How many BTU do I need? Room size chart
ENERGY STAR's chart for window and through-the-wall air conditioners. The capacities assume an 8-foot ceiling and are before any adjustment for sun, people or a kitchen.
| Room size | BTU per hour | Kilowatts | Tons |
|---|---|---|---|
| 100 to 150 sq ft9.3 to 13.9 m² | 5,000 | 1.47 | 0.42 |
| 150 to 250 sq ft13.9 to 23.2 m² | 6,000 | 1.76 | 0.50 |
| 250 to 300 sq ft23.2 to 27.9 m² | 7,000 | 2.05 | 0.58 |
| 300 to 350 sq ft27.9 to 32.5 m² | 8,000 | 2.34 | 0.67 |
| 350 to 400 sq ft32.5 to 37.2 m² | 9,000 | 2.64 | 0.75 |
| 400 to 450 sq ft37.2 to 41.8 m² | 10,000 | 2.93 | 0.83 |
| 450 to 550 sq ft41.8 to 51.1 m² | 12,000 | 3.52 | 1.00 |
| 550 to 700 sq ft51.1 to 65.0 m² | 14,000 | 4.10 | 1.17 |
| 700 to 1,000 sq ft65.0 to 93 m² | 18,000 | 5.28 | 1.50 |
| 1,000 to 1,200 sq ft93 to 111 m² | 21,000 | 6.15 | 1.75 |
| 1,200 to 1,400 sq ft111 to 130 m² | 23,000 | 6.74 | 1.92 |
| 1,400 to 1,500 sq ft130 to 139 m² | 24,000 | 7.03 | 2.00 |
| 1,500 to 2,000 sq ft139 to 186 m² | 30,000 | 8.79 | 2.50 |
| 2,000 to 2,500 sq ft186 to 232 m² | 34,000 | 9.96 | 2.83 |
To get square footage, multiply the room's length by its width in feet. ENERGY STAR's advice for odd shapes: a triangular area is length times width divided by two, and an L-shaped or irregular room can be split into rectangles and triangles and added up. Convert inches to fractions of a foot first, so 12 feet 6 inches is 12.5 feet.
Examples
| Room | Chart | Adjusted |
|---|---|---|
| Bedroom, 12 × 14 ft, average sun, 2 people | 6,000 | 6,000 BTU |
| Living room, 15 × 20 ft, very sunny, 4 people | 7,000 | 8,900 BTU |
| Kitchen, 12 × 15 ft, average sun, 2 people | 6,000 | 10,000 BTU |
| Home office, 10 × 12 ft, heavily shaded, 1 person | 5,000 | 4,500 BTU |
BTU per square foot
There is no single BTU-per-square-foot figure in ENERGY STAR's chart. It works out to about 33 to 50 BTU per square foot for the smallest rooms and falls as rooms get bigger, to roughly 14 to 17 for the largest. Dividing each row's capacity by the ends of its range:
| Room size | Capacity | BTU per sq ft | Watts per m² |
|---|---|---|---|
| 100–150 sq ft | 5,000 | 33–50 | 105–158 |
| 150–250 sq ft | 6,000 | 24–40 | 76–126 |
| 250–300 sq ft | 7,000 | 23–28 | 74–88 |
| 300–350 sq ft | 8,000 | 23–27 | 72–84 |
| 350–400 sq ft | 9,000 | 23–26 | 71–81 |
| 400–450 sq ft | 10,000 | 22–25 | 70–79 |
| 450–550 sq ft | 12,000 | 22–27 | 69–84 |
| 550–700 sq ft | 14,000 | 20–25 | 63–80 |
| 700–1,000 sq ft | 18,000 | 18–26 | 57–81 |
| 1,000–1,200 sq ft | 21,000 | 18–21 | 55–66 |
| 1,200–1,400 sq ft | 23,000 | 16–19 | 52–60 |
| 1,400–1,500 sq ft | 24,000 | 16–17 | 50–54 |
| 1,500–2,000 sq ft | 30,000 | 15–20 | 47–63 |
| 2,000–2,500 sq ft | 34,000 | 14–17 | 43–54 |
A single BTU-per-square-foot rule ignores how the chart changes with room size, and the Department of Energy warns that rule-of-thumb sizing too often leads to oversized systems.
How many square feet does a 5,000, 8,000, 10,000 or 12,000 BTU AC cool?
