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About this tool
Find the right AC tonnage for a bedroom from floor area, ceiling height, roof exposure, sunlight and how many people sleep in it.
The Bedroom AC Tonnage Calculator estimates the cooling load of a bedroom in BTU per hour and converts it to air-conditioner tonnage, where one ton of refrigeration equals 12,000 BTU/hr. It starts from a base load of about 80 BTU/hr per square foot at a 10 ft ceiling under Indian summer design conditions, then applies the standard field corrections: ceiling height, a sun-exposed roof overhead, window sun exposure, climate zone, occupants beyond two at 600 BTU/hr each, and the waste heat of electronics at 3.41 BTU/hr per watt. The result is rounded up to the nearest capacity actually sold — 0.8, 1, 1.5, 2 or 2.5 ton.
Open Bedroom AC Tonnage Calculator on AltFTool — it loads instantly in your browser.
Fill Room length (ft), Room width (ft), Ceiling height (ft), People sleeping in the room and Electronics left running in the room (watts).
Choose Sun exposure and Climate, and tick Top floor with a sun-exposed roof directly above when a sun-baked slab sits over the bedroom.
Read the Recommended AC size in tons alongside the BTU/hr load and every multiplier, then press Copy result.
A sun-baked slab directly overhead adds roughly 15% to the load — the single biggest reason top-floor bedrooms feel undercooled.
Every multiplier and every BTU of internal gain is listed, so you can argue the number with a dealer.
Reports spare capacity, because an oversized AC short-cycles and leaves the room cold but clammy.
Usually yes for a shaded 144 sq ft bedroom on a middle floor, but not on the top floor. At the base rate of about 80 BTU/hr per sq ft, 144 sq ft needs roughly 11,500 BTU/hr, which is just under 1 ton — add the 15% roof uplift for a top-floor room and it crosses 13,000 BTU/hr, which needs a 1.5 ton unit.
About 225 sq ft at base conditions. A 1.5 ton unit delivers 18,000 BTU/hr, and at roughly 80 BTU/hr per sq ft that covers around 225 sq ft with a 10 ft ceiling, average sun and no exposed roof. Coverage drops to about 170-190 sq ft on a top floor or with a long west-facing window.
Yes — plan on roughly 15% more capacity if an uninsulated RCC roof sits directly above the room and is exposed to the sun. The slab absorbs heat all afternoon and re-radiates it into the room well after sunset, which is why top-floor bedrooms stay warm at night.
Yes, beyond about 25% headroom. An oversized unit cools the air fast, hits the setpoint and switches off before it has run long enough to condense moisture out of the room, leaving a cold but humid feel, and the frequent starts wear the compressor. Sizing close to the calculated load, then choosing an inverter model to handle part-load, works better.
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