Enter your room size, BTU rating, or horsepower value to size an air conditioner or convert between AC HP, BTU/hr, and watts.
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Formula
Room size → HP:
HP = (A × C + O) ÷ 9,000
where A = room area (m²), C = climate load factor (BTU/m²), O = occupancy load (BTU)
BTU → HP:
HP = BTU/hr ÷ 9,000
where 1 AC HP ≈ 9,000 BTU/hr of cooling
HP → power:
Watts = BTU/hr × 0.293 (AC HP rating)
Watts = HP × 745.7 (mechanical HP)
Interpretation
The result tells you the cooling capacity needed, not the electrical power drawn. AC horsepower is a cooling-output rating used mostly in Asia and the Philippines, where 1 HP roughly equals 9,000 BTU/hr or 2.64 kW of cooling. Match the calculated HP to the nearest standard size by rounding up — undersized units run constantly and fail to cool, while oversized units short-cycle and leave humidity high.
- 0.5 HP — small bedroom, ~5–7 m² (54–75 sq ft)
- 0.75 HP — bedroom, ~8–11 m² (86–118 sq ft)
- 1.0 HP — standard bedroom, ~12–15 m² (129–161 sq ft)
- 1.5 HP — large bedroom or small living room, ~16–22 m² (172–237 sq ft)
- 2.0 HP — living room, ~23–30 m² (247–323 sq ft)
- 2.5–3.0 HP — large open space, 30+ m²
Quick Reference Table
| AC HP | BTU/hr | kW (cooling) | Watts | Typical room (tropical) |
|---|---|---|---|---|
| 0.5 | 4,500 | 1.32 | 1,319 | ~7 m² / 75 sq ft |
| 0.75 | 6,750 | 1.98 | 1,978 | ~11 m² / 118 sq ft |
| 1.0 | 9,000 | 2.64 | 2,637 | ~15 m² / 161 sq ft |
| 1.5 | 13,500 | 3.96 | 3,956 | ~22 m² / 237 sq ft |
| 2.0 | 18,000 | 5.27 | 5,274 | ~30 m² / 323 sq ft |
| 2.5 | 22,500 | 6.59 | 6,593 | ~37 m² / 398 sq ft |
| 3.0 | 27,000 | 7.91 | 7,911 | ~45 m² / 484 sq ft |
FAQ
Is AC horsepower the same as mechanical horsepower?
No. AC HP rates cooling output (1 HP ≈ 9,000 BTU/hr), while mechanical HP rates motor shaft power (1 HP ≈ 745.7 W). An air conditioner's electrical input is usually much lower than its cooling output because the refrigeration cycle moves heat rather than generating it.
How much electricity does a 1 HP aircon use?
A 1 HP inverter unit typically draws 700–900 W at steady state, even though it delivers about 2,640 W of cooling. Non-inverter models may draw 900–1,100 W. Check the unit's EER or input wattage on the nameplate rather than assuming from HP alone.
What if my room gets direct sunlight or has high ceilings?
Use the "hot + sun-exposed" climate option, or bump up one HP size. Add roughly 10% more capacity for every meter of ceiling height above 2.7 m, and extra for west-facing windows, kitchens, or rooms with many appliances.
Should I round up or down to a standard size?
Always round up to the next available size for cooling. An undersized AC runs continuously without reaching the setpoint, while a slightly oversized unit only runs a bit longer per cycle — the exception is that heavily oversized units cool too fast to remove humidity.
