BTU to Ton Conversion: HVAC Sizing Made Simple
Why Is 1 Ton = 12,000 BTU/h?
The "ton" in HVAC comes from the ice industry. Before mechanical refrigeration, buildings were cooled with blocks of ice. One ton of cooling capacity equals the heat absorbed by melting one short ton (2,000 pounds) of ice in 24 hours:
2,000 lbs × 144 BTU/lb (latent heat of fusion) ÷ 24 hours = 12,000 BTU/h
This unit stuck in the HVAC industry. Today, when someone says "a 3-ton air conditioner," they mean it can remove 36,000 BTU of heat per hour — equivalent to melting 3 tons of ice daily.
BTU to Ton Conversion Table
| BTU/h | Tons | kW | Typical Application |
|---|---|---|---|
| 6,000 | 0.5 | 1.76 | Small bedroom, home office |
| 9,000 | 0.75 | 2.64 | Master bedroom, small living room |
| 12,000 | 1.0 | 3.52 | Living room, studio apartment |
| 18,000 | 1.5 | 5.27 | Large room, small apartment |
| 24,000 | 2.0 | 7.03 | Small house (800–1,000 sq ft) |
| 30,000 | 2.5 | 8.79 | Medium house (1,000–1,400 sq ft) |
| 36,000 | 3.0 | 10.55 | Standard house (1,400–1,800 sq ft) |
| 48,000 | 4.0 | 14.07 | Large house (1,800–2,500 sq ft) |
| 60,000 | 5.0 | 17.59 | Large house (2,500–3,500 sq ft) |
Conversion Formulas
BTU to Tons
Tons = BTU/h ÷ 12,000
Example: 48,000 BTU/h ÷ 12,000 = 4 tons
Tons to BTU
BTU/h = Tons × 12,000
Example: 2.5 tons × 12,000 = 30,000 BTU/h
BTU to kW
kW = BTU/h ÷ 3,412
Example: 36,000 BTU/h ÷ 3,412 = 10.55 kW
Tons to kW
kW = Tons × 3.517
Example: 3 tons × 3.517 = 10.55 kW
kW to BTU
BTU/h = kW × 3,412
Example: 5 kW × 3,412 = 17,060 BTU/h
Cooling Capacity vs Power Consumption
A common confusion: the "tonnage" or "BTU" rating is the cooling capacity (heat removed), not the electrical power consumed. The ratio between them is the Energy Efficiency Ratio (EER) or Seasonal EER (SEER):
Electrical Power (W) = Cooling Capacity (BTU/h) ÷ SEER
| AC Size | Cooling Capacity | SEER 14 (watts) | SEER 20 (watts) | SEER 25 (watts) |
|---|---|---|---|---|
| 1 ton | 12,000 BTU/h | 857 W | 600 W | 480 W |
| 2 ton | 24,000 BTU/h | 1,714 W | 1,200 W | 960 W |
| 3 ton | 36,000 BTU/h | 2,571 W | 1,800 W | 1,440 W |
| 4 ton | 48,000 BTU/h | 3,429 W | 2,400 W | 1,920 W |
| 5 ton | 60,000 BTU/h | 4,286 W | 3,000 W | 2,400 W |
A SEER 20 unit uses 40% less electricity than a SEER 14 unit for the same cooling output. See our SEER rating guide for details.
Common Mistakes
- Confusing BTU with BTU/h: Equipment ratings are in BTU/h (power), not BTU (energy). The "/" is often dropped in casual usage
- Mixing cooling tons with metric tons: 1 cooling ton = 12,000 BTU/h = 3.517 kW. 1 metric ton = 1,000 kg. They're completely different units
- Assuming more tons = better: Oversizing wastes energy and reduces comfort. Size within 10–15% of calculated load
- Ignoring efficiency: A 3-ton SEER 25 unit costs 40% less to run than a 3-ton SEER 14 unit. Higher upfront cost, lower operating cost
Standards Reference
- ASHRAE Standard 16 — Method of Testing for Rating Room Air Conditioners
- AHRI Standard 210/240 — Performance Rating of Unitary Air-Conditioning & Heat Pump Equipment
- US DOE SEER2 Standards (2023) — Minimum efficiency requirements
Frequently Asked Questions
How many BTU is 1 ton?
1 ton of cooling = 12,000 BTU/h. This comes from the heat needed to melt 1 ton (2,000 lbs) of ice in 24 hours: 2,000 lbs × 144 BTU/lb ÷ 24 hours = 12,000 BTU/h.
How do you convert BTU to tons?
Divide the BTU/h value by 12,000. Tons = BTU/h ÷ 12,000. Example: 36,000 BTU/h ÷ 12,000 = 3 tons.
How many kW is 1 ton of cooling?
1 ton of cooling = 3.517 kW. To convert: kW = Tons × 3.517. Note: this is the cooling capacity, not electrical consumption — a 1-ton AC typically consumes only 0.8–1.5 kW of electricity.
What size AC tonnage do I need?
A general rule: 1 ton per 400–600 sq ft in moderate climates, or 1 ton per 300–400 sq ft in hot climates. For a 1,500 sq ft home: 2.5–3.75 tons. Use our AC size calculator for precise sizing.
Is a higher ton AC better?
Not necessarily. Oversized AC units short-cycle, wasting energy and reducing dehumidification. The right size is within 10–15% of your calculated cooling load.