IndoorComfortKit 
Reading the room AC capacity estimate
Use this AC BTU calculator to estimate cooling capacity for a single room, bedroom, office, or small connected area. The result is a planning number for comparing nearby room air conditioner classes, not a product approval.
The AC BTU result is an adjusted planning capacity for a single room or a small connected area. Floor area selects an ENERGY STAR capacity band; sun, shade, extra occupants, and kitchen heat adjust that value. Ceiling height appears as a limitation when it differs from the table’s 8-foot assumption. It is not a full HVAC design.
Read the number alongside comfort symptoms. If a room cools quickly but still feels damp, the unit may be short-cycling or the room may need moisture control. If a room never reaches the target temperature during direct sun, capacity, shading, air sealing, or heat sources may be the issue. Use the Indoor Comfort Score Calculator to separate temperature from humidity, and check why an oversized AC feels humid before assuming bigger is better.
The result does not prove that a unit will perform well in every installation. Window fit, air leakage, insulation, shade, ceiling fans, filter condition, and door position all matter. Portable single-hose units can also behave differently from window units because they may pull conditioned air out of the room.
Planning estimate only. Not a Manual J load calculation, electrical review, installation approval, or manufacturer recommendation.
How the ENERGY STAR room AC chart is applied
Read the calculation details and assumptions
The capacities come from ENERGY STAR’s room air conditioner table, which assumes an 8-foot ceiling. Its adjacent ranges share endpoints. This site assigns a shared endpoint to the higher area band: exactly 150 sq ft starts at 6,000 BTU/h and exactly 250 sq ft starts at 7,000 BTU/h. This boundary convention belongs to IndoorComfortKit. Areas below 100 or above 2,500 sq ft receive an out-of-table message, not an extrapolated size.
Apply shade or sun first: subtract 10% for a heavily shaded room or add 10% for a very sunny room. Then add 600 BTU/h per usual occupant above two, and 4,000 BTU/h for kitchen heat. Normal exposure has no adjustment. The calculator displays whole BTU/h without rounding to a product class or forcing a 5,000-BTU floor.
Ceiling height is recorded as context. A height other than 8 feet triggers a caution; there is no published height multiplier in this table, so the calculator does not invent one. Compare the result with product guidance or a room-specific load assessment.
Worked AC examples
These are hypothetical arithmetic checks, not household cooling trials.
| Room condition | Table capacity | Adjusted result |
|---|---|---|
| 180 sq ft, shaded, one occupant | 6,000 BTU/h | 5,400 BTU/h |
| 240 sq ft, sunny, one occupant | 6,000 BTU/h | 6,600 BTU/h |
| 320 sq ft, normal sun, two occupants, kitchen | 8,000 BTU/h | 12,000 BTU/h |
| 500 sq ft, normal sun, four occupants | 12,000 BTU/h | 13,200 BTU/h |
Room-size BTU chart before adjustments
For the complete 100–2,500 sq ft reference, open the BTU-to-square-feet chart. On this page, enter your room details to see the base band and the adjustments together. A raw chart value and an adjusted result answer different questions; neither is an installation approval.
Room AC estimates for different spaces
A bedroom at night often has low sun load and one or two occupants. A modest BTU estimate may work if the door can stay partly open or air can return to the unit.
A sunny home office may need more capacity than its square footage suggests. Afternoon sun, a computer, monitors, and closed blinds that still radiate heat can push the room above a simple area estimate.
A small apartment may act like one connected cooling zone. If the AC is expected to cool a bedroom, living area, and kitchen, measure the connected area instead of only the room where the unit sits.
A kitchen or studio with cooking heat needs extra caution. A small AC can be overwhelmed during cooking even if it feels adequate at other times.
Before selecting a room air conditioner
Measure the real cooled area. Include open connected spaces and exclude rooms behind closed doors unless air moves freely.
Reduce heat before increasing BTU. Add shade, close blinds before sun hits the glass, seal obvious gaps around the unit, and turn off unused electronics.
Improve air mixing. A fan can move cooled air across a long room and reduce hot pockets without changing AC size.
Check humidity separately. If the room reaches temperature but feels clammy, use the Indoor Humidity Calculator and consider whether runtime is too short.
Compare nearby sizes, not just the biggest option. A slightly undersized unit may run longer during peaks, while a much oversized unit may cycle quickly. For damp rooms, the Dehumidifier Size Calculator may be the better next check.
AC sizing inputs to measure again
Measure the cooled area, not only the floor under the unit. If the bedroom door is usually open to a hall or office, include the connected area that air can reach. If doors stay closed, do not include those rooms.
Do not leave ceiling height blank or guess very high. Tall rooms change the amount of air and surface area being cooled. Also check sun exposure honestly: a west-facing room with afternoon glass can behave differently from a shaded room with the same square footage.
Avoid using the result as a direct product recommendation. Product labels, window fit, electrical requirements, installation limits, and local rules still matter.
What a room AC estimate cannot check
This calculator cannot perform a Manual J load calculation, inspect electrical capacity, approve window support, evaluate insulation, or guarantee runtime and humidity control. It also cannot model portable AC hose losses, unusual glass, or heat from large equipment.
This calculator is not medical advice, building inspection advice, HVAC engineering advice, or safety certification. It does not replace a load calculation, electrical review, manufacturer instructions, lease rules, or local code. Use qualified help for permanent equipment, unusual electrical loads, structural window concerns, or whole-home cooling decisions.
Compare the estimate with a product rating
Compare the result with nearby product size classes and manufacturer room guidance. If the room reaches temperature but still feels damp, review why an oversized AC feels humid and check humidity separately with the Indoor Humidity Calculator. If the room never cools during sun, shading and air sealing may matter before buying a larger unit.
Common questions
How many BTU do I need for a 10x12 room?
A 10x12 room is 120 square feet. The ENERGY STAR area table starts this room at 5,000 BTU/h before shade, sun, extra occupants, or kitchen adjustments. Check the 8-foot ceiling assumption and manufacturer guidance.
Is 5,000 BTU enough for a bedroom?
It can be enough for many small shaded bedrooms if the door position, window fit, and heat sources are reasonable. A sunny bedroom, high ceiling, connected office, or poor window seal may need a higher class.
Is a bigger AC always better?
No. A much larger unit may cool quickly and run for shorter cycles, which can leave humidity behind. Compare nearby sizes and watch comfort, runtime, and room humidity together.
Sources and method notes
Read the full source registry, formulas, site-defined rules, and method notes.