Actonnage Calculator
Free Actonnage Calculator for home & garden projects. Enter dimensions to get material lists and cost estimates. Get results you can export or share.
Reviewed by Abdullah, Technical Content Specialist
Formula
Tonnage = (Sq Ft x 20 BTU x Climate Factor x Insulation Factor x Height Adj) / 12,000
Start with a base of 20 BTU per square foot, then adjust for your climate zone, insulation quality, and ceiling height. Divide the total BTU requirement by 12,000 to convert to tons of cooling capacity. One ton of refrigeration equals 12,000 BTU per hour. Round up to the nearest standard AC unit size (1.5, 2, 2.5, 3, 3.5, 4, or 5 tons).
Worked Examples
Example 1: Standard Home in Warm Climate
Problem:Size an AC unit for a 1,500 sq ft home with 8 ft ceilings in a warm climate zone with average insulation.
Solution:Base BTU = 1,500 x 20 = 30,000\nClimate multiplier (warm) = 1.15\nInsulation multiplier (average) = 1.0\nTotal BTU = 30,000 x 1.15 = 34,500\nTonnage = 34,500 / 12,000 = 2.88 tons
Result:Recommended: 3-ton AC unit
Example 2: Large Home with High Ceilings
Problem:Size an AC unit for a 2,500 sq ft home with 10 ft ceilings in a hot climate with good insulation.
Solution:Base BTU = 2,500 x 20 = 50,000\nClimate multiplier (hot) = 1.3\nInsulation multiplier (good) = 0.85\nHeight adjustment = 1 + (10-8) x 0.125 = 1.25\nTotal BTU = 50,000 x 1.3 x 0.85 x 1.25 = 69,063\nTonnage = 69,063 / 12,000 = 5.76 tons
Result:Recommended: Two 3-ton units or one 5-ton unit with supplemental cooling
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy