Air Conditioner Sizes: BTU Chart by Room Size and Unit Dimensions
How much cooling capacity a room needs, how to adjust for sun, people and kitchens, and how big window, portable, through-the-wall and mini-split units are once you have picked a capacity.
ENERGY STAR's chart works out to roughly 20 to 25 BTU per hour per square foot for most rooms: a 150 to 250 sq ft room (14 to 23 m²) needs 6,000 BTU, 350 to 400 sq ft (33 to 37 m²) needs 9,000 BTU, and 450 to 550 sq ft (42 to 51 m²) needs 12,000 BTU. Add 10% for a very sunny room, 600 BTU for each regular occupant beyond two, and 4,000 BTU for a kitchen.
- 150-250 sq ft
- 6,000 BTU
- 350-400 sq ft
- 9,000 BTU
- 450-550 sq ft
- 12,000 BTU
- 1 ton
- 12,000 BTU/h (3.5 kW)
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Air conditioner size chart by room size
This is the US EPA's ENERGY STAR chart for room air conditioners. It assumes an 8 ft (2.4 m) ceiling, average insulation and sun, and up to two people. The metric and kilowatt columns are conversions (1 sq ft = 0.0929 m², 1 kW = 3,412 BTU/h).
| Room area (sq ft) | Room area (m²) | Capacity (BTU/h) | Capacity (kW) |
|---|---|---|---|
| 100 to 150 | 9.3 to 13.9 | 5,000 | 1.5 |
| 150 to 250 | 13.9 to 23.2 | 6,000 | 1.8 |
| 250 to 300 | 23.2 to 27.9 | 7,000 | 2.1 |
| 300 to 350 | 27.9 to 32.5 | 8,000 | 2.3 |
| 350 to 400 | 32.5 to 37.2 | 9,000 | 2.6 |
| 400 to 450 | 37.2 to 41.8 | 10,000 | 2.9 |
| 450 to 550 | 41.8 to 51.1 | 12,000 | 3.5 |
| 550 to 700 | 51.1 to 65.0 | 14,000 | 4.1 |
| 700 to 1,000 | 65.0 to 92.9 | 18,000 | 5.3 |
| 1,000 to 1,200 | 92.9 to 111.5 | 21,000 | 6.2 |
| 1,200 to 1,400 | 111.5 to 130.1 | 23,000 | 6.7 |
| 1,400 to 1,500 | 130.1 to 139.4 | 24,000 | 7.0 |
| 1,500 to 2,000 | 139.4 to 185.8 | 30,000 | 8.8 |
| 2,000 to 2,500 | 185.8 to 232.3 | 34,000 | 10.0 |
To find the area, multiply the room's length by its width: a 14 × 16 ft bedroom is 224 sq ft and needs 6,000 BTU; a 20 × 25 ft open living area is 500 sq ft and needs 12,000 BTU. For an L-shaped room, split it into two rectangles and add them.
Adjustments for sun, people, kitchens and ceilings
ENERGY STAR gives four corrections to the chart figure:
- Heavily shaded room: reduce capacity by 10%.
- Very sunny room: increase capacity by 10%.
- More than two regular occupants: add 600 BTU for each extra person.
- Kitchen: add 4,000 BTU for the heat from cooking.
Worked example: a sunny 320 sq ft family room used by three people starts at 8,000 BTU, becomes 8,800 BTU with the sun correction, and 9,400 BTU with one extra person, so a 10,000 BTU unit is the right choice. The chart assumes 8 ft ceilings, so for a 10 ft ceiling, which holds 25% more air, lean toward the next size up.
An air conditioner that is too big for the room cools the air before it has had time to pull out moisture, then cycles off. The result is a cold, damp room and higher bills. If the adjusted figure falls between two sizes, pick the closer one, and only go up when the room is sunny, has high ceilings or opens into another space.
