BTU ↔ Ton ↔ kW Converter
BTU/hr, tons, kW — three-way HVAC unit converter.
How to use
Type a value in any one field — the other two update instantly. All three units are linked by the standard refrigeration-ton definition.
- Enter a value in BTU/hr, Tons, or kW — any one input drives the other two.
- Use BTU/hr for furnace and air-conditioner ratings as commonly quoted in North America.
- Use Tons for residential cooling capacity (1 ton = 12,000 BTU/hr).
- Use kW for European heat-pump ratings and electrical equivalence.
Reviewed 3 June 2026 · methodology cited
About this converter
HVAC professionals work in three different unit systems. North American residential and light-commercial equipment is rated in BTU per hour (heating) or tons (cooling). Industrial and European systems are rated in kilowatts. A heat pump quoted as "3 ton" in the US is the same equipment as a "10.5 kW" unit in Europe.
This converter lets you type a value in any one field and the other two recompute live. The reference table below lists the standard residential cooling sizes (1.0 ton through 5.0 ton) in all three units so you can cross-check a manufacturer spec sheet at a glance.
The conversion factors
The ton of refrigeration is defined as the rate of heat removal needed to freeze one short ton (2,000 lb) of water at 0 °C into ice at 0 °C over 24 hours. Numerically: 1 ton = 12,000 BTU/hr = 3.516 852 5 kW. From those, the other conversions follow: 1 BTU/hr = 0.000 293 071 kW; 1 kW = 3,412.142 BTU/hr; 1 kW = 0.284 345 tons.
This is the cooling (refrigeration) ton, not the heating equivalent or the obsolete "ton of coal." The figures are exact by definition — there is no ambiguity in the conversion. When manufacturers list capacity at multiple operating conditions (95 °F outdoor, 80 °F indoor wet bulb for AHRI ratings), they all reduce to the same ton/BTU/kW relationship.
Common cooling sizes
| Tons | BTU/hr | kW | Typical use |
|---|---|---|---|
| 1.0 | 12,000 | 3.52 | 600–1,000 sq ft (small condo, 1 BR apt.) |
| 1.5 | 18,000 | 5.28 | 1,000–1,400 sq ft (2 BR apt., small home) |
| 2.0 | 24,000 | 7.03 | 1,400–1,800 sq ft (typical 3 BR townhouse) |
| 2.5 | 30,000 | 8.79 | 1,800–2,200 sq ft (mid-size single family) |
| 3.0 | 36,000 | 10.55 | 2,200–2,600 sq ft (larger single family) |
| 3.5 | 42,000 | 12.31 | 2,600–3,000 sq ft (large home, two storey) |
| 4.0 | 48,000 | 14.07 | 3,000–3,400 sq ft (large home) |
| 5.0 | 60,000 | 17.58 | 3,400–4,200 sq ft (very large or commercial) |
Sizing notes for residential cooling
Rule-of-thumb sizing for residential air conditioning runs roughly 20 BTU/hr per square foot of conditioned space, but rule-of-thumb is no substitute for a Manual J load calculation by a qualified HVAC contractor. A bigger unit is not better — oversized AC short-cycles, removes less humidity, and costs more to run.
Heat pumps in cold climates (zone 5 and colder) need careful sizing because their output drops as outdoor temperature falls. A 3-ton unit at 47 °F may be a 2-ton unit at 17 °F. Manufacturers publish capacity tables at multiple ambient temperatures — always size the heat pump for your design heating day, not the rated AHRI condition. Backup heat (electric resistance or fossil-fuel) handles the gap on the coldest days.
Frequently asked questions
Why is one ton of cooling 12,000 BTU/hr?
It comes from the latent heat of fusion of water: melting one short ton (2,000 lb) of ice at 0 °C absorbs 288,000 BTU. Spread over 24 hours that is 12,000 BTU per hour — the original "ton of refrigeration" rating that ice-house engineers used in the 1800s. The number became the industry standard and has not changed since.
Is the "ton" the same for heating and cooling?
Numerically yes — 1 ton = 12,000 BTU/hr whether the unit is moving heat in or out. In practice, heating equipment is usually rated directly in BTU/hr (furnaces) or kW (heat pumps), and "tons" is most often used for cooling capacity.
Why is the kW value smaller than the BTU value?
They measure the same power in different unit sizes. One kW equals 3,412 BTU/hr — the BTU is a much smaller unit of energy, so it takes more of them per hour to add up to the same rate. The same 3-ton AC is 36,000 BTU/hr and 10.55 kW.
Should I trust the 20 BTU per square foot rule of thumb?
It is a starting point, not a final answer. Real sizing depends on insulation level, window area and orientation, ceiling height, climate zone, occupancy, internal heat gain, and ductwork. A proper Manual J calculation by an HVAC contractor will often land 15–25 percent below the rule-of-thumb number — and the contractor will pick equipment whose part-load efficiency matches your actual load profile.
Why does heat-pump capacity drop in cold weather?
Heat pumps move heat from outside to inside; as the outdoor air gets colder, the temperature difference grows and the pump works harder to move the same amount of heat. Output capacity drops and the coefficient of performance falls. By design temperature (the coldest typical day for your climate), a heat pump may deliver only half its 47 °F rated capacity — which is why a properly-sized installation includes backup heat for the coldest hours.
Can I size a heat pump myself with this converter?
No. This is a unit-conversion utility — it tells you that 36,000 BTU/hr equals 3 tons equals 10.55 kW, but it does not calculate your home's heating or cooling load. That requires a Manual J / Manual S analysis by a licensed HVAC contractor familiar with your local climate and equipment options.