How many BTU do I need for a bedroom? (12x12 and other room sizes)
A 12 x 12 ft bedroom (144 sq ft) needs 5,000 BTU/h on the ENERGY STAR room air conditioner chart, a 5,000 BTU unit; bedrooms from 10 x 10 ft (100 sq ft) to 15 x 20 ft (300 sq ft) run from 5,000 BTU/h to 8,000 BTU/h. That is with an 8 ft ceiling, average sun and two people; a very sunny room adds 10 percent, each extra person 600 BTU. The tables below give eight bedroom sizes with the adjustments, the ceiling effect and the same rooms in m² and kW.
1. How many BTU for a 10x10, 10x12, 12x12 or 12x14 bedroom?
Each room below is looked up in the ENERGY STAR chart (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart) by its floor area, then the chart's own adjustments are applied: heavily shaded x0.9, very sunny x1.1, a third person +600 BTU. The unit class is the next chart capacity at or above the average-sun figure, not a product recommendation. Read at an 8 ft ceiling.
| Bedroom (ft) | Area (sq ft) | Chart BTU/h | Heavily shaded | Very sunny | Three people | kW | Unit class |
|---|---|---|---|---|---|---|---|
| 10 x 10 | 100 | 5,000 | 4,500 | 5,500 | 5,600 | 1.47 kW | 5,000 BTU unit |
| 10 x 12 | 120 | 5,000 | 4,500 | 5,500 | 5,600 | 1.47 kW | 5,000 BTU unit |
| 11 x 12 | 132 | 5,000 | 4,500 | 5,500 | 5,600 | 1.47 kW | 5,000 BTU unit |
| 12 x 12 | 144 | 5,000 | 4,500 | 5,500 | 5,600 | 1.47 kW | 5,000 BTU unit |
| 12 x 14 | 168 | 6,000 | 5,400 | 6,600 | 6,600 | 1.76 kW | 6,000 BTU unit |
| 13 x 15 | 195 | 6,000 | 5,400 | 6,600 | 6,600 | 1.76 kW | 6,000 BTU unit |
| 14 x 16 | 224 | 6,000 | 5,400 | 6,600 | 6,600 | 1.76 kW | 6,000 BTU unit |
| 15 x 20 | 300 | 8,000 | 7,200 | 8,800 | 8,600 | 2.34 kW | 8,000 BTU unit |
A 10 x 10 and a 12 x 12 bedroom get the same 5,000 BTU/h because both sit in the chart's first band; the step to 8,000 BTU/h comes with the 15 x 20 ft (300 sq ft) main bedroom. The AC BTU calculator does the lookup for your own dimensions, sun, people and ceiling, and shows tons and kW beside the BTU/h.
2. Does a sunny bedroom or a tall ceiling change the size?
Sun is in the chart: very sunny adds 10 percent, heavily shaded takes 10 percent off (table 1). The ceiling is not: the chart is read at 8 ft, and BTUtally scales the chart figure by height / 8 ft above that, which is our assumption, labelled as such (BTUtally assumption, not in the chart). A 12 x 12 bedroom with average sun and two people:
| Ceiling | BTU/h | Tons | kW | Unit class |
|---|---|---|---|---|
| 8 ft | 5,000 | 0.42 tons | 1.47 kW | 5,000 BTU unit |
| 9 ft | 5,625 | 0.47 tons | 1.65 kW | 6,000 BTU unit |
| 10 ft | 6,250 | 0.52 tons | 1.83 kW | 7,000 BTU unit |
From 5,000 BTU/h at 8 ft to 6,300 BTU/h at 10 ft: a tall ceiling moves a small bedroom up one unit class. A bedroom that is also a home office with a third person in it during the day takes the three-people column of table 1 instead.
