How do you use the AC size calculator?
Use it in four steps: enter room area, pick ceiling height, choose sun exposure, then enter occupant count. The result appears within 25 seconds, showing both the BTU figure and the closest tonnage a Saudi retailer stocks.
- 0110 seconds
Enter room area
Multiply length by width in meters. The calculator accepts 6 to 200 square meters.
- 025 seconds
Pick ceiling height
2.7 meters is standard in Saudi apartments. A taller ceiling raises the cooled volume and the load.
- 035 seconds
Choose sun exposure
Pick direct for south- or west-facing walls and large windows, or low for interior rooms.
- 045 seconds
Enter occupant count
Each occupant beyond the first two adds sensible and latent heat the calculator accounts for automatically.
How is the required cooling capacity calculated?
The formula is (area × 600 BTU per sqm × ceiling factor × sun factor + occupancy load) × 1.1, rounded up to the nearest tonnage sold locally. A 20-sqm room with 2 occupants needs 13,200 BTU after correction, rounding to a 1.5-ton unit.
The base load starts at 600 BTU per square meter, calibrated for a hot design climate rather than the 500 BTU figure common in temperate-climate calculators. A 2.7-meter ceiling carries a factor of 1, a 3.2-meter ceiling carries 1.12, and a 3.8-meter ceiling carries 1.25.
Sun exposure adds a factor of 0.9 for low exposure, 1 for medium, and 1.15 for direct exposure through large windows or an unshaded west wall. Occupancy adds 600 BTU for every occupant beyond the first two, covering both the body heat and the moisture each additional person releases.
A worked example: a 25-sqm room, 3.2-meter ceiling, direct sun, 4 occupants. The base load is 25 × 600 × 1.12 × 1.15, which equals 19,320 BTU. Adding 1,200 BTU for the two extra occupants brings the subtotal to 20,520 BTU. The 1.1x Eastern Province factor then raises it to 22,572 BTU, rounding up to a 2-ton unit.
| Factor | Value | Reason |
|---|---|---|
| Base load per sqm | 600 BTU | Calibrated for a high design temperature, above the 500 BTU used in temperate climates |
| Ceiling factor, 2.7m | x1 | Standard Saudi apartment ceiling height |
| Ceiling factor, 3.2m | x1.12 | Larger cooled volume above the room |
| Ceiling factor, 3.8m | x1.25 | Villa majlis and double-height living rooms |
| Sun factor, low | x0.9 | Interior rooms with minimal direct exposure |
| Sun factor, medium | x1 | Standard exposure, the calculator default |
| Sun factor, direct | x1.15 | South- or west-facing walls, large glazing |
| Occupant load | 600 BTU each, beyond 2 | Sensible and latent heat per additional occupant |
| Eastern Province factor | x1.1 | Applied last, on the full subtotal |
What factors affect the sizing result?
Four inputs move the result: room area, ceiling height, sun exposure and occupant count, each in a different direction and magnitude. Area has the largest single effect, since every extra square meter adds 600 BTU before any multiplier is applied.
An undersized unit is the costlier mistake in practice. It runs continuously without ever reaching the set temperature, and the compressor short-cycles trying to catch up, which shortens its working life faster than correct sizing would.
| Factor | Direction | Magnitude |
|---|---|---|
| Room area | Linear increase | 600 BTU per additional square meter |
| Ceiling height | Step increase at 3.2m and 3.8m | Up to 25% more load at 3.8 meters |
| Sun exposure | Step increase for direct exposure | Up to 15% more load with direct sun |
| Occupant count | Step increase past 2 occupants | 600 BTU per person beyond the first two |
How does AC sizing change under Eastern Province conditions?
A room in the Eastern Province needs roughly 10% more cooling capacity than the same room in a temperate climate, because a 50°C design ambient cuts condenser efficiency and high humidity adds latent load the base formula does not capture on its own.
The 1.1x correction is applied once, at the end of the calculation. This keeps it separate from the base 600 BTU figure, so the tool can show each step on its own for a transparent result.
Filter and coil dust from Eastern Province storms is a separate effect from sizing. A clogged filter does not change the rated capacity a unit was built to deliver. It slows airflow enough that the compressor runs longer to reach the same set temperature. Three filter washes a year, matching the regional cleaning schedule, keeps runtime close to the sized figure.
What else helps you choose the right AC?
2 guides extend the sizing result into a full buying decision: a breakdown of AC types by how each one cools a room, and a brand comparison that states honest drawbacks instead of only listing features.
Frequently asked questions
How many tons of AC do I need for a 20 sqm room?
A 20-sqm room with 2 occupants, standard ceiling and medium sun needs about 13,200 BTU after the Eastern Province correction, which rounds up to a 1.5-ton unit.
Why does this calculator recommend a bigger unit than others?
It applies a 1.1x correction calibrated for a 50°C design ambient and Gulf humidity. Calculators built for temperate climates skip this step and undersize the unit for local summers.
What happens if I install an oversized AC unit?
An oversized unit reaches the set temperature quickly, then shuts off, so its cycles run too short to remove humidity. The room stays cool but damp, and frequent starts wear the compressor faster.
Does ceiling height really change the tonnage I need?
Yes, a 3.8-meter ceiling carries a 1.25x factor versus 1 for a standard 2.7-meter ceiling, because the calculator is sizing the cooled air volume above the room, not just the floor area.
Does more occupants change the result by much?
Each occupant beyond the first two adds 600 BTU. A room with 6 occupants instead of 2 adds 2,400 BTU, close to a fifth of a typical 1.5-ton unit's total capacity.