These are the capacities with at least 20 models on ENERGY STAR's list of 570 certified room air conditioners, with the room size ENERGY STAR's chart gives each one:
| Air conditioner | Room size (chart) | Certified models |
|---|---|---|
| 5,000 BTU | 100 to 150 sq ft9.3 to 13.9 m² | 21 |
| 6,000 BTU | 150 to 250 sq ft13.9 to 23.2 m² | 29 |
| 8,000 BTU | 300 to 350 sq ft27.9 to 32.5 m² | 99 |
| 10,000 BTU | 400 to 450 sq ft37.2 to 41.8 m² | 108 |
| 12,000 BTU | 450 to 550 sq ft41.8 to 51.1 m² | 129 |
| 14,000 BTU | 550 to 700 sq ft51.1 to 65.0 m² | 43 |
| 18,000 BTU | 700 to 1,000 sq ft65.0 to 93 m² | 27 |
| 24,000 BTU | 1,400 to 1,500 sq ft130 to 139 m² | 28 |
- A 5,000 BTU air conditioner is for 100 to 150 sq ft, a small bedroom or office.
- An 8,000 BTU air conditioner is for 300 to 350 sq ft, such as a 16 × 20 ft room.
- A 10,000 BTU air conditioner is for 400 to 450 sq ft.
- A 12,000 BTU air conditioner (one ton) is for 450 to 550 sq ft.
These assume average sun, two people and an 8-foot ceiling. A sunny room, more people or a kitchen shrinks the area each size covers.
Adjusting for sun, people and kitchens
ENERGY STAR adjusts its chart in four cases:
- Heavily shaded room: reduce capacity by 10%.
- Very sunny room: increase capacity by 10%.
- More than two people regularly in the room: add 600 BTU for each extra person.
- Kitchen: add 4,000 BTU.
The calculator applies the sun adjustment to the chart capacity, then adds people and kitchen on top. ENERGY STAR also suggests thinking about where the unit goes: near a corner, pick one that can direct its airflow into the room.
What about high ceilings?
ENERGY STAR says its capacities are calculated for an 8-foot ceiling and that a room with higher ceilings may need a larger unit. It does not say how much larger, and we did not find a government or standards-body figure, so the calculator does not change the number for ceiling height. With a ceiling above 8 feet it points you to the next common size up instead.
Is a bigger air conditioner better?
No. ENERGY STAR notes that a unit that is too big is less effective and less efficient: it cools the room before it has removed the humidity, leaving the air cool but damp and clammy. Its advice is to match the unit to the room's square footage. ENERGY STAR also points out that variable-speed (inverter) models vary their compressor speed to hold the temperature rather than switching fully on and off.
What size air conditioner do I need? Our picks by room size
The window units in our air conditioner guide, with the room size ENERGY STAR's chart gives for their rated capacity:
| Model | Capacity | Room size (chart) | CEER |
|---|---|---|---|
| Midea U MAW08V1QWTBest overall, variable speed | 8,000 BTU | Up to 350 sq ft32.5 m² | 15 |
| GE Profile ClearView PHNT10CCBest for large rooms, variable speed | 10,300 BTU | Up to 450 sq ft41.8 m² | 14.7 |
| Frigidaire FHWW084TE1Best budget, single speed | 8,000 BTU | Up to 350 sq ft32.5 m² | 10.9 |
The 8,000 BTU Midea U and Frigidaire suit a bedroom or office up to about 350 sq ft. The GE Profile ClearView's 10,300 BTU covers the 10,000 BTU row, rooms up to about 450 sq ft. A very sunny 350 sq ft living room comes to 8,800 BTU, more than the 8,000 BTU units, so the GE is the better fit there. Capacities and CEER for the Midea and GE are from ENERGY STAR's certified list; the Frigidaire's are from Frigidaire.
Window vs portable vs mini-split sizing
Window and through-the-wall units
ENERGY STAR's chart is written for these "room air conditioners", and their capacity is measured under the Department of Energy's room air conditioner test. Use the chart as is.
