Air Conditioner Tonnage Calculator
Air conditioner capacity is measured in tons, where one ton equals exactly 12,000 BTU per hour. This calculator does two things. First, it converts a known cooling load in BTU per hour into tons, an exact definitional conversion. Second, it offers a quick area-based estimate: enter your floor area and a cooling factor in BTU per square foot, and it estimates the load and the tonnage. The area estimate is a screening figure only. For real equipment selection, an ACCA Manual J load calculation is the correct method, since it accounts for insulation, windows, and climate.
Tonnage formula
Tonnage = cooling load (BTU/hr) / 12,000
Area estimate (BTU/hr) = floor area * cooling factor
Area estimate (tons) = area estimate (BTU/hr) / 12,000
One ton equals exactly 12,000 BTU per hour, so the BTU-to-tons conversion is exact. The area estimate uses a cooling factor you set; treat it as a quick screen rather than a design figure.
Notes on tonnage
- The 12,000 BTU per hour per ton conversion is a fixed definition, not an approximation.
- Residential systems are commonly sold in half-ton steps, so round to the nearest available size.
- Do not oversize: an oversized unit short cycles and leaves humidity behind.
- The cooling factor is yours to set based on climate, insulation, and windows.
- For equipment selection, rely on an ACCA Manual J load calculation, not this screen.
AC tonnage: frequently asked questions
What is a ton of air conditioning?
One ton of cooling equals 12,000 BTU per hour. The term comes from the cooling effect of melting one ton of ice over 24 hours. To convert a cooling load in BTU per hour to tons, divide by 12,000; to convert tons to BTU per hour, multiply by 12,000.
How many tons of AC do I need?
Tonnage depends on your cooling load, which is driven by area, climate, insulation, windows, and internal gains. A rough screen multiplies floor area by a cooling factor in BTU per square foot, then divides by 12,000. For accurate sizing, use an ACCA Manual J load calculation.
How do I convert BTU to tons?
Divide the BTU per hour figure by 12,000. For example, 24,000 BTU per hour is 24,000 / 12,000 = 2 tons. Conversely, a 3-ton system delivers 3 x 12,000 = 36,000 BTU per hour. This is an exact definitional conversion, not an estimate.
Is bigger always better for an air conditioner?
No. An oversized system cools quickly but cycles off before it removes enough humidity, leaving the space cool but damp, and it wears faster from short cycling. The Department of Energy recommends matching capacity to the calculated load for the best comfort and efficiency.
Does the area estimate replace a load calculation?
No. The area-based estimate here is a quick screen using a factor you set. Real sizing must account for insulation, window area and orientation, air leakage, and local design temperatures, which is what ACCA Manual J does. Use this tool to sanity-check, not to specify equipment.
Official sources
- U.S. Department of Energy, central air conditioning: energy.gov.
- Air Conditioning Contractors of America (Manual J load calculation standard): acca.org.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.