HVAC & BTU Calculators
BTU sizing for air conditioners and mini-splits — find the cooling capacity a room needs and the right unit size.
CalcBooth’s HVAC calculators size cooling to a room. The BTU calculator works out how many BTUs an air conditioner needs from the room area, ceiling height, sun exposure, climate and how the space is used, then suggests a standard unit size. The mini-split sizing calculator does the same and points you to the nearest 9k, 12k, 18k or 24k BTU mini-split. The BTU converter explains what a BTU is and converts between BTU/hr, kilowatts, watts and tons of cooling. These are quick rule-of-thumb estimates to get you in the right range; a contractor’s Manual J load calculation is the precise sizing for a permanent install.
Which calculator do I need?
| Calculator | What it works out |
|---|---|
| BTU Calculator | Find how many BTUs you need to cool a room — enter the size, ceiling height, sun exposure and climate to get the cooling BTUs and a recommended air conditioner size in BTU and tons. |
| Mini Split Sizing Calculator | Find what size mini split you need — enter the room size, ceiling height, sun and climate to get the cooling BTUs and the nearest standard mini-split size (9k, 12k, 18k, 24k BTU). |
| BTU Converter | Understand what a BTU is and convert between BTU per hour, kilowatts, watts and tons of cooling — enter any value to see the equivalents instantly. |
How these estimates are built
Every calculator in this category publishes the formula it runs, the constants it assumes, a worked example you can reproduce by hand, and the standard or manufacturer data sheet each constant comes from. Quantities include an adjustable waste allowance and round up to whole units, because you cannot buy part of a bag or box.
Cost figures are national US ranges and are material-only unless a calculator says "installed", so they exclude tax, permits and local labour rates. These are planning estimates, not quotes — read the full calculation methodology for what they cover, and the disclaimer for the structural and HVAC limits that apply.