Portable air conditioners: SACC vs ASHRAE BTU
Portable units often carry two BTU numbers. Since November 28, 2016, the Department of Energy has required portable air conditioner ratings to use its own test, which reports a "seasonally adjusted cooling capacity" (SACC). DOE found that the net cooling of portable units is generally much lower than the older industry test suggested, mostly because of warm outside air leaking back into the room. Some makers, LG among them, still list the older ASHRAE figure next to it:
- LG LP0825WFR: 8,000 BTU (SACC) / 11,000 BTU (ASHRAE), 27% lower on DOE's test.
- LG LP1419IVSM: 10,000 BTU (SACC) / 14,000 BTU (ASHRAE), 29% lower.
LG says the DOE rating can be up to 42% lower than the ASHRAE rating for the same product. Compare a portable's SACC with the chart above, not its ASHRAE number. LG's own room sizes line up that way: it rates the 8,000 BTU (SACC) LG LP0825WFR for up to 350 sq ft and the 10,000 BTU (SACC) LG LP1419IVSM for up to 450 sq ft, the same as ENERGY STAR's 8,000 and 10,000 BTU rows.
Mini-split size calculator
Ductless mini-splits are rated in BTU per hour or tons, so the tables below convert them. We did not find a mini-split square-footage chart from a manufacturer or from ACCA, the contractors' standards body, that we could verify, so this calculator does not give one. ENERGY STAR's chart is for room air conditioners and covers cooling only; a mini-split heat pump has to meet the heating load as well. ACCA's Manual J load calculation is the method the Department of Energy points to for sizing heating and cooling equipment.
Whole-house and central AC: use Manual J
For a whole house, a square-foot chart is the wrong tool. ACCA's Manual J (8th edition) is the ANSI-recognized standard for residential heating and cooling loads, and ACCA notes that national building codes and most state and local jurisdictions require a Manual J calculation. It uses outdoor design conditions for your location along with the house itself. The Department of Energy warns that rules of thumb too often produce oversized systems that cost more, waste energy and cycle on and off too often. Ask your HVAC contractor for the Manual J report.
BTU to watts
One BTU per hour is 0.2931 watts, so a 10,000 BTU air conditioner moves about 2,931 watts (2.93 kW) of heat. To go the other way, one watt is 3.412 BTU per hour.
- watts
- 3,517
- kW
- 3.52
- tons
- 1.00
| BTU per hour | Watts | Kilowatts |
|---|---|---|
| 5,000 | 1,465 | 1.47 |
| 6,000 | 1,758 | 1.76 |
| 8,000 | 2,345 | 2.34 |
| 10,000 | 2,931 | 2.93 |
| 12,000 | 3,517 | 3.52 |
| 14,000 | 4,103 | 4.10 |
| 18,000 | 5,275 | 5.28 |
| 24,000 | 7,034 | 7.03 |
| 36,000 | 10,551 | 10.55 |
That is cooling output, not the electricity the unit uses. Room air conditioner efficiency is rated as CEER, in BTU per watt-hour, so capacity divided by CEER gives a rough idea of the power draw while it runs: about 533 W for the Midea U MAW08V1QWT, 701 W for the GE Profile ClearView PHNT10CC and 734 W for the Frigidaire FHWW084TE1. CEER also counts standby power, so treat these as approximate.
Heater BTU: watts to BTU for space heaters
Electric space heaters are rated in watts. Converting at NIST's factor:
| Heater | BTU per hour |
|---|---|
| 500 W | 1,706 |
| 750 W | 2,559 |
| 1,000 W | 3,412 |
| 1,500 W | 5,118 |
ENERGY STAR's chart is for cooling only, and we did not find a government heating-per-square-foot figure we could verify, so this page does not size heaters by room. Heating a whole house is a Manual J job.
BTU to tons
A ton of cooling, or ton of refrigeration, is 12,000 BTU per hour (3,516.853 W in NIST's tables). Central systems and mini-splits are often described in tons.
| Tons | BTU per hour | Kilowatts |
|---|---|---|
| 0.5 | 6,000 | 1.76 |
| 0.75 | 9,000 | 2.64 |
| 1 | 12,000 | 3.52 |
| 1.5 | 18,000 | 5.28 |
| 2 | 24,000 | 7.03 |
| 2.5 | 30,000 | 8.79 |
| 3 | 36,000 | 10.55 |
| 3.5 | 42,000 | 12.31 |
| 4 | 48,000 | 14.07 |
| 5 | 60,000 | 17.58 |
How this calculator works
- Room size is length times width, converted to square feet if you enter meters. It finds the matching row in ENERGY STAR's chart; a room exactly on a boundary, such as 150 sq ft, uses the lower row. Rooms under 100 sq ft get the smallest size, 5,000 BTU. The chart stops at 2,500 sq ft.
