How many BTU per square foot?
Most cooled rooms need 20–30 BTU per sq ft depending on insulation, sun exposure, and climate. Hot, sunny, or poorly insulated spaces need more; well-insulated tiny homes often need less.
BTU Calculator
British Thermal Units (BTU) measure how much heat an air conditioner must remove per hour. Enter your room dimensions, insulation, and climate zone — we estimate cooling load and round up to common mini-split sizes.
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Sizing settings
The 20–30 BTU per square foot rule
A quick planning shortcut: multiply room square footage by 20–30 BTU for cooling. A 200 sq ft bedroom at 25 BTU/sq ft needs about 5,000 BTU calculated load — but retail units start at 6,000–9,000 BTU, so you buy the next standard size up.
Our BTU per square foot guide explains when to use the low or high end of that range based on insulation and sun exposure.
What this calculator adjusts for
Ceiling height above 8 ft adds volume. Sunny west-facing walls add load. Each occupant beyond two adds roughly 600 BTU. Kitchen appliances add sensible heat — toggle kitchen load for open living/kitchen spaces.
This is a DIY planning estimate, not a Manual J load calculation. Permits and whole-house central HVAC need a licensed pro.
BTU vs tons vs mini-split packaging
12,000 BTU = 1 ton of cooling. Mini-splits are sold as 9k, 12k, 18k, and 24k BTU heads. Use our tonnage calculator to see both numbers side by side.
Frequently asked questions
How do I convert BTU to tons?
Divide BTU by 12,000. A 12,000 BTU unit is 1 ton. Mini-splits are commonly sold as 9k, 12k, 18k, or 24k BTU single-zone heads.
Is this a substitute for a Manual J load calculation?
No. This tool gives planning estimates for DIY sizing. Licensed HVAC pros use Manual J for final equipment selection and permit work.
Related calculators
HVAC Calculators · https://hvaccalculators.net/btu-calculator/