Portable air conditioner sizing chart
Portable units sit inside the room, so some of the heat they remove leaks back in through the cabinet and the exhaust hose, and single-hose models pull warm outside air into the room to replace the air they blow out. For that reason the US Department of Energy test procedure rates them with a Seasonally Adjusted Cooling Capacity (SACC), which is lower than the older ASHRAE rating still printed on many boxes.
| Room area | SACC needed | Typical ASHRAE label |
|---|---|---|
| Up to 250 sq ft (23 m²) | 5,000 to 6,000 BTU | 8,000 to 10,000 BTU |
| 250 to 350 sq ft (23 to 33 m²) | 7,000 to 8,000 BTU | 10,000 to 14,000 BTU |
| 350 to 450 sq ft (33 to 42 m²) | 9,000 to 10,000 BTU | 14,000 BTU and up |
| 450 to 550 sq ft (42 to 51 m²) | 12,000 BTU | Beyond most portables; consider a window unit or mini-split |
The SACC column follows the ENERGY STAR room chart. The relationship between SACC and ASHRAE ratings varies by model: on many single-hose units the SACC is about 25 to 45% lower than the ASHRAE figure, and some dual-hose inverter models lose much less. Read both numbers rather than relying on the right-hand column.
- Unit size: about 17 to 19 in wide, 28 to 31 in tall and 13 to 17 in deep (43 to 48 × 71 to 79 × 33 to 43 cm), and 50 to 80 lb.
- Exhaust hose: about 5 to 6 in (13 to 15 cm) in diameter and 5 to 7 ft long. Keep it short and straight; a stretched or kinked hose cuts cooling.
- Window kit: sliding panels that typically cover openings from about 20 in to 46 in or more; casement and sliding windows need a different kit.
Window air conditioner dimensions
Window units hang half outside the window, so the two sizes that matter are the cabinet's front (width and height) and the window opening it needs. Ranges are typical of current models from the main brands.
| Capacity | Typical unit size (in) | Typical unit size (cm) | Window width | Weight |
|---|---|---|---|---|
| 5,000 to 6,000 BTU | 15 to 16.5 × 12 to 12.5 × 12 to 16 | 38 to 42 × 30 to 32 × 30 to 41 | about 21 to 36 in | 35 to 45 lb |
| 8,000 BTU | 18.5 to 19.5 × 12.5 to 14 × 15.5 to 20 | 47 to 50 × 32 to 36 × 39 to 51 | about 23 to 36 in | 45 to 60 lb |
| 10,000 to 12,000 BTU | 19 to 24 × 14 to 15.5 × 18 to 23 | 48 to 61 × 36 to 39 × 46 to 58 | about 26 to 41 in | 60 to 80 lb |
| 14,000 to 18,000 BTU | 23.5 to 26 × 15.5 to 18 × 22 to 28 | 60 to 66 × 39 to 46 × 56 to 71 | about 28 to 41 in | 85 to 120 lb |
| 24,000 to 25,000 BTU | 26 to 28 × 17.5 to 19 × 28 to 31 | 66 to 71 × 44 to 48 × 71 to 79 | about 30 to 42 in | 130 to 160 lb |
The window's clear height also matters: most double-hung windows need an opening of at least 13 to 18 in tall, depending on the unit, with the sash closed down onto the top of the cabinet. Accordion side panels fill the gap between the unit and the window frame. Standard window sizes are in the window size guide, and combined door and window openings in the doors and windows guide.
Through-the-wall and mini-split unit sizes
Through-the-wall air conditioners
Wall units slide into a metal sleeve built into the wall. Common sleeves are about 24 or 26 in wide and 14 to 16 in tall, but each brand's sleeve differs slightly. A replacement must match the existing sleeve's inside dimensions, or the sleeve has to be replaced, which means opening up the wall. Capacities typically run from 8,000 to 14,000 BTU.
