To find the right AC size, multiply the room’s floor area in square metres by 800 BTU if it’s uninsulated, or 600 BTU if it’s insulated. That’s the rule of thumb published by the Saudi Electricity Company (SEC). Then choose the next standard size up: a 4 × 5 m room (20 m²) without insulation needs 16,000 BTU, so an 18,000 BTU split fits.
Size is only half the decision; the other half is efficiency and professional AC installation, and this guide covers both.
BTU, tons and ‘units’ explained
- BTU (British Thermal Unit) measures how much heat an AC removes per hour. The higher the number, the more cooling.
- ‘Units’ (wahda): Saudi shops quote capacity in units of 1,000 BTU, so an ‘18-unit’ AC is 18,000 BTU.
- Tons: one ton is 12,000 BTU, so 18,000 BTU is 1.5 tons, 24,000 is 2 tons and 30,000 is 2.5 tons.
How to calculate the right AC size for a room
- Multiply the room’s length by its width in metres. Example: 4 × 6 = 24 m².
- Decide whether it’s insulated (thermal insulation in the walls and roof). If unsure, treat it as uninsulated.
- Multiply the area by 800 (uninsulated) or 600 (insulated). Example: 24 × 800 = 19,200 BTU.
- Pick the first standard size above the result: 12,000, 18,000, 24,000 or 30,000 BTU. Example: 24,000 BTU.
Split AC size chart by room area
| Room area | Uninsulated load (BTU) | Uninsulated AC (BTU) | Insulated load (BTU) | Insulated AC (BTU) |
|---|---|---|---|---|
| 9 m² (3 × 3) | 7,200 | 12,000 | 5,400 | 12,000 |
| 12 m² (3 × 4) | 9,600 | 12,000 | 7,200 | 12,000 |
| 16 m² (4 × 4) | 12,800 | 18,000 | 9,600 | 12,000 |
| 20 m² (4 × 5) | 16,000 | 18,000 | 12,000 | 12,000 |
| 24 m² (4 × 6) | 19,200 | 24,000 | 14,400 | 18,000 |
| 30 m² (5 × 6) | 24,000 | 24,000 | 18,000 | 18,000 |
| 36 m² (6 × 6) | 28,800 | 30,000 | 21,600 | 24,000 |
| 40 m² (5 × 8) | 32,000 | Two units (18,000 + 18,000) | 24,000 | 24,000 |
| 48 m² (6 × 8) | 38,400 | Two units (18,000 + 24,000) | 28,800 | 30,000 |
Notes on the chart:
- Below 12,000 BTU, choose 12,000, or a smaller model if your preferred brand offers one.
- When the load exactly matches a size (20 m² insulated = 12,000 BTU, for example), the AC will run flat out on the hottest days. If any factor below applies, go one size up.
- Above 30,000 BTU, split the load between two units at opposite ends of the space, or ask a technician about a larger floor-standing unit.
Factors that increase the cooling load
The 800/600 rule is a general estimate. A room needs more if it has:
- West-facing walls that take the afternoon sun, the hottest part of the day.
- A top-floor position under the roof, especially an uninsulated one.
- Large windows or glass walls, particularly without insulating curtains.
- Kitchen heat or other heat-producing appliances.
- Lots of people: a majlis that often hosts guests needs more than a bedroom of the same size.
- Eastern Province heat: long, hot summers in Dammam, Qatif and Saihat push ACs close to their limit at midday.
If an insulated room has one or two of these, use the uninsulated column. If several combine, such as a top-floor, west-facing room with big windows, have a technician estimate the load rather than jumping several sizes.
Undersized vs oversized: what goes wrong?
An undersized AC runs non-stop and still can’t reach the set temperature on a summer afternoon. It’s a well-known cause of ‘my AC isn’t cooling’, with higher consumption and constant strain on the compressor. Before blaming your current unit’s size, rule out the other causes in our guide to why an AC stops cooling, such as a dirty filter or low refrigerant.
An oversized AC cools quickly, then switches off before removing enough moisture, leaving the room cold but clammy, which is especially unpleasant in coastal homes. It also cycles on and off more often and costs more to buy, for no benefit. The right size beats ‘one size bigger, just in case’.
Torn between two sizes? Send Ali at Mousa Workshop the room’s dimensions, which way its windows face and a photo of the planned outdoor unit spot on WhatsApp, or call +966 54 372 8453 before you buy.
