Convert between watts, kilowatts, horsepower, and BTU/h — with the watt-based steps shown.
A 2,000-watt hair dryer is 2.68 horsepower; a 12,000 BTU/h air conditioner is 3.52 kW — power wears many unit costumes, and converting by hand means the 745.7 W/hp factor that nobody carries in their head. Our free Power Converter translates watts, kilowatts, mechanical horsepower, BTU/h, and ft·lbf/s through the watt base, showing both steps plus a light-bulb benchmark that makes any wattage instantly feelable.
Power is the rate of energy flow — energy per unit time. The SI watt (W) is one joule per second. Horsepower (745.7 W, mechanical) is James Watt’s 18th-century marketing unit — roughly one draft horse’s sustained output — still ruling engines and motors. BTU/h dominates American HVAC. They’re all the same dimension; the converter speaks all the dialects.
Enter any power and get the converted value to four decimals plus the bulb count — because “3,517 W” clicks when you hear “fifty-nine light bulbs.” Engineers, shoppers comparing appliances, students, and the horsepower-curious get transparent steps and exact factors.
Power = energy ÷ time. The watt — 1 J/s — is coherent with SI: a 100 W bulb converts 100 joules of electrical energy into light and heat every second. Because it ties electricity (volts × amps = watts), mechanics (force × velocity = watts), and heat (joules/second = watts) together with no factors, the watt is the natural base the converter routes everything through.
Horsepower’s origin is pure marketing: James Watt needed to sell steam engines to mine owners who bought horses, so he measured a brewery horse’s work and defined 1 hp = 550 ft·lbf/s = 745.7 W. It was an estimate — real horses peak higher — but the number stuck, was standardized, and now rates every car engine on Earth. The converter uses the mechanical (imperial) horsepower, 745.69987 W.
BTU/h is power disguised as heating: 1 BTU/h = 0.29307107 W. American furnaces and AC units are sold by BTU/h (a “12,000 BTU” AC is really 12,000 BTU/hour), which is why the converter labels it explicitly — the “per hour” is load-bearing, and dropping it is the classic HVAC error.
Key terms:
The mechanical horsepower 745.69987158227022 W is rounded to 745.7 here (0.00004% difference — invisible on any nameplate). Metric horsepower (PS, 735.5 W) is a different unit; this converter uses mechanical hp.
A 2000 W hair dryer — how many horsepower is that?
Your hair dryer out-powers two horses — briefly. (Horses sustain ~1 hp; they peak near 15.) The bulb count (33) is the honest scale of it.
A 12,000 BTU/h window AC — what’s that in kW?
“One ton of cooling” = 12,000 BTU/h = 3.517 kW — the converter reproduces the HVAC industry’s defining equivalence exactly.
A homeowner’s well pump draws 1.5 hp; the generator must cover starting surge (~3× running). Converting: 1.5 × 745.7 = 1118.55 W running, × 3 = 3355.65 W surge — a 4 kW generator with margin. Buying the 3 kW unit (“close enough”) would stall on every startup. The hp-to-watts conversion, done exactly, sized a $600 purchase correctly.
The bulb benchmark quietly helped: 3,356 W ÷ 60 = 56 bulbs — picturing 56 bulbs flickering on at once makes “starting surge” visceral in a way watts don’t. Benchmarks sell understanding; steps sell accuracy; the widget gives both.
A second scenario: the EV comparison. A Tesla Model 3 motor peaks at 211 kW; grandpa’s Mustang made 300 hp: 300 × 745.7 ÷ 1000 = 223.71 kW — the old V8 edges the EV on peak power, though the EV’s instant torque wins the drag race. Power is only half the story — but it’s the half converters handle.
A third: the data center. A rack draws 8 kW; cooling must remove it as heat: 8 ÷ 0.29307107 = 27,297 BTU/h — about 2.3 tons of cooling per rack. Facility planners run this conversion per rack, hundreds of times — the widget’s exact factor beats the “3.4 kBTU per kW” rule of thumb when the chiller quote is on the line.
James Watt’s horse was measured at a brewery, pulling a mill wheel — and modern estimates say his “horse” was generous, maybe 1.5× a real sustained horse. It didn’t matter: the unit’s job was selling engines, and “20 horsepower” outsold “14,914 watts” (a unit that didn’t exist yet) effortlessly. The best unit often wins on rhetoric, not logic.
Standardization tamed it: 550 ft·lbf/s exactly, hence 745.69987158227022 W — the infinite decimal coming from 550 × 1.3558179483314004. Engineers round to 745.7 without guilt; the 0.00004% truncation is 0.3 W on a 700 kW engine — lost in the noise of a single degree of temperature.
The watt’s revenge is total in science and growing everywhere else: EVs are sold in kW globally, solar in watts, data centers in megawatts. Horsepower survives where romance lives — cars, boats, lawnmowers — the machines people feel. Units, like languages, persist through affection.
BTU/h’s empire is American buildings: every furnace, AC, and water heater wears it, and the “ton of refrigeration” (12,000 BTU/h — the cooling of melting a ton of ice daily) is its crown jewel. The unit is a fossil of the ice-harvesting era doing modern thermodynamic duty — history doesn’t repeat, but it air-conditions.
Human power calibrates the scale: ~100 W sustained (a fit cyclist), 400 W bursts, 2000 W for seconds (elite sprinters). A horsepower is 7–8 humans — which reframes every engine as a team of invisible laborers. The widget’s bulb benchmark does the same work visually: watts become workers, or bulbs, and abstraction becomes intuition.
The kW/kWh confusion costs grid planners real money: headlines about “gigawatt batteries” usually mean gigawatt-hours, and the missing “h” swaps instantaneous output for stored capacity — a billion-dollar syllable. The converter’s strict power-only scope is a design decision: units that must never mix get separate tools.
One more pattern: convert power for comparison, energy for billing. “Which heater is stronger?” is watts; “what will it cost?” is kilowatt-hours (watts × time × rate). The two questions need two converters — this one and the energy converter — and professionals reach for each without thinking. That reflex is the real skill; the tools just execute it.
Power converter: watts = value × from-factor; result = watts ÷ to-factor. Factors (W): hp(mech)=745.7, kW=1000, BTU/h=0.29307107, ft-lbf/s=1.35581795, W=1. Bonus: 60-W bulb count. Power-only (not energy). Source: Sigma Calculator, Power Converter, https://sigmacalculator.net/math-calculators/power-converter/
Cite this page as: Power Converter, Sigma Calculator, https://sigmacalculator.net/math-calculators/power-converter/
Last updated: October 12, 2026