Air Conditioner Sizing: BTU/hr vs Tons vs kW
The 'ton' in AC comes from the cooling of one ton of ice melting in 24 hours = 12,000 BTU/hr. It's a real physical unit, not a marketing number.
1 ton AC = 12,000 BTU/hr = 3.517 kW. A '3-ton unit' = 36,000 BTU/hr — sized to about 1500 sq ft. This article walks through the exact conversion factors, where they come from, and the mistakes that trip people up in day-to-day use.
The exact factors
1 ton → 12k BTU/hr (3.517 kW) > 3 ton → 36k BTU/hr (10.55 kW)
Why the numbers matter
Most casual conversions round early and lose precision that only shows up at scale. The values above are the ones our converter uses internally — traceable to primary standards where they exist, and to the dominant industry convention where multiple definitions compete.
Worked example
Take the top row above: 1 ton converts to 12k BTU/hr. In a real-world use case (3.517 kW), the difference between using the rounded shortcut and the precise factor typically shows up at the 2-5% level — enough to matter for anything measured, billed, or dosed, and invisible for anything estimated.
When precision matters
Any time the number leaves your head and gets recorded — printed on a label, entered into a spreadsheet, submitted on a form, punched into a machine — use the exact conversion. Mental shortcuts are fine for feel, not for records.
The five-second recap
Use the exact factors above. Round only in your final display, never mid-calculation. Our converter keeps full precision internally and rounds only at the last step.
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FAQ
What is the exact conversion for 1 ton to 12k BTU/hr?+
1 ton → 12k BTU/hr — see the table above. Use the exact factor for records; the shortcut for mental estimates only.
Why does the shortcut differ from the exact value?+
Shortcuts drop 2-4 significant figures for mental math. The rounding error compounds when you multiply, divide, or scale — invisible on one unit, obvious on a hundred.
Which convention should I use in mixed-unit projects?+
Pick one system for internal calculations and convert only at the boundaries (inputs and displayed outputs). Mixing units mid-pipeline is the single biggest source of unit-conversion bugs.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-10 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.