Get a starting BTU and tonnage estimate to size an air conditioner, mini-split or heater for a room.
Cooling load starts from floor area times a climate factor, then adjusts for ceiling height and occupancy. Tonnage is BTU divided by 12,000.
This is a quick sizing guide, not a substitute for a Manual J load calculation. Insulation, windows, kitchens and whole-home systems all shift the number — have an HVAC pro confirm before you buy central equipment.
A common rule of thumb is 20 to 30 BTU per square foot — nearer 20 in cool, shaded rooms and 30 in hot, sunny ones. This calculator uses 25 as an average starting point and lets you adjust for climate.
Divide BTUs by 12,000. So a 24,000 BTU unit is 2 tons, and a 36,000 BTU unit is 3 tons. Tonnage is just the trade\u2019s shorthand for cooling capacity, not the weight of the equipment.
No. An oversized unit short-cycles — it cools fast, shuts off, and never runs long enough to pull humidity out of the air. That leaves the room clammy and wears the compressor. Right-sizing matters more than raw power.
No. For central systems, a Manual J calculation accounts for insulation, window area, orientation and air leakage. Use this figure to sanity-check a quote or size a room mini-split, then confirm with an HVAC contractor.
The Home Renovation Project Manager rolls every calculator into one budget — room by room, with a shopping list, contractor quote comparison and a live over-budget warning.