- Adjustments are ENERGY STAR's: ±10% for heavy shade or strong sun, 600 BTU for each regular occupant over two, and 4,000 BTU for a kitchen.
- Look for is the smallest capacity at or above your estimate among the sizes with at least 20 models on ENERGY STAR's certified list: 5,000, 6,000, 8,000, 10,000, 12,000, 14,000, 18,000, 24,000 BTU. Only 6 certified models are larger than 24,000 BTU.
- No climate setting. ENERGY STAR's chart has no climate adjustment, and we did not find a published one from a government or standards body. Manual J handles climate through outdoor design conditions.
- Conversions use NIST's factors: 1 BTU per hour = 0.2930711 W, and 1 ton of refrigeration = 12,000 BTU per hour = 3,516.853 W.
Shopping for a unit? See our window air conditioner picks. Sources were checked on October 7, 2026.
Sources
- ENERGY STAR, Room Air Conditioners: "Properly Sized Room Air Conditioners" chart (100–150 sq ft = 5,000 BTU/h through 2,000–2,500 sq ft = 34,000 BTU/h, based on an 8-foot ceiling) and adjustments for shade, sun, occupants and kitchens. www.energystar.gov/products/room_air_conditioners
- ENERGY STAR Certified Room Air Conditioners dataset (cooling capacity, CEER, annual energy use for 570 certified models). data.energystar.gov/Active-Specifications/ENERGY-STAR-Certified-Room-Air-Conditioners/5xn2-dv4h
- ENERGY STAR product finder, Midea MAW08V1QWT: 8,000 BTU/h, CEER 15, variable-speed compressor, 400 kWh/yr. www.energystar.gov/productfinder/product/certified-room-air-conditioners/details/2620516
- ENERGY STAR product finder, GE Profile PHNT10CCH1: 10,300 BTU/h, CEER 14.7, variable-speed compressor, 525.5 kWh/yr. www.energystar.gov/productfinder/product/certified-room-air-conditioners/details/2684130
- Frigidaire FHWW084TE1 product page: 8,000 BTU, 251–350 sq ft, combined energy efficiency ratio 10.9. www.frigidaire.com/en/p/home-comfort/air-conditioners/window-mounted-air-conditioners/FHWW084TE1
- U.S. Department of Energy, Energy Conservation Program: Test Procedures for Portable Air Conditioners, final rule, 81 FR 35242 (June 1, 2016). Introduces the seasonally adjusted cooling capacity (SACC); mandatory for representations from November 28, 2016. www.federalregister.gov/documents/2016/06/01/2016-12446/energy-conservation-program-test-procedures-for-portable-air-conditioners
- LG LP0825WFR: 8,000 BTU (SACC) / 11,000 BTU (ASHRAE). LG notes the DOE rating "may be up to 42% lower" than the older ASHRAE rating. www.lg.com/us/air-conditioners/lg-lp0825wfr-portable-air-conditioner
- LG LP1419IVSM: 10,000 BTU (SACC) / 14,000 BTU (ASHRAE). www.lg.com/us/air-conditioners/lg-LP1419IVSM-portable-air-conditioner
- Electronic Code of Federal Regulations, 10 CFR 430 Subpart B, Appendix F (room air conditioner test method): cooling capacity in Btu/h; combined energy efficiency ratio (CEER) in Btu per watt-hour. www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-B/appendix-Appendix%20F%20to%20Subpart%20B%20of%20Part%20430
- U.S. Department of Energy, Building Science Education: Proper Sizing of HVAC Systems (rules of thumb lead to oversized systems; use ACCA Manual J load calculations). bsesc.energy.gov/energy-basics/hvac-proper-sizing-hvac-systems
- Air Conditioning Contractors of America, Manual J Residential Load Calculation, 8th Edition (ANSI/ACCA 2 Manual J – 2016). www.acca.org/standards/technical-manuals/manual-j
- NIST Special Publication 811, Appendix B.9: 1 Btu_IT/h = 0.2930711 W; 1 ton of refrigeration (12,000 Btu_IT/h) = 3,516.853 W. www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9