BTU vs frigories: what is the difference?
They measure the same thing on different scales: 1 frigorie is 3.97 BTU.
They measure the same thing (cooling capacity) on different scales. 1 frigorie/h = 3.968 BTU/h and 1 BTU/h = 0.252 frigories/h. A 3,000-frigorie unit is 11,905 BTU/h.
Conversion table
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| Frigories/h | BTU/h | kW | Sold as |
|---|---|---|---|
| 1,500 | 5,952 | 1.74 | 6,000 BTU |
| 2,250 | 8,929 | 2.62 | 9,000 BTU |
| 3,000 | 11,905 | 3.49 | 12,000 BTU |
| 4,500 | 17,857 | 5.23 | 18,000 BTU |
| 6,000 | 23,810 | 6.98 | 24,000 BTU |
Where each unit comes from
The frigorie is the negative twin of the kilocalorie: the energy you must remove to cool one kilogram of water by one degree Celsius. It belongs to the traditional metric system and equals exactly 1.163 W when expressed per hour.
The BTU belongs to the imperial system: the energy to raise one pound of water by one degree Fahrenheit. Per hour it equals 0.29307107 W.
Neither is an SI unit. The technically correct one is the watt, and European data sheets do quote capacity in kW.
Why both survive
Commercial habit. In Spain and much of Latin America air conditioners have always been sold in frigories; in English-speaking markets, in BTU and tons. The same manufacturer labels the same machine differently depending on where it is sold.
Why this matters to English speakers
If you are buying or renting in Spain, Argentina, Mexico or Chile, the spec sheet will quote frigories. Knowing that a "3,000 frigorias" split is a 12,000 BTU one-ton unit saves a lot of confusion at the shop.
Mental conversions
- Frigories to BTU: multiply by 4 and take off 1 %. 3,000 → 12,000 → 11,900 BTU.
- BTU to frigories: divide by 4 and add 1 %. 9,000 BTU → 2,250 → 2,270 frigories.
- kW to frigories: multiply by 860.
Neither measures consumption
Neither BTU nor frigories say anything about the electricity the unit uses. Both measure cooling produced. Consumption depends on efficiency, and you need the EER, the SEER or the rated input power to know it.
Sources and methodology
Conversions use exact constants: 1 BTU/h = 0.29307107 W and 1 frigorie/h = 1 kcal/h = 1.163 W. The component sizing model (load per volume by insulation level, 120 W per person, solar gain by glazed area) is set out in full on the air conditioner size calculator. It is a guideline estimate: a professional heat-load calculation considers considerably more variables.
Frequently asked questions
How many frigories is 12,000 BTU?
3,024 frigories/h. Such units are sold as 3,000-frigorie models, less than 1 % apart.
How many BTU is 3,000 frigories?
11,905 BTU/h, commercially rounded to 12,000.
Which unit is better?
Neither: they measure the same thing. The technically correct unit is the watt, and European data sheets quote capacity in kW.
Is a frigorie a negative calorie?
That is the colloquial explanation. Technically a frigorie per hour is one kilocalorie per hour of cooling output.
Do BTU measure electricity use?
No. They measure cooling capacity. Consumption follows from the efficiency rating or the rated power input.