Methodology
Every result on this site comes from one calculation engine. This page lists its constants, formulas, sources and rounding rules.
Constants
| Quantity | Value |
|---|---|
| 1 refrigeration ton | 12,000 BTU/hrExact. The US refrigeration ton. |
| 1 BTU | 1,055.05585262 JInternational Table BTU (BTU_IT). |
| 1 BTU/hr | 0.2930710701722222 WFrom the BTU_IT, divided by 3,600 seconds. |
| 1 horsepower | 745.6998715822702 WMechanical horsepower (550 ft·lbf/s). Used only on the horsepower pages. |
| 1 refrigeration ton | 3.516853 cooling kWDerived from the rows above; rounded to 6 decimal places. |
“Ton” always means the US refrigeration ton: a rate of heat removal, never weight or refrigerant charge.
Formulas
Every input is first converted to BTU/hr. Results are then calculated from that value:
- Tons = BTU/hr ÷ 12,000
- BTU/hr = tons × 12,000
- Cooling kW = BTU/hr × 0.2930710701722222 ÷ 1,000
Input units
How each input unit becomes BTU/hr:
| Unit | To BTU/hr |
|---|---|
| BTU/hr | No change |
| refrigeration tons | × 12,000 |
| cooling kW | × 1,000 ÷ 0.2930710701722222 |
| cooling W | ÷ 0.2930710701722222 |
| MBH (kBTU/hr) | × 1,000 |
| MMBTU/hr | × 1,000,000 |
| BTU/min | × 60 |
| BTU/s | × 3,600 |
| horsepower | × 745.6998715822702 ÷ 0.2930710701722222 |
Cooling kW and cooling W are cooling capacity, not the electricity the AC uses.
Sources
- NIST SI conversion factors (Special Publication 811, Appendix B.8). International Table BTU and refrigeration-ton conversion basis.
AC size names
ACs are sold by nominal size, and the rated capacity on a spec sheet can sit a little above or below it. To name the size of an AC you already have, this site uses its own documented convention:
- A value within 10% of a nominal size gets that size's name.
- If two sizes are that close, the closer one wins; an exact tie reads “between”.
- A value between two sizes but not close to either reads “between” too.
- Outside the list, only the exact tons show.
Nominal sizes: 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5 tons.
A size name describes an AC; it isn't a recommendation for your space.
Rounding and limits
- Calculations keep full precision; only the display rounds.
- Choose 2, 4 or 6 decimal places (4 by default). Whole numbers drop trailing zeros, so 2 tons shows as “2”.
- A value too small to show reads “less than” the smallest step, such as “less than 0.0001” at 4 decimal places, never zero.
- CSV downloads keep up to 12 significant digits.
- Inputs from 0 to 1,000,000,000,000 in the chosen unit are accepted. Negative numbers, scientific notation and decimal commas are rejected with a message.
Version
Calculation engine version 1.1.0.