BTU to Tons Calculator
Convert air-conditioner cooling capacity between BTU/hr and tons.
Reviewed by the ToolNestr Editorial Team — July 2026
How BTU to tons conversion works
The relationship between BTU per hour and tons of cooling is fixed: one ton of refrigeration equals exactly 12,000 BTU per hour. This standard originates from the days when ice was the primary cooling medium — one ton of ice melting over 24 hours absorbs 288,000 BTU of heat, which works out to 12,000 BTU per hour. To convert BTU/hr to tons, divide by 12,000. To convert tons to BTU/hr, multiply by 12,000.
Kilowatts of cooling can be derived from BTU/hr using the conversion factor 1 BTU/hr = 0.000293071 kW. This is equivalent to multiplying BTU/hr by 0.000293071, or multiplying tons by 3.517 (since 12,000 × 0.000293071 ≈ 3.517). These three units — BTU/hr, tons, and kW — are the most common ways air-conditioner cooling capacity is specified across different regions and manufacturers.
Worked example
Common AC sizes at a glance
Residential air-conditioners typically range from 1 to 5 tons. Here are the most common sizes and their equivalents across all three units.
| Tons | BTU/hr | kW | Typical coverage |
|---|---|---|---|
| 1.0 | 12,000 | 3.52 | 400 – 600 sq ft |
| 1.5 | 18,000 | 5.28 | 600 – 900 sq ft |
| 2.0 | 24,000 | 7.03 | 900 – 1,200 sq ft |
| 2.5 | 30,000 | 8.79 | 1,200 – 1,500 sq ft |
| 3.0 | 36,000 | 10.55 | 1,500 – 1,800 sq ft |
| 4.0 | 48,000 | 14.07 | 1,800 – 2,500 sq ft |
| 5.0 | 60,000 | 17.58 | 2,500 – 3,200 sq ft |
Sizing an AC unit
When shopping for a new air-conditioner, different brands quote capacity in different units. A 2-ton unit from one manufacturer might be listed at 24,000 BTU/hr by another. This calculator helps you compare them directly.
HVAC specifications
HVAC engineers work with BTU/hr for heat load calculations and duct sizing, but specify equipment in tons. Quickly convert between the two without pulling out reference tables.
Comparing quotes
Contractors may quote you in tons while equipment datasheets list BTU/hr. Use the calculator to verify you are comparing the same cooling capacity across different proposals.
International standards
BTU/hr is common in North America, while kW is the preferred unit in Europe and Asia. When specifying equipment for an international project, convert all capacities to a common unit.
Tips for AC capacity conversion
"Ton" means cooling power, not weight
In HVAC, a "ton" refers to the rate of heat removal, not the physical weight of the equipment. One ton of cooling removes 12,000 BTU of heat per hour. A 3-ton air-conditioner does not weigh 3 tons — it removes heat at the same rate as melting 3 tons of ice per day.
Room sizing depends on many factors
The rough rule of 20 BTU per square foot is a starting point, but actual cooling requirements depend on ceiling height, window area and orientation, insulation levels, number of occupants, heat-producing appliances, local climate, and sun exposure. Always get a proper Manual J load calculation before purchasing equipment.
Oversizing is worse than undersizing
An oversized AC unit cools the space quickly but shuts off before removing enough humidity, leaving the room feeling cold and clammy. Short cycling also increases wear on the compressor and reduces efficiency. Proper sizing is critical for both comfort and equipment longevity.
Check the SEER rating too
Cooling capacity (tons/BTU) tells you how much cooling the unit can provide, but SEER (Seasonal Energy Efficiency Ratio) tells you how efficiently it does so. A higher SEER means lower operating costs. Modern minimum standards are 14–15 SEER, with premium units reaching 25+ SEER.
Understanding HVAC cooling units
The British Thermal Unit (BTU) is a measure of heat energy. One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. When applied to air conditioning, BTU per hour (BTU/hr) measures the rate at which heat is removed from a space. This is the most common specification for residential air-conditioners, heat pumps, and furnaces in North America.
The ton of refrigeration
The "ton of refrigeration" is a historical unit that dates back to the ice-harvesting era. The latent heat of fusion of ice is 144 BTU per pound. One short ton (2,000 lb) of ice absorbs 2,000 × 144 = 288,000 BTU of heat as it melts over 24 hours. Dividing by 24 hours gives 12,000 BTU per hour, which became the standard definition of one ton of cooling. Despite being an archaic unit, it remains the standard for specifying residential and light commercial HVAC equipment in the United States and Canada.
Kilowatts in HVAC
In most of the world, cooling capacity is specified in kilowatts (kW). One kW equals 3,412 BTU/hr, so converting the other way: 1 BTU/hr = 0.000293071 kW or approximately 0.293 watts. For a 2-ton (24,000 BTU/hr) unit, the cooling capacity is 24,000 × 0.000293071 = 7.03 kW. Note that this is the thermal cooling output, not the electrical input power. The actual electrical consumption depends on the unit's efficiency (EER or SEER).
Practical applications
HVAC professionals use these conversions daily. When performing heat load calculations, the total cooling load is computed in BTU/hr based on the Manual J methodology. The result is then converted to tons to select the appropriate equipment. Duct sizing uses BTU/hr, refrigerant line sizing uses tons, and electrical design uses kW. Being fluent across all three units is essential for proper system design.
For homeowners, understanding these units helps when comparing quotes from different contractors, reading equipment specification sheets, and discussing options with HVAC professionals. A contractor who offers a "3-ton unit" and another who offers a "36,000 BTU system" are offering the same capacity — knowing the conversion prevents confusion and ensures you receive comparable proposals.
Related tools
How to use the BTU to Tons Calculator
Set direction
Choose whether you want to convert BTU/hr to tons or the reverse. The calculator updates instantly.
Enter the value
Type the cooling capacity in the input field. The tool accepts decimals and works with any value, including zero.
Read all results
Tons, BTU/hr, and kW are shown simultaneously so you have the complete picture without extra steps.
Frequently asked questions
How many BTU is 1 ton?
Exactly 12,000 BTU per hour.
What size AC do I need?
Rough rule ~20 BTU per square foot, but get a proper load calculation for accuracy.
What is a ton in kW?
About 3.52 kW of cooling per ton.
Where does "ton" come from?
It originated from the cooling power of one ton of ice melting per day — a legacy unit still common in HVAC.
Sources & references
This tool uses standard formulas and reference values from:
- • NFPA 70 — National Electrical Code (NEC), conduit fill, box fill and conductor ampacity. nfpa.org
- • IPC-2221, Generic Standard on Printed Board Design (trace width / current). ipc.org
- • NIST reference constants and unit definitions; IEEE standards where applicable. nist.gov
For educational and preliminary use. Verify against full engineering calculations and the governing standard before any real design.