Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Cooling capacity (tons)
4.25
Cooling load (BTU/hr)
52,000
Suggested furnace output (BTU/hr)
73,000
Airflow needed (CFM)
1,727
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter conditioned area (sq ft).
- 2Enter ceiling height (ft).
- 3Enter climate zone.
- 4Enter sun exposure.
- 5Enter regular occupants.
- 6Read your cooling capacity (tons) on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
Oversized systems short-cycle, never dehumidify properly, and wear out early. This is a screening estimate — a full Manual J load calculation is the real answer before you buy equipment.
Worked example
Using the values the calculator loads with:
Inputs
- Conditioned area: 1800 sq ft
- Ceiling height: 9 ft
- Climate zone: Moderate
- Sun exposure: Average
- Regular occupants: 4
Results
- Cooling capacity (tons): 4.25
- Cooling load (BTU/hr): 52,000
- Suggested furnace output (BTU/hr): 73,000
- Airflow needed (CFM): 1,727
What each field means
Inputs
- Conditioned area (sq ft)
- The conditioned area used in the calculation, measured in sq ft. Starts at 1800 sq ft so you have a working example on load.
- Ceiling height (ft)
- The ceiling height used in the calculation, measured in ft. Starts at 9 ft so you have a working example on load. Accepted range: 7–20 ft.
- Climate zone
- Pick the option that matches your situation — the maths changes per option. Choices: Cool northern, Moderate, Hot southern.
- Sun exposure
- Pick the option that matches your situation — the maths changes per option. Choices: Heavily shaded, Average, Very sunny.
- Regular occupants
- The regular occupants used in the calculation. Starts at 4 so you have a working example on load.
Results
- Cooling capacity (tons)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cooling load (BTU/hr)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Suggested furnace output (BTU/hr)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Airflow needed (CFM)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the hvac sizing calculator work?
Oversized systems short-cycle, never dehumidify properly, and wear out early. This is a screening estimate — a full Manual J load calculation is the real answer before you buy equipment. The underlying maths is: BTU ≈ Area × BTU per sq ft, adjusted for ceiling height, sun exposure, and occupancy. Tons = BTU ÷ 12,000.
What do I need to enter?
5 values: conditioned area, ceiling height, climate zone, sun exposure, and regular occupants. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the cooling capacity (tons) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). HVAC Sizing Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/hvac-sizing
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/hvac-sizing" target="_blank" rel="noopener">HVAC Sizing Calculator — RevenueLab</a> (2026).</p>
Source: [HVAC Sizing Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/hvac-sizing) (2026).