Who this is for: For homeowners comparing quotes that mix units (a '36,000 BTU' system vs a '3-ton') and energy nerds converting to electrical kW for cost math.
Convert either direction between tons, BTU/h and kW — with the common system sizes pre-mapped in a table.
Quick answer: 1 ton = 12,000 BTU/h. Convert tons to BTU by ×12,000 (3 tons = 36,000 BTU), BTU to tons by ÷12,000, and to nominal heat-movement kW by ×3.517. Standard residential sizes: 1.5, 2, 2.5, 3, 3.5, 4, 5 tons.
tons
Tons
3
nominal equipment size
BTU / hour
36,000
cooling delivered
Heat moved
10.55 kW
≈ 1 kW electric per ton consumed
Tons
BTU/h
Heat moved
1.5
18,000
5.3 kW
2
24,000
7.0 kW
2.5
30,000
8.8 kW
3
36,000
10.6 kW
3.5
42,000
12.3 kW
4
48,000
14.1 kW
5
60,000
17.6 kW
1 ton = 12,000 BTU/h (one ton of ice melting over 24 h). kW here is heat moved (×3.517/ton) — a real system draws roughly 1 kW of electricity per ton.
Core facts
Core ratio
1 ton = 12,000 BTU/h
Heat-movement kW
1 ton = 3.517 kW (COP 1 basis)
Electric draw
≈ 0.9–1.2 kW per ton at modern SEER
Standard sizes
1.5 · 2 · 2.5 · 3 · 3.5 · 4 · 5 tons
Example
2.5 tons = 30,000 BTU/h = 8.8 kW moved
Status
Definitions per industry standard. Compiled September 2026.
What is a ton of air conditioning?
A 'ton' is a 19th-century ice-trading unit: the cooling you get from one ton of ice melting over 24 hours, standardized to 12,000 BTU per hour — and that's still the definition HVAC uses. Convert with ×/÷ 12,000 (tons ↔ BTU/h); electrical equivalents divide by the COP, so the nominal figure is 3.517 kW of heat moved per ton (at COP 1) — a real 3-ton unit draws roughly 3–4 kW of electricity because it moves more heat than it consumes. The converter handles both directions and the table below maps the standard equipment sizes: 1.5, 2, 2.5, 3, 3.5, 4 and 5 tons, the only sizes most residential systems ship in.
Common uses
Comparing a quote written in BTU against equipment sold in tons
Converting nameplate BTU to tons for a Manual J cross-check
Estimating electrical draw (kW) before running cost math
Checking a heat pump's heating rating against its cooling tonnage
Frequently Asked Questions
How many BTU is one ton?
Exactly 12,000 BTU per hour. The unit comes from melting one short ton (2,000 lb) of ice over 24 hours: 2,000 × 144 BTU/lb ÷ 24 h = 12,000 BTU/h. Modern refrigeration kept the unit.
How many kW is a 3-ton AC?
It moves 3 × 3.517 ≈ 10.5 kW of heat, but consumes roughly 3–4 kW of electricity at a typical SEER — that ratio (heat moved ÷ electricity used) is the whole point of the SEER/EER ratings. Convert carefully: kW of cooling ≠ kW consumed.
Why do systems come in half-ton steps?
Compressors and coils are manufactured at 1.5, 2, 2.5, 3, 3.5, 4 and 5 tons (modulating units fill the gaps). Load calculations land between steps, so you snap up to the next size — but as close as possible, for the dehumidification reasons above.
Is a bigger tonnage ever the right call?
Between two sizes, take the one at or just above your calculated load. Buying two sizes up for 'safety' costs you humidity control, cycling life and money. The load calculator, not the converter, makes that call.
Does this work for heat pumps?
The ton ↔ BTU math is identical for heating and cooling ratings. Check both numbers on a heat pump's spec sheet — heating capacity at 17°F/5°F drops below the cooling tonnage, and that deficit decides backup heat.