This free HVAC unit converter translates cooling and heating capacity between BTU/hr, tons of refrigeration, kilowatts (kW), MBH (thousands of BTU/hr), and kcal/hr. Enter a value in any unit and the equivalents update instantly. It's built for HVAC load calculations, equipment selection, and comparing manufacturer ratings that use different unit systems.
All HVAC capacity units measure a rate of heat transfer. The anchors are:
• 1 ton of refrigeration = 12,000 BTU/hr = 3.517 kW = 12 MBH ≈ 3024 kcal/hr • 1 kW = 3412 BTU/hr = 0.2843 tons • 1 MBH = 1000 BTU/hr
"Tons" comes from the cooling effect of melting one ton of ice in 24 hours. MBH (the "M" is the Roman numeral for thousand) is common on US equipment schedules.
Type a number into the unit you know — BTU/hr, tons, kW, MBH, or kcal/hr — and read the converted values in the other fields. Use it to convert a Manual J load result (often in BTU/hr) into tons for equipment selection, to compare a metric chiller rated in kW against a US unit rated in tons, or to translate boiler output in MBH to kW.
A typical residential central AC system is 1.5–5 tons (18,000–60,000 BTU/hr). Light-commercial rooftop units commonly run 3–25 tons. Capacity should come from a proper load calculation (ACCA Manual J for residential, ASHRAE methods for commercial) — never from floor-area rules of thumb alone, which can oversize equipment, hurt dehumidification, and shorten compressor life.
A ton of refrigeration is a unit of cooling capacity equal to 12,000 BTU/hr (3.517 kW). It originally represented the rate of cooling produced by melting one short ton (2000 lb) of ice over 24 hours. It is the standard way US HVAC equipment cooling capacity is rated.
Divide BTU/hr by 3412 to get kW (1 kW = 3412 BTU/hr). For example, a 24,000 BTU/hr (2-ton) system is 24,000 / 3412 ≈ 7.03 kW of thermal capacity. The converter does this automatically across all units.
MBH means thousands of BTU per hour — the "M" is the Roman numeral for 1000. So 60 MBH = 60,000 BTU/hr = 5 tons. MBH is frequently used on US mechanical equipment schedules and boiler ratings.
Area-based rules of thumb (often quoted as ~400–600 sq ft per ton) are only rough screening estimates and frequently oversize equipment. Actual capacity depends on insulation, windows, orientation, climate, occupancy, and internal loads. Always size from a proper load calculation (ACCA Manual J or an ASHRAE method) rather than square footage alone.