HVAC Tonnage Calculator — Free Online Calculator
This HVAC tonnage calculator converts cooling capacity between BTU and tons in both directions, and estimates the air-conditioner tonnage a space needs based on its square footage. Use it to size a system, decode a unit's tonnage, or sanity-check a contractor's quote in seconds.
Need a full cooling load instead? This page focuses on converting and sizing in tons. To factor in sun, insulation, ceiling height, and occupancy, use the HVAC BTU Calculator.
Convert BTU ⟷ Tons
Type in either box — the other updates instantly.
Result
24,000 BTU/hr = 2 tons
Estimate tonnage by square footage
A quick starting size using the 20 BTU/sq ft rule.
30,000 BTU/hr
2.5-ton system
AC tonnage by square footage (quick reference)
Based on the 20 BTU/sq ft rule with 8-ft ceilings in a moderate climate. Treat these as starting points, not final sizes.
| Area (sq ft) | Approx. cooling load | System size |
|---|---|---|
| Up to 600 | 12,000 BTU | 1 ton |
| 600 – 900 | 18,000 BTU | 1.5 tons |
| 900 – 1,200 | 24,000 BTU | 2 tons |
| 1,200 – 1,500 | 30,000 BTU | 2.5 tons |
| 1,500 – 1,800 | 36,000 BTU | 3 tons |
| 1,800 – 2,100 | 42,000 BTU | 3.5 tons |
| 2,100 – 2,400 | 48,000 BTU | 4 tons |
| 2,400 – 3,000 | 60,000 BTU | 5 tons |
Figures shown are planning estimates. Confirm final sizing with a full ACCA Manual J load calculation before purchasing or installing equipment.
The formula, explained in plain English
HVAC "tonnage" has nothing to do with weight — it's a measure of cooling power. The whole calculation rests on one fixed conversion plus a simple square-footage rule of thumb.
Why 12,000 BTU = 1 ton?
It dates back to ice cooling: one ton of AC removes the same heat as melting one ton of ice over 24 hours — about 12,000 BTU per hour.
The square-footage rule
Roughly 20 BTU per square foot — about one ton per 500–600 sq ft — gives a fast first estimate for an average home.
Why round up?
Systems are sold in half-ton steps (1.5, 2, 2.5…). Rounding up to the nearest standard size avoids undersizing, though a contractor may fine-tune.
Reading a model number
Outdoor-unit model numbers embed the capacity: a code like 036 means 36,000 BTU. Divide by 12,000 for tons (036 → 3 tons).
Worked examples
Three of the most common tonnage questions, solved step by step.
"My quote says 36,000 BTU — how many tons is that?"
= 3 tons
Answer: a 36,000 BTU system is a 3-ton unit — a typical size for a 1,500–1,800 sq ft home.
"I have a 2.5-ton system — what's its BTU rating?"
= 30,000 BTU/hr
Answer: 30,000 BTU/hr. On the data plate, look for the code 030 in the model number.
"What tonnage for a 1,600 sq ft home in a warm climate?"
35,200 ÷ 12,000 = 2.93 tons
round up → 3-ton system
Answer: about 2.9 tons of load, so a 3-ton system is the right install size. For a precise number, run the full BTU load calculation.
Frequently asked questions
Common questions about AC tonnage and BTU conversion.
How many tons of AC do I need per square foot?
A common rule of thumb is one ton for every 500–600 square feet, which comes from the 20 BTU/sq ft guideline (12,000 BTU = one ton). A 1,500 sq ft home usually needs about 2.5–3 tons, before adjusting for climate, sun, and insulation.
How many BTU is a 2-ton or 3-ton AC unit?
Since one ton equals 12,000 BTU/hr, a 2-ton unit is 24,000 BTU and a 3-ton unit is 36,000 BTU. To convert any tonnage to BTU, multiply by 12,000; to go from BTU to tons, divide by 12,000.
What does "tonnage" mean in HVAC?
Tonnage measures an air conditioner's cooling capacity, not its weight. One ton equals 12,000 BTU/hr — the heat needed to melt one ton of ice in 24 hours. Residential systems typically range from 1.5 to 5 tons.
How do I find the tonnage of my existing AC unit?
Check the model number on the outdoor unit's data plate and look for a 2–3 digit number such as 018, 024, 030, 036, 042, 048, or 060. That's the capacity in BTU (036 = 36,000 BTU). Divide by 12,000 for tons — so 036 = 3 tons.
What size AC (in tons) do I need for a 2,000 square foot house?
Using 20 BTU/sq ft, 2,000 sq ft is about 40,000 BTU, or roughly 3.5 tons, as a starting point. The exact size depends on climate, sun, insulation, and ceiling height, which can move it between 3 and 4 tons.
Can I size my air conditioner by square footage alone?
Square footage gives a solid starting estimate, but it isn't a substitute for a full ACCA Manual J load calculation. Manual J also accounts for windows, orientation, insulation, duct losses, and air infiltration, and is required for permits and equipment warranties.
Is a higher-tonnage air conditioner always better?
No. An oversized unit cools quickly but short-cycles, so it never runs long enough to remove humidity — wasting energy and shortening compressor life. Matching tonnage to the actual load gives the best comfort, efficiency, and lifespan.
How do I determine the AC tonnage I need?
Start with square footage: divide it by 500–600 to estimate tons, or multiply by 20 BTU and divide by 12,000. A 1,800 sq ft home works out to roughly 3 tons. For a precise number, estimate the full cooling load — climate, sun, insulation, and ceiling height — with the BTU Calculator, then convert it to tonnage here.
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