The SASO energy label: what A to G means
ACs in Saudi Arabia carry an energy label under SASO 2663:2021, graded A to G by SEER (seasonal energy efficiency ratio, in Btu/W·h). Notably, the Saudi calculation uses local weather data up to 46°C.
| Class | SEER (Btu/W·h) |
|---|---|
| A | 18.0 or higher |
| B | 15 to under 18 |
| C | 12.5 to under 15 |
| D | 10 to under 12.5 |
| E | 9 to under 10 |
| F | 8 to under 9 |
| G | Below 8 |
A higher SEER means less electricity for the same cooling, which matters because SEC says ACs account for more than 60% of household electricity. The updated SASO 2663:2025 takes effect on 1 December 2026, with SEER as the minimum efficiency requirement. For more savings, see how to cut your electricity bill while running the AC.
Inverter or fixed-speed?
- Fixed-speed: the compressor runs at full power or stops, so the temperature swings between cycles.
- Inverter: the compressor varies its speed to match the room, keeping the temperature steadier and usually using less power over long running hours. It costs more, and board repairs need an experienced technician.
The benefit is greatest in bedrooms and majlis rooms where the AC runs many hours a day. Either way, compare the SEER on the label rather than relying on the word ‘inverter’.
R-410A or R-32 refrigerant?
The refrigerant type is printed on the rating label. R-410A is still the most common in new units sold in Saudi Arabia, while R-32 is appearing on some models.
| Feature | R-410A | R-32 |
|---|---|---|
| Global warming potential (GWP) | 2,088 | 675 |
| Composition | Blend of two refrigerants | Single-component |
| Safety class | A1 (non-flammable) | A2L (mildly flammable) |
Every AC must be charged only with the refrigerant on its label, and gases must never be mixed. Daikin’s installation manual warns that air or foreign matter in the circuit causes an abnormal rise in pressure, so make sure your installer has the right tools for your AC’s refrigerant.
How to choose the best split AC for your home
There’s no single ‘best’ AC, whether you’re comparing 18,000 or 24,000 BTU models. The best one for you has:
- The right size for the room, from the chart and factors above.
- A high efficiency class, and the highest SEER among models of similar capacity.
- After-sales service, with spare parts and technicians in your area.
- A clear warranty: check what it covers and for how long, especially the compressor.
- Correct installation: a level indoor unit, a drain pipe with the right fall, pipes evacuated of air and moisture (vacuum) before start-up, and an outdoor unit in a shaded, well-ventilated spot.
Poor installation wastes the benefits of even the most expensive AC. Our AC service and installation price guide shows typical market prices.
When to call a technician
- The space is 40 m² or more.
- Several heat factors apply to the same room.
- You’re replacing an old AC because it ‘doesn’t cool’: the fault may be repairable, and a diagnosis settles that first.
- The outdoor unit will go in a tight or high spot.
- You’re moving an AC to another room: it needs proper removal, reinstallation and pipe evacuation.
Mousa Workshop provides AC installation and relocation and AC repair in Saihat and Anak, Qatif, Tarout, Dammam, Khobar, Safwa and Ras Tanura. Contact Ali any day from 8 am to 11 pm on WhatsApp or +966 54 372 8453; he’ll tell you the cost before starting.
Sources
Frequently asked questions
How many square metres does an 18,000 or 24,000 BTU AC cover?
Using SEC's rule, an 18,000 BTU unit covers about 22.5 m² in an uninsulated room or 30 m² in an insulated one. A 24,000 BTU unit covers about 30 m² uninsulated or 40 m² insulated, before allowing for extra heat factors.
Can one split AC cool an open-plan living area?
Usually not well, because a split AC blows air from a single point, so cooling doesn't reach rooms that are far away or closed off. Size each space separately, or ask a technician about spreading the load over more than one unit.
Can the outdoor unit go in a light well?
The Saudi Energy Efficiency Center advises against installing ACs in light wells and narrow spaces. The outdoor unit needs free-flowing air to reject heat, and a cramped spot makes it run hotter and use more power.
Does a high ceiling change the calculation?
Yes. The rule only uses floor area, so if the ceiling is clearly higher than normal, as in some majlis rooms and halls, there's more air to cool and you'll need more capacity. Ask a technician to estimate the load.