3. How many BTU for a bedroom in square metres (and kW)?
The same chart in metric: m² is converted to sq ft before the lookup, and kW = BTU/h / 3,412 (Wikipedia, British thermal unit). Average sun, two people, a 2.4 m (8 ft) ceiling.
| Room (m²) | sq ft | BTU/h | kW | Tons |
|---|---|---|---|---|
| 10 | 108 | 5,000 | 1.47 kW | 0.42 tons |
| 12 | 129 | 5,000 | 1.47 kW | 0.42 tons |
| 15 | 161 | 6,000 | 1.76 kW | 0.50 tons |
| 20 | 215 | 6,000 | 1.76 kW | 0.50 tons |
| 25 | 269 | 7,000 | 2.05 kW | 0.58 tons |
| 30 | 323 | 8,000 | 2.34 kW | 0.67 tons |
A 10 m² box room and a 30 m² main bedroom span 1.47 kW to 2.34 kW of cooling. For the whole chart, from 100 to 2,500 sq ft, and the heating side in BTU per square foot, see how many BTU per square foot; a space larger than the chart is a central system, sized by the heat pump calculator and the Pro report room by room.
Frequently asked questions
- How many BTU do I need for a 12x12 bedroom?
- 5,000 BTU/h: 12 x 12 ft is 144 sq ft, inside the chart's "100 up to 150" band (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart). Heavily shaded, 4,500 BTU/h; very sunny, 5,500 BTU/h; three people, 5,600 BTU/h. A 5,000 BTU unit covers it.
- How many BTU do I need for a 10x10 bedroom?
- 5,000 BTU/h, the same as a 12 x 12: 10 x 10 ft is 100 sq ft, and the chart's first band runs from 100 to 150 sq ft. Below 100 sq ft the chart has no smaller figure, so a box room also gets 5,000 BTU/h, the smallest figure on the chart.
- How many BTU per square foot for a bedroom?
- About 35 BTU per sq ft in a 12 x 12 room and about 27 in a 15 x 20 one: the chart is not a flat rate, and small rooms get more per square foot because the walls and window are large relative to the floor. The guide on BTU per square foot has the whole chart.
- Does it matter how many people sleep in the bedroom?
- The chart counts 2 people and adds 600 BTU/h for each one beyond that (ENERGY STAR, Room Air Conditioners, sizing chart notes); one person in the room does not take anything off. Two adults and a child in a 12 x 12 bedroom: 5,600 BTU/h.
- Should I buy a 5,000 or a 6,000 BTU unit for a bedroom?
- The chart's answer for a bedroom under 150 sq ft with average sun and two people is 5,000 BTU/h. It becomes the next band's 6,000 BTU/h as soon as the room is 150 sq ft or larger, and the calculator names a 6,000 BTU unit for a 12 x 12 that is very sunny (5,500 BTU/h) or has a 9 ft ceiling (5,600 BTU/h). The chart does not add a margin for a bigger unit, and neither does the calculator.
- Is a portable air conditioner sized the same way as a window unit?
- The ENERGY STAR chart is for room air conditioners and does not distinguish window, through-the-wall or portable units, so the BTU figure is the same; what differs is how much of the rated capacity reaches the room, which the chart does not cover. One ton of cooling is 12,000 BTU/h (Wikipedia, British thermal unit), so a bedroom unit is 0.42 tons to 0.67 tons.
More guides
- How many BTU do I need per square foot? (room size chart)
The ENERGY STAR room size to BTU chart with its adjustments, heating BTU and tons by home size and climate zone, and m² to kW at three insulation levels.
- What size heat pump do I need for 2,000 sq ft? (tons by climate zone)
Heating BTU/h and heat pump tons for 2,000 sq ft in every US climate zone and insulation level, the half-ton class by home size and zone, and the same rule in m² and kW.
- What size boiler do I need? (UK combi and system kW by bedrooms and bathrooms)
Combi and system boiler kW for every bedrooms and bathrooms pair from the UK installers' tables, how many radiators a 24, 28 or 32 kW combi serves, and heat loss vs kW.
Last updated 2026-09-21. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.