To size an AC for Pakistan, start from room area ÷ 130 to get tons, then increase it for tall ceilings, strong sun, a top-floor location and extra people. The adjusted figure is rounded up to the next practical AC size — 0.8, 1.0, 1.5 or 2.0 ton. A normal 12 × 12 ft bedroom lands around a 1.0–1.5 ton unit, settling at 1.5 ton when it is sunny or under the roof.
Key takeaways
- Base tons = area (ft²) ÷ 130. Sized for hot Pakistani summers.
- Add ~15% each for strong sun and for a top-floor room.
- Tall ceilings raise the load, and each occupant beyond two adds about 0.1 ton.
- Round up, not down in peak Pakistani summers.
- Standard sizes: 0.8, 1.0, 1.5, 2.0 ton.
How AC tonnage is estimated
One "ton" of cooling is the rate needed to melt a ton of ice in a day — about 12,000 BTU/hr. For Pakistan's hot summers we treat about 130 sq ft per ton as the base, then layer on multipliers for the things that add heat — a higher ceiling, strong sun and a top-floor ceiling exposed to the roof — and finally add a fixed amount for each extra occupant.
Here the height factor scales by ceiling height ÷ 10 ft, strong sun adds 15% and a top-floor room adds 15%; these combine into the adjustment multiplier shown in the result. Each occupant beyond two then adds about 0.1 ton on top. The result is rounded up to the next standard AC size so the unit is never undersized.
Worked example: a sunny 12 × 12 top-floor bedroom
Area = 12 × 12 = 144 sq ft. Base = 144 ÷ 130 = 1.11 ton. With a normal 10 ft ceiling (factor 1.0), strong sun (×1.15) and top floor (×1.15), the adjustment is about 1.32, giving an adjusted base of 1.11 × 1.32 ≈ 1.46 ton. With 2 occupants there is no extra people load, so the cooling load is about 1.46 ton, which rounds up to a 1.5 ton AC — the right size for this room in a hot Pakistani summer.
Quick room-size guide
| Room area | Typical AC size | Notes |
|---|---|---|
| Up to 110 ft² | 0.8 ton | Small bedroom |
| 110 – 130 ft² | 1.0 ton | Standard small room |
| 130 – 195 ft² | 1.5 ton | Standard / large bedroom |
| 195 – 260 ft² | 2.0 ton | Large room / living |
Based on ≈130 ft²/ton; step up a size for top-floor rooms, heavy sun, or extra occupants.
Planning the rest of the home
Sizing the slab above the room? Use the RCC slab calculator. Need a water tank for the household? Try the water tank calculator.
Frequently asked questions
How do I calculate AC tonnage for a room?
Area (ft²) ÷ 130 gives base tons for Pakistan's hot summers, then adjust up for height, sun, top floor and people and round to a standard size. A 150 ft² room generally needs a 1.5 ton AC.
What size AC do I need for a 12x12 room?
144 ft² gives about 1.11 ton base (144 ÷ 130), rising to roughly 1.46 ton with sun and a top floor. A 1.5 ton AC is the right size for a 12 × 12 room.
Is 1 ton AC enough for a 150 sq ft room?
Usually not for Pakistan — 150 ft² works out to about 1.15 ton base, so a 1.5 ton AC is the recommended size, more again for strong sun, a top-floor ceiling or extra people.
Does a top-floor room need a bigger AC?
Usually — the roof adds heat. This tool adds about 15% for a top-floor room, which can push you to the next size.
How does sun exposure affect AC size?
West/south rooms with big windows gain afternoon heat, so the tool adds about 15% for strong sun.
Why is AC sizing higher in hot climates?
Moderate-climate rules like 600 ft²/ton badly undersize AC for Pakistan. This tool uses about 130 ft²/ton to suit hot Pakistani summers and rounds up.
The area-per-ton method and ~12,000 BTU/hr per ton of refrigeration are standard HVAC rules of thumb; the ~130 ft²/ton base is calibrated for Pakistan's hot summers. Adjustment factors for ceiling height, occupancy, solar gain and roof exposure reflect common cooling-load practice; a precise figure requires a heat-load (Manual J) calculation for the specific room.
Last reviewed 2026-06-14