Power Converter: Watts, HP, kW & BTU/h Explained Simply
What a Power Converter Actually Does
A power converter translates one unit of power into another. That's it. You put in a number, pick the unit you have, pick the unit you want, and it gives you the equivalent. The reason this matters is that power shows up in a dozen different units depending on who's talking. An electrician talks in watts and kilowatts. A mechanic talks in horsepower. An HVAC tech talks in BTU per hour. A physics textbook might throw ergs per second at you. Without a converter, you're stuck doing decimal gymnastics on a napkin.
The Unit Converter Pro power converter handles the common ones — watt, kilowatt, megawatt, horsepower (mechanical and metric), BTU/h, foot-pound per second, and a few others — without making you remember that 1 hp equals 745.7 W or that 1 BTU/h is roughly 0.293 W. You just type and read.
Why You'd Need One (Beyond Homework)
If you're sizing a generator for a job site, you've got equipment rated in horsepower and a generator rated in kilowatts. Those two numbers don't talk to each other until you convert. Guess wrong and you buy a generator that trips its breaker the first time the compressor kicks on.
Same story with air conditioners. A window unit might say 5,000 BTU/h on the box, but the spec sheet for the circuit says you've got 1,500 watts available. Are you fine? Convert 5,000 BTU/h to watts and you get about 1,465 W — close enough that you'd want to check the startup draw. That's a real decision, not a classroom exercise.
Car people run into this constantly. Engine output is in horsepower, but electric motor swaps are rated in kilowatts. A 150 kW motor is about 201 hp. If you're comparing a gas engine to an EV conversion, you need that conversion or you're comparing apples to alternators.
The Units You'll Actually See
Most power conversions fall into five families:
- Watt (W) — the SI unit. Everything else is defined against it.
- Kilowatt (kW) — 1,000 watts. Utility bills, generators, motors.
- Megawatt (MW) — 1,000,000 watts. Power plants, data centers.
- Horsepower (hp) — 745.7 W for mechanical/imperial hp; 735.5 W for metric hp. They're close but not identical, and the difference matters at high values.
- BTU per hour (BTU/h) — 0.293071 W. Heating and cooling equipment in the US.
There's also the foot-pound per second (1 ft·lb/s = 1.35582 W) and the less common erg per second (1 erg/s = 0.0000001 W), which you'll only see in older scientific papers.
A good converter shows you these side by side so you can sanity-check. If you convert 10 hp and get 7,457 W, that's right. If you get 7.5 W, something's off — and you'd catch it by looking at the magnitude.
How to Convert Without Losing Your Mind
The manual method is simple multiplication, but the numbers are ugly. To go from horsepower to watts, multiply by 745.7. To go from watts to BTU/h, multiply by 3.412. To go from kilowatts to horsepower, multiply by 1.341.
The problem isn't the math — it's remembering which factor goes which way. Do you multiply or divide? That's where people mess up. A converter removes that step. You select "from" and "to" and it does the direction for you.
Here's a quick reference for the most common conversions:
- 1 hp = 745.7 W = 0.7457 kW
- 1 kW = 1.341 hp = 3,412 BTU/h
- 1 BTU/h = 0.293 W
- 1 ton of refrigeration = 12,000 BTU/h = 3.517 kW
- 1 MW = 1,000 kW = 1,341 hp
If you're doing this more than once a month, bookmark a converter. It's faster than pulling up a search result and squinting at a table.
Common Mistakes (and How to Avoid Them)
Mixing up hp and metric hp. Mechanical horsepower is 745.7 W. Metric horsepower (PS) is 735.5 W. That's a 1.4% difference. On a 500 hp engine, that's 7 hp — enough to matter if you're comparing specs across regions.
Forgetting that BTU/h is a rate, not a quantity. BTU is energy. BTU/h is power. If a heater says 10,000 BTU, that's the total heat it can deliver over some time — usually per hour, but not always stated. Check the unit.
Assuming all watts are the same. Real power (watts) vs. apparent power (volt-amperes) vs. reactive power (VAR) are different things. A power converter handles real power. If you're working with AC circuits and power factor, you need a different calculation.
Rounding too early. Convert 1 hp to kW: 0.7457. If you round to 0.75 and then multiply by 100, you get 75 kW instead of 74.57 kW. Small, but it compounds.
A Practical Takeaway
Before you buy any equipment that lists power in a unit you don't use daily, convert it to the unit on your breaker panel or your utility bill. That's almost always watts or kilowatts. It takes ten seconds and prevents the scenario where you've got a 3 kW load on a 2.4 kW circuit.
If you're comparing two products — say a 5 hp pump and a 3.7 kW pump — convert both to the same unit. They're actually the same power (5 hp ≈ 3.73 kW), which you'd only know after converting. Spec sheets love to use different units to make products look better or worse than they are.
Frequently Asked Questions
Q1: How many watts are in one horsepower?
One mechanical horsepower equals 745.7 watts. Metric horsepower equals 735.5 watts. The difference is small but real, so check which one your source is using.
Q2: Can I convert kilowatts to BTU per hour directly?
Yes. Multiply kilowatts by 3,412 to get BTU/h. For example, 3 kW is 10,236 BTU/h. A power converter does this instantly without you needing to remember the factor.
Q3: Why does my generator's power rating not match my equipment's?
Generators are often rated in kilowatts or kVA, while motors and tools are rated in horsepower. You have to convert one to the other to compare. Also check whether the generator rating is continuous or peak — peak ratings only hold for a few seconds.
Try the free tool — it takes seconds.
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