Core answer: 1 kW = 1,000 W; 1 horsepower (metric PS) = 735.5 W, 1 mechanical hp = 745.7 W — so a 150 PS car is ~110 kW. Electricity bills count ENERGY (kWh), not power: a 2 kW heater running 3 h uses 6 kWh. EV charging: 7 kW home pile adds ~40–50 km of range per hour; 120 kW fast charging adds ~600 km/h theoretical.
The conversion spine
| Unit | In watts | Seen on |
|---|---|---|
| 1 W | 1 | LED chips |
| 1 kW | 1,000 | appliances, EV chargers |
| 1 PS (metric hp) | 735.5 | Chinese/EU car specs |
| 1 hp (mechanical) | 745.7 | US/UK cars |
| 1 匹 (AC "horse") | ~735 W cooling input | but marketed as ~2,500 W cooling output |
| 1 MW | 10⁶ | power plants |
The air-conditioner 匹 trap
"1 匹" historically = 735 W of INPUT power, but modern efficiency (COP ≈ 3.5) turns that into ~2,500 W of cooling. Shopping by 匹:
| 匹数 | Cooling output | Room size |
|---|---|---|
| 1 匹 | ~2,500 W | 10–15 m² |
| 1.5 匹 | ~3,500 W | 15–22 m² |
| 2 匹 | ~5,000 W | 22–30 m² |
| 3 匹 | ~7,200 W | 30–45 m² |
Worked examples
Example 1 — Car power. 110 kW ÷ 0.7355 ≈ 150 PS; US spec sheet says 148 hp. The numbers differ by unit, not by engine.
Example 2 — Monthly bill. 1.5匹 AC (input ~1.1 kW) × 8 h/day × 30 days × 0.6 duty cycle ≈ 158 kWh ≈ ¥87/month.
Example 3 — EV charging math. A 60 kWh battery from 20% to 90% = 42 kWh needed: on 7 kW home charging ≈ 6 h (overnight ✓); on 120 kW DC ≈ 21 min (real-world taper makes it ~35 min).
Example 4 — Generator sizing. Fridge (150 W, but 3–5× startup surge) + 10 LED lights (100 W) + router (15 W): a 1 kW generator covers running load, but pick 2 kW for the surge.
Common mistakes and myths
- kW vs kWh — kW is the tap's flow, kWh is the bucket's fill; "my heater used 2 kW today" is meaningless without hours.
- PS vs hp — they differ by 1.4%; mixing them in spec comparisons is pedantic but real.
- Rated vs actual consumption — a 2,000 W heater on medium draws ~1,000 W; the nameplate is a ceiling, not a constant.
- "Higher horsepower = faster" — power-to-weight decides: 100 PS in a 1-tonne car beats 150 PS in a 2-tonne SUV off the line.
- Believing inverter AC marketing — "一晚一度电" (1 kWh/night) assumes ideal lab conditions; real bedrooms use 3–8 kWh.