Ductless mini-split indoor units
Wall-mounted mini-split heads are wide and shallow. Sizes vary by brand, but typical ranges are:
| Capacity | Width | Height | Depth |
|---|---|---|---|
| 9,000 to 12,000 BTU | 30 to 33 in 76 to 84 cm | 11 to 12 in 28 to 30 cm | 8 to 9 in 20 to 23 cm |
| 18,000 BTU | 35 to 40 in 89 to 102 cm | 12 to 13 in | 9 to 10 in |
| 24,000 BTU | 38 to 43 in 97 to 109 cm | 12 to 13.5 in | 9.5 to 10.5 in |
Most heads need about 6 in (15 cm) of clear space above for air intake and a few inches at each side, so a 12,000 BTU head takes roughly 40 × 18 in of wall. The outdoor unit for a single-zone system is typically 28 to 35 in wide and 21 to 28 in tall.
Central air conditioner sizes (tons)
Central systems are rated in tons. One ton of cooling is 12,000 BTU/h (3.5 kW), the rate of cooling once defined by melting a ton of ice in a day. Residential systems run from 1.5 to 5 tons.
| Tons | BTU/h | kW |
|---|---|---|
| 1.5 | 18,000 | 5.3 |
| 2 | 24,000 | 7.0 |
| 2.5 | 30,000 | 8.8 |
| 3 | 36,000 | 10.6 |
| 3.5 | 42,000 | 12.3 |
| 4 | 48,000 | 14.1 |
| 5 | 60,000 | 17.6 |
The room chart above does not scale up reliably to a whole house, because insulation, windows, air leakage and climate dominate. The International Residential Code (M1401.3) requires heating and cooling equipment to be sized with ACCA Manual S, based on loads calculated with ACCA Manual J. Ask the installer for the Manual J figure rather than accepting a size based on square footage alone.
Power supply by size
- Up to about 12,000 to 15,000 BTU: most window and portable units run on a standard 115 V outlet and draw up to about 12 A. Use a dedicated circuit where possible.
- Around 15,000 to 18,000 BTU: some 115 V models need a 20 A circuit with a NEMA 5-20 outlet (one horizontal blade).
- 18,000 BTU and up: usually 208/230 V, with a matching outlet that a 115 V plug will not fit.
- Mini-splits and central systems: hard-wired, typically 208/230 V, installed by an electrician or HVAC contractor.
Window and portable units sold in the US come with a safety plug (LCDI) on the cord. Do not use an extension cord: the plug is designed to go straight into the wall outlet.
Frequently asked questions
What size portable air conditioner do I need?
Use the SACC (Seasonally Adjusted Cooling Capacity) figure on the box, not the larger ASHRAE figure, and match it to the room-size chart. A room of 300 to 350 sq ft needs about 8,000 BTU SACC, which usually means a unit marketed as 12,000 to 14,000 BTU (ASHRAE).
What size air conditioner do I need for a 12 × 12 room?
A 12 × 12 ft room is 144 sq ft (13.4 m²), so ENERGY STAR's chart calls for 5,000 BTU. If the room is very sunny or is a home office with equipment running, step up to 6,000 BTU.
How many square feet does a 12,000 BTU air conditioner cool?
About 450 to 550 sq ft (42 to 51 m²) under the ENERGY STAR chart, assuming an 8 ft ceiling, average sun and up to two people. In a kitchen, the same room would need about 16,000 BTU.
How many BTU is 1 HP in an aircon?
In the air-conditioning trade in much of Asia, 1 HP is used as shorthand for about 9,000 BTU/h of cooling, 1.5 HP for about 12,000 BTU/h, 2 HP for about 18,000 and 2.5 HP for about 24,000. It is a label, not a conversion: one mechanical horsepower is only 2,544 BTU/h. Check the BTU or kW rating on the unit.
Is a bigger air conditioner better?
No. An oversized unit cools the air quickly and switches off before it has removed much moisture, so the room feels cool but clammy, and frequent cycling wastes energy. Stick to the chart and the adjustments, and choose the next size up only when you fall between sizes.
How big is a window air conditioner?
A 5,000 to 6,000 BTU window unit is typically about 15 to 16.5 in wide, 12 to 12.5 in tall and 12 to 16 in deep, and fits windows from about 21 to 23 in wide. A 12,000 BTU unit is closer to 19 to 24 in wide, 14 to 15.5 in tall and 18 to 23 in deep.