What size air conditioner do you need? (kW & BTU guide)
How to match AC size to your room in square meters, what kW and BTU actually mean, and why an oversized unit is a mistake — with the typical sizes sold in North Macedonia.
By ORVIA Editorial Team · Published July 6, 2026 · 5 min read
Room size is the one spec you cannot get wrong when buying an air conditioner. A unit that is too small runs flat out all summer and never quite cools the room; one that is too big costs more than it should have and cools badly in a different way. This guide maps square meters to the kW and BTU classes actually sold in North Macedonia, and shows what to adjust for your specific room.
The quick answer: room size to kW and BTU
For a typical apartment room with standard ceilings and average insulation, the rule of thumb is roughly 100 W of cooling per square meter. That maps onto the unit classes you will see in local stores:
| Room area | Cooling capacity | BTU class | Typical use |
|---|---|---|---|
| up to 20 m² | 2.5 kW | 9000 BTU | bedroom, small office |
| 20–35 m² | 3.5 kW | 12000 BTU | living room, larger bedroom |
| 35–50 m² | 5.0–5.5 kW | 18000 BTU | open-plan living room and kitchen |
| 50–70 m² | 7.0–7.5 kW | 24000 BTU | large open space, small premises |
These are the same size tiers installers on ORVIA use for their fixed installation prices (3.5, 5.5, and 7.5 kW), so once you know your class you can compare both the unit and the installation cost before deciding.
What changes the calculation
The 100 W/m² rule assumes an average room. Add roughly 10–20% capacity for each factor that applies: large windows facing south or west, a top-floor apartment under the roof, ceilings higher than 2.7 m, poor or old insulation, or a kitchen where appliances add heat. A room with two or more of these deserves the next size up; a shaded, well-insulated room with small windows can go one size down.
Many products listed by stores on ORVIA state a coverage area in square meters, so you can filter what fits your room directly instead of converting BTU in your head.
kW, BTU, and what the label actually says
Both numbers describe the same thing — how much heat the unit can move per hour. BTU is the imperial habit that stuck in shop listings; kW is what the EU energy label uses. The conversion is about 3412 BTU/h to 1 kW.
One common confusion: the kW on the label is cooling output, not what the unit draws from the socket. A modern 3.5 kW inverter unit typically consumes around 1 kW of electricity at full load, and much less once the room is at temperature — how much less is the inverter vs non-inverter question.
Why oversizing backfires
It feels safe to buy bigger, but an oversized AC reaches the set temperature before it has had time to pull moisture out of the air, then shuts off. The result is short on-off cycles, a room that is cold yet humid, more compressor wear, and more noise — plus a higher purchase price and a higher installation tier. Undersizing fails more predictably: the unit simply runs continuously and still falls behind on the hottest days. Correct sizing beats both.
Open-plan homes and multiple rooms
One unit cools the space it can see. An AC in the hallway does not meaningfully cool the bedrooms behind closed doors — for separate rooms, plan separate (smaller) units or a multi-split system with one outdoor unit. For an L-shaped or open-plan space, size for the total area and place the indoor unit where the airflow covers the longest axis. An installer can confirm placement during booking; positioning also affects the installation price through piping length.
From size to total budget
Your size class sets both numbers in the budget: the unit price and the installation tier. On ORVIA, stores list units with prices and coverage areas, and installers publish fixed installation prices per size class — so once you know whether your room is a 3.5, 5.5, or 7.5 kW case, the total cost is two lookups, not a guess.
Frequently asked questions
- Is 12000 BTU enough for 50 m²?
- Usually not for one open 50 m² space — 12000 BTU (about 3.5 kW) is comfortable up to roughly 35 m² in a typical apartment. For 50 m² look at the 18000 BTU (5.0–5.5 kW) class, or two smaller units if the space is split into rooms.
- What does BTU mean, and how does it convert to kW?
- BTU per hour is the imperial unit for cooling output; kilowatts are the metric one. Roughly 3412 BTU/h equals 1 kW, so 9000 BTU ≈ 2.5 kW, 12000 BTU ≈ 3.5 kW, 18000 BTU ≈ 5.3 kW, and 24000 BTU ≈ 7 kW. The kW figure on the label is cooling output, not electricity consumption.
- Is it better to buy a bigger AC just in case?
- No. An oversized unit cools the air faster than it can dehumidify it, switches on and off in short cycles, and leaves the room cold but clammy — while costing more to buy and install. Size to the room, not above it.