Power Unit Converter

Power is energy per unit time (W = J/s) and shows up everywhere from light bulbs (watts) to engines (hp / PS / kW) and air-conditioners (BTU/hr, refrigeration tons). Enter a value in any unit and instantly see all 10 common power units side-by-side — W, kW, MW, hp (mechanical), PS (metric), BTU/hr, ft·lbf/s, cal/s, kcal/h and RT (refrigeration ton).

From

Live value in every power unit

W Watt —

kW Kilowatt —

MW Megawatt —

hp Mechanical horsepower (imperial hp) —

PS Metric horsepower (PS / cv) —

BTU/hr BTU per hour —

ft·lbf/s Foot-pound-force per second —

cal/s Calorie per second —

kcal/h Kilocalorie per hour —

RT Refrigeration ton (USRT) —

Heads-up: 1 hp ≈ 0.7457 kW; 1 PS ≈ 0.7355 kW; 1 RT = 12 000 BTU/h ≈ 3.517 kW. HK aircons quote BTU/h for cooling capacity; engines use PS (EU/JP) or hp (US).

W Appliances, light bulbs, audio speaker ratings
kW EV motor output, industrial machinery
hp US-market vehicles, engine and machinery ratings
PS EU/JP vehicle specs (PS, cv)
BTU/hr AC and heater ratings — the HK standard
RT Commercial AC, chillers, HVAC specifications

—

Formula

Every unit is converted into watts (W) and then divided by the target unit’s watt-equivalent.

· 1 W = 1 J/s (SI base); 1 kW = 1 000 W and 1 MW = 10⁶ W (exact).
· 1 hp (mechanical / imperial) = 550 ft·lbf/s ≈ 745.6999 W (NIST SP 811).
· 1 PS (metric horsepower / cv) = 75 kgf·m/s = 735.49875 W exactly.
· 1 BTU/hr ≈ 0.293 071 W (ISO 31-4 International Table BTU; 1 BTU_IT = 1 055.05585262 J).
· 1 cal/s = 4.184 W exactly (thermochemical calorie); 1 kcal/h = 4 184 ÷ 3 600 ≈ 1.1622 W.
· 1 refrigeration ton (USRT) = 12 000 BTU/hr ≈ 3 516.85 W (ASHRAE: the cooling needed to melt 1 short ton of ice in 24 h).
· HK aircon labels rate cooling capacity in BTU/hr; "1 匹" is colloquial and roughly maps to a 9 000–10 000 BTU/hr unit (~750 W electrical input).
· Vehicle horsepower: EU/JP brochures usually quote PS (a.k.a. cv); US brochures quote imperial hp. 1 hp ≈ 1.0139 PS — they differ by ≈ 1.4 %.
· Sources: NIST SP 811 App. B (2008 ed.), BIPM SI Brochure 9th ed., ISO 31-4 / 80000-5, ASHRAE Handbook (HVAC chapter).

Frequently asked

A BMW M3 brochure says 480 hp — what is that in PS and kW?

480 hp (mechanical) ≈ 486.7 PS ≈ 357.9 kW. EU/JP brochures list PS (metric horsepower, also called "cv" or just "horsepower"), US brochures list imperial hp — they differ by ≈ 1.4 % (1 hp = 1.0139 PS). This tool flips between them in one click.

An HK aircon is labelled 12 000 BTU — how many "horse" is that and how many kW?

12 000 BTU/hr of cooling capacity ≈ 3 517 W ≈ 3.517 kW — exactly one refrigeration ton (1 USRT, the formal unit). Colloquially HK retailers call this "1.5 匹" but "匹" is not a standardised unit — EMSD energy-efficiency labels, manufacturer spec sheets and HK building codes all use BTU/hr or W/kW. Electrical input (what shows up on your bill) is the cooling capacity divided by EER/COP (typically 2.5–3.5), so a 12 000 BTU unit draws ≈ 1 000–1 400 W.

Why are 1 hp and 1 PS different if both mean "one horsepower"?

Both terms were coined in the 19th century to describe steam-engine output but their definitions differ. James Watt used the imperial system: 1 hp = 550 ft·lbf/s ≈ 745.7 W. Europe — especially Germany — later defined a metric version: 1 PS (Pferdestärke) = 75 kgf·m/s = 735.49875 W. The gap comes purely from the foot-pound-force vs metre-kilogram-force units. Today most car-makers (including Japanese ones quoting "馬力") publish PS; North America stays on imperial hp, so spec sheets for the same engine differ by ≈ 1.4 %.

My electric water heater is rated 3 kW — what is that in BTU/hr?

3 kW ≈ 10 236 BTU/hr. 1 W = 3.412 BTU/hr (International Table BTU), so 3 000 W × 3.412 ≈ 10 236 BTU/hr. Your water heater can dump ≈ 10 236 BTU of heat per hour into the tank — note this is heat output, not the same direction as the cooling load of a 10 000 BTU/hr aircon, even though the numbers happen to be similar.

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