HVAC Tonnage Calculator
Convert square footage or BTU/hr into the right AC tonnage. Results round to the nearest 0.5 ton — the increment most residential equipment is sold in.
Inputs
Results
Visualization
See where your load lands on the tonnage scale
Drag any value into the field below to see the equivalent AC tonnage and where it falls relative to standard equipment sizes. Notice how BTU values between two sizes round up — equipment is only sold in 0.5-ton steps.
Live tonnage scale
BTU/hr to AC tonnage
Equipment is sold in 0.5-ton increments. Round to the nearest 0.5 ton — oversizing past that hurts dehumidification more than the rare design day helps.
Formula
The tonnage formula
Converting BTU/hr to AC tonnage is a simple division. Going from square footage requires a climate factor and envelope adjusters.
Round to the nearest 0.5 ton.
Climate factor ≈ 18–35 BTU/sqft depending on IECC zone, insulation, and sun.
Reference
AC tonnage by typical home size
The table below pairs each tonnage tier with the home size it typically serves at average insulation in a temperate climate (IECC zone 4). Hot climates (zone 1–2) push you up one tier; well-insulated modern builds push you down one.
| Tonnage | BTU/hr | Typical home size | CFM |
|---|---|---|---|
| 1.5 tons | 18,000 | 600–900 sq ft | 600 CFM |
| 2 tons | 24,000 | 900–1,200 sq ft | 800 CFM |
| 2.5 tons | 30,000 | 1,200–1,500 sq ft | 1,000 CFM |
| 3 tons | 36,000 | 1,500–1,800 sq ft | 1,200 CFM |
| 3.5 tons | 42,000 | 1,800–2,200 sq ft | 1,400 CFM |
| 4 tons | 48,000 | 2,200–2,700 sq ft | 1,600 CFM |
| 4.5 tons | 54,000 | 2,700–3,200 sq ft | 1,800 CFM |
| 5 tons | 60,000 | 3,200–3,800 sq ft | 2,000 CFM |
Pitfalls
Common tonnage sizing mistakes
- Sizing on square footage alone — ignores climate zone, which can shift the answer by 30%+
- Oversizing 'just to be safe' — short-cycles, doesn't dehumidify, costs more upfront and to run
- Sizing for the worst day instead of the design day — the 99% design temp covers all but ~88 hours per year
- Ignoring the latent cooling load in humid climates — undersized latent capacity = cold but clammy rooms
- Forgetting to match the air handler — a 3-ton condenser needs a 3-ton coil at 1,200 CFM
Tonnage FAQ
Quick answers to common HVAC sizing questions.