11 units — watts, three horsepower types, BTU/h & thermal units
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3 hp types, watts, thermal — all at once
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| Unit | Symbol | Category | 1 Unit = (in watts) |
|---|---|---|---|
| Watt | W | Metric (SI base) | 1 |
| Kilowatt | kW | Metric (SI) | 1,000 |
| Megawatt | MW | Metric (SI) | 1,000,000 |
| Gigawatt | GW | Metric (SI) | 1,000,000,000 |
| Mechanical Horsepower | hp / bhp | Horsepower (US/UK) | 745.7 |
| Metric Horsepower | PS / CV / ch | Horsepower (EU/JP) | 735.5 |
| Electrical Horsepower | hp (E) | Horsepower (Motors) | 746 |
| BTU per Hour | BTU/h | Thermal (US) | 0.293071 |
| Ton of Refrigeration | TR | Thermal (HVAC) | 3,516.85 |
| Foot-Pound per Second | ft·lb/s | Mechanical | 1.35582 |
| Calorie per Second | cal/s | Thermal | 4.1868 |
Mechanical horsepower (745.7 W) is James Watt's original definition from the 1780s. Watt observed that a mine pony could lift 220 pounds of coal 100 feet per minute, extrapolated to a horse (1.5× stronger), and rounded up for marketing margin — arriving at 33,000 ft·lb/min = 550 ft·lb/s = 745.7 watts. Metric horsepower / PS / CV (735.5 W) was defined in 19th-century Germany as 75 kilogram-force meters per second (75 kgf·m/s) — a nice round metric number that inadvertently undershoots Watt's value by 1.4%. Electrical horsepower (746 W) is the IEEE/ANSI standard — exactly 746 watts, chosen as a clean approximation of mechanical hp for motor nameplate ratings.
The practical impact: a European car advertised as "200 PS" is actually 197 mechanical hp (147 kW). A US car rated "200 hp" is 203 PS (149 kW). The 1.4% difference sounds trivial, but across a product lineup, marketing departments care deeply about which number appears in the brochure. This converter shows all three simultaneously so you can see the difference at any value.
1 BTU (British Thermal Unit) is the energy needed to raise 1 pound of water by 1°F. BTU/h (BTU per hour) is the standard power unit for heating and cooling equipment in the United States. 1 ton of refrigeration = 12,000 BTU/h = 3.517 kW — this is the amount of continuous heat removal needed to freeze one short ton (2,000 lbs) of water at 32°F into ice at 32°F in 24 hours. The term is literally 19th-century ice-industry jargon: before electric refrigeration, buildings were cooled with harvested ice blocks measured in tons. A window AC unit is typically 0.5-1.5 tons. A central AC for a 2,000 sq ft home is 2-5 tons (24,000-60,000 BTU/h). A large office building may have 100-500+ tons of cooling capacity. The industry never abandoned the ice-age terminology.
| From | To | Multiply By | Example |
|---|---|---|---|
| Mechanical hp | Kilowatts | × 0.7457 | 200 hp = 149.1 kW |
| Metric hp (PS) | Kilowatts | × 0.7355 | 200 PS = 147.1 kW |
| Kilowatts | Mechanical hp | × 1.34102 | 100 kW = 134.1 hp |
| Mechanical hp | Metric hp (PS) | × 1.01387 | 200 hp = 202.8 PS |
| BTU/h | Watts | × 0.293071 | 12,000 BTU/h = 3,517 W |
| Ton of Refrig. | BTU/h | × 12,000 | 3 tons = 36,000 BTU/h |
| Ton of Refrig. | Kilowatts | × 3.51685 | 5 tons = 17.6 kW |
| Watts | BTU/h | × 3.41214 | 1,000 W = 3,412 BTU/h |
| Electrical hp | Watts | × 746 | 1 hp (E) = 746 W |
| ft·lb/s | Watts | × 1.35582 | 550 ft·lb/s = 745.7 W |
Enter your value in the Mechanical Horsepower (hp) field. 1 hp = 0.7457 kW. For metric hp (PS), use the Metric Horsepower field — 1 PS = 0.7355 kW. Example: 200 mechanical hp = 149.1 kW; 200 PS = 147.1 kW.
Mechanical hp = 745.7 W (James Watt's original, US/UK cars). Metric hp/PS = 735.5 W (European/Japanese cars). Electrical hp = 746 W (electric motor ratings). A car rated 200 hp (US) = 203 PS (EU) = 149.1 kW. The ~1.4% mechanical vs. metric difference matters when comparing specs internationally.
Enter your BTU/h value. 1 BTU/h = 0.293 W. 1 kW = 3,412 BTU/h. For AC sizing: 12,000 BTU/h = 3.517 kW = 1 ton. Quick estimate: divide BTU/h by 3,400 to get approximate kW.
1 ton = 12,000 BTU/h = 3.517 kW — the cooling needed to freeze one ton of ice in 24 hours. The term predates electric refrigeration: 19th-century buildings were cooled with harvested ice blocks. Today it's the standard AC rating: home units are 1-5 tons, commercial buildings 50-500+ tons.
1 GW = 1,000 MW = 1 billion watts. A nuclear reactor produces ~1 GW. Hoover Dam: ~2 GW. Large wind turbine: ~3-8 MW. A typical home uses ~1.2 kW average. So 1 GW powers roughly 800,000 homes. The DeLorean in Back to the Future needed 1.21 GW — roughly the entire output of Iran's Bushehr nuclear plant.