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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.
This 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.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
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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