Field calculator
Cooling tons calculator (BTU to tons)
Cooling equipment is rated in tons, and converting a load between BTU per hour and tons is one of the most common quick checks in the field. The conversion is tons = BTU per hour divided by 12,000, because one ton of refrigeration equals 12,000 BTU per hour, the rate of heat removal to melt one ton of ice over a day. Enter the cooling load in BTU per hour to get the tonnage and the equivalent thermal kilowatts; to go the other way, multiply tons by 12,000 to get BTU per hour. One thing to keep straight: this is a unit conversion of a load you already know, not a load calculation, so the BTU per hour figure should come from a proper Manual J or block load study rather than a rough rule of thumb per square foot, which oversizes equipment and hurts comfort and humidity control. Keep the thermal tonnage separate from the electrical kilowatts the compressor and fans actually draw, which depend on the equipment efficiency, and select and size the equipment with the manufacturer performance data and the engineer.
Result
Cooling tons from BTU per hour: tons = BTU/hr divided by 12,000, because one ton of refrigeration equals 12,000 BTU/hr (the heat to melt one ton of ice in a day). Enter the cooling load in BTU/hr to get the tonnage and the equivalent thermal kilowatts; to go the other way, multiply tons by 12,000 for BTU/hr. This is a unit conversion of a load you already know, not a load calculation, so the BTU/hr figure should come from a proper Manual J or block load, not a rule of thumb per square foot. Keep the thermal tonnage separate from the electrical kilowatts the compressor and fans actually draw, which depend on the equipment efficiency. Size and select equipment with the manufacturer data and the engineer.
Worked example
A rooftop unit shows a 60,000 BTU/h cooling load. How many tons is that?
- Cooling load60,000 BTU/h
- Tons = BTU/h ÷ 12,000 = 60,000 ÷ 12,000 = 5.0 tons.
- In kilowatts: 60,000 ÷ 3,412 = 17.6 kW of cooling.
60,000 BTU/h = 5.0 tons (17.6 kW). One ton of cooling is 12,000 BTU/h by definition.
anvilfield.com/calculators/cooling-tons-btu-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Tons to BTU FAQ
What is a Manual J load calculation?
It is ACCA's room-by-room accounting of a home's heat gain and loss, used to size heating and cooling equipment from the building itself. It tallies the envelope, the windows by orientation, infiltration, ventilation, and the people and appliances inside, then splits the result into sensible and latent load for equipment selection.
Why is oversizing an AC bad?
An oversized AC cools the air fast and shuts off before it runs long enough to remove moisture, leaving the house cold and clammy above comfortable humidity. The short cycling also wastes energy and wears the compressor early, because the start is the least efficient part of every cycle. Right-sizing fixes all of it.
What design temperature do you use for a load calc?
Use the 1 percent cooling and 99 percent heating design conditions from ASHRAE, tabulated in Manual J, not the record high or low. The 1 percent dry-bulb is exceeded only about 88 hours a year. Sizing to the once-a-decade extreme oversizes the equipment for the thousands of normal hours.
What is the difference between sensible and latent load?
Sensible load is heat that changes air temperature, what a thermometer reads. Latent load is the heat in moisture, the energy to condense water vapor out of the air. Manual J figures them separately because equipment removes them separately. A high-sensible unit on a humid house cools but never dries it, which is the usual humidity complaint.
How many square feet per ton should I use to size an AC?
None as a sizing method. The square-feet-per-ton habit, often quoted around 400 to 600 square feet per ton, ignores the windows, insulation, orientation, and air leakage that actually set the load, and it almost always oversizes. Run a Manual J. Use a per-ton figure only as a rough sanity check against the calculated answer.