Quick answer: Chiller tonnage (TR) = total building cooling load (BTU/hr) ÷ 12,000. For early sizing, use area-per-ton rules of thumb by occupancy (e.g. offices ~250 sq ft/TR, malls ~150 sq ft/TR), then confirm with a detailed load.
How to size a chiller
TR = Total cooling load (BTU/hr) / 12,000
Rule of thumb (sq ft per TR):
Office 250-300 | Hotel 250 | Hospital 200 | Mall 150
Add diversity across zones; include fresh-air loadWorked example
50,000 sq ft office at 250 sq ft/TR ≈ 200 TR. Split across 2 × 110 TR chillers (N+1 style) for redundancy and part-load efficiency. Verify with a block cooling-load calculation before selection.
Building cooling capacity in TR for any occupancy. Free tool.
Open the Chiller Tonnage Calculator →Frequently Asked Questions
How do you calculate chiller tonnage?
Divide the total building cooling load in BTU/hr by 12,000 to get tons of refrigeration. For quick sizing, use area-per-ton rules of thumb by occupancy, then confirm with a detailed load calculation.
How many square feet per ton for an office?
Roughly 250-300 sq ft per ton for a typical office, less for high-occupancy or high-glass spaces. Malls and restaurants need far fewer sq ft per ton.