering contexts.
Why are there different types of horsepower?
Mechanical (imperial) horsepower, metric horsepower, and electric horsepower differ slightly. Mechanical hp = 745.7 W, metric hp = 735.5 W, electric hp = 746 W exactly. Car and engine specifications sometimes quote different versions.
How do I convert BTU/h to watts?
Multiply BTU/h by 0.293071. For example, 12,000 BTU/h ≈ 3,517 W ≈ 3.5 kW. The UtilBoxx power converter does this automatically.
Conclusion
Power ratings are everywhere — on appliances, vehicles, and HVAC systems. For a fast, accurate conversion, the UtilBoxx power converter is the easiest tool to keep on hand.