Cooling Tonnage Calculator
Convert between BTU/hr and tons of cooling (and thermal kW) to size or compare equipment. This is pure unit conversion — one ton of refrigeration is 12,000 BTU/hr by definition, about 3.517 kW of heat removal — so the answers are exact, not estimates. What it does not tell you is how many tons a building needs: that comes from a load calculation. Free, no login.
Convert
Equivalent
Definition-based conversions: 1 ton of refrigeration = 12,000 BTU/hr ≈ 3.517 kW. Not a code value.
How this calculator works
Three identities, nothing else — this tool converts units; it does not estimate anything:
1 ton = 12,000 BTU/hr (exact by convention) · kW = BTU/hr ÷ 3,412.142 · 1 ton ≈ 3.517 kW
The ton of refrigeration comes from ice: melting a 2,000 lb ton of ice over 24 hours absorbs 12,000 BTU each hour, and the unit stuck. The kW shown is thermal — the rate of heat removal — not the electrical draw; input power is far lower because a vapor-compression machine moves heat rather than generating it (divide BTU/hr by the EER for input watts). Manufacturers encode nominal tonnage in model numbers as thousands of BTU/hr (024 = 2 tons, 036 = 3, 060 = 5); actual delivered capacity at your conditions comes from the AHRI rating and expanded performance data, and required capacity comes from a load calculation — never from a converter.
Worked example
A condenser labeled 036 — nominally 36,000 BTU/hr (the calculator’s default):
- Tons: 36,000 ÷ 12,000 = 3.00 tons.
- Thermal kW: 36,000 ÷ 3,412.142 = 10.55 kW of heat removal.
- Reverse check: 3 tons × 12,000 = 36,000 BTU/hr — the conversion is exact in both directions.
Enter 36,000 BTU/hr above (or flip to Tons → BTU/hr with 3) to reproduce it.
Reference: BTU / tons / kW / airflow, 1–5 tons
The standard equipment sizes tabulated — BTU/hr and thermal kW are exact conversions; the airflow column is the nominal 400 CFM-per-ton rule of thumb with its 350–450 design range (and DX coils should stay above about 300 CFM/ton to avoid freezing):
| Tons | BTU/hr | Thermal kW | Nominal CFM (350–450 range) |
|---|---|---|---|
| 1 | 12,000 | 3.52 | 400 (350–450) |
| 1.5 | 18,000 | 5.28 | 600 (525–675) |
| 2 | 24,000 | 7.03 | 800 (700–900) |
| 2.5 | 30,000 | 8.79 | 1,000 (875–1,125) |
| 3 | 36,000 | 10.55 | 1,200 (1,050–1,350) |
| 3.5 | 42,000 | 12.31 | 1,400 (1,225–1,575) |
| 4 | 48,000 | 14.07 | 1,600 (1,400–1,800) |
| 5 | 60,000 | 17.58 | 2,000 (1,750–2,250) |
Frequently asked questions
How many BTU is a ton of cooling?
One ton of cooling is exactly 12,000 BTU/hr by definition. The term comes from ice: melting one 2,000 lb ton of ice absorbs about 288,000 BTU (144 BTU per pound of ice), and spread over 24 hours that's 12,000 BTU/hr. So a 3-ton condenser is a 36,000 BTU/hr machine — the two are just different units for the same capacity.
Is the kW shown here the electrical power the unit draws?
No — it's thermal. One ton = 12,000 BTU/hr ≈ 3.517 kW of heat removal, which is what this converter reports. Electrical input is much lower because a heat pump moves heat rather than generating it: divide the BTU/hr by the unit's EER to get input watts. A 3-ton unit at EER 12 draws about 36,000 ÷ 12 = 3,000 W at rating conditions, while removing roughly 10.5 kW of heat.
How many square feet does a ton of AC cover?
Rule-of-thumb answers run roughly 400–600 ft² per ton, but the honest answer is "it depends": climate, insulation, glazing, and ceiling height swing the number widely, and older rules like 400 ft²/ton oversize badly on tight modern construction. Treat square-feet-per-ton as an estimate for early budgeting only — an ACCA Manual J load calculation is the authoritative way to size equipment.
How many CFM of airflow per ton of cooling?
Nominal design airflow is 400 CFM per ton. In practice you target about 350 CFM/ton in humid climates (more latent removal — a colder coil wrings out more moisture) and up to 450 CFM/ton in dry climates (more sensible capacity). A 3-ton system should therefore be moving roughly 1,050–1,350 CFM, and verifying that airflow is one of the first steps in any performance diagnosis.
What do the numbers in an AC model number mean?
Most manufacturers encode nominal capacity in thousands of BTU/hr: 018 = 1.5 tons, 024 = 2, 030 = 2.5, 036 = 3, 048 = 4, 060 = 5. That's a nominal size — the actual delivered capacity at your design conditions comes from the AHRI rating and the manufacturer's expanded performance tables, and it changes with outdoor temperature, indoor wet bulb, and airflow. Use this converter to translate the model number, then check the performance data for the real number.
Method: definitional unit conversion — 1 ton of refrigeration = 12,000 BTU/hr (exact by convention), kW at 3,412.142 BTU/hr per kW, so 1 ton ≈ 3.517 kW thermal. Not a code value and not a sizing method: tonnage required comes from an ACCA Manual J or equivalent load calculation, delivered capacity from the AHRI rating and the manufacturer’s expanded performance tables, and airflow per ton (nominally 400 CFM) is a separate rule of thumb with its own caveats.
Pair with the BTU / tonnage / CFM conversion chart for the full table, the CFM per ton chart for the airflow conventions and caveats, the refrigerant line sizing chart for line sizes by tonnage, or the BTU & Heat Load Calculator for a first-pass load to convert.