How to Use the Cooling Tower Sizing Calculator
A cooling tower's required size is based on the heat load its condenser water carries away. Using water's specific heat, Heat Load (BTU/hr) = GPM × 500 × Temperature Range (°F), where 500 is the standard engineering constant for water (8.33 lb/gal × 60 min/hr × 1 BTU/lb·°F). Dividing that by 1 Ton of Refrigeration = 12,000 BTU/hr — the US customary definition — gives the required tower size in tons.
Note that this US ton is a completely different unit than the kcal-based refrigeration ton (1 RT = 3,320 kcal/h) used in Korea and Japan — it isn't a simple unit conversion between the two, so this calculator is built from scratch around GPM and °F rather than converting a metric result. The AHRI standard rating condition for cooling towers is 3 GPM per ton at a 10°F range (95°F entering, 85°F leaving, 78°F wet bulb), which is a common starting point if you don't have exact design values yet.
Keep in mind this result is a theoretical heat load based only on flow and temperature range — actual tower selection also depends on design wet-bulb temperature, site altitude, and safety margin. Use this as a preliminary sizing reference, and confirm final tower selection against manufacturer performance data with a mechanical engineer before purchase or installation.
Frequently Asked Questions
The AHRI standard rating condition for a cooling tower is 3 GPM per ton at a 10°F range (95°F entering, 85°F leaving water, 78°F wet bulb). Many designs use a 10°F range, but your actual system's range may differ, so check your design documents.
This is a theoretical heat load based only on flow rate and temperature range. Actual tower selection also depends on design wet-bulb temperature, altitude, and safety margin, so final selection should be verified against manufacturer performance data with a mechanical engineer.