SettingsSettings for this calculationUS
The length of the room to be cooled.
Measure the floor along one wall.
Tools needed: Tape measure
The width of the room to be cooled.
Measure perpendicular to the length.
Tools needed: Tape measure
Taller ceilings mean more air volume to cool.
A room with a vaulted or very tall ceiling needs meaningfully more cooling capacity than the same floor area with a standard ceiling.
Direct sun through windows adds significant heat load.
A sunroom or a room with large west-facing windows needs more cooling capacity than an equivalent shaded room.
Recommended cooling capacity (BTU/hr)
2,990 BTU/hr
This is a rough planning estimate, not a Manual J load calculation — actual sizing should be verified by an HVAC professional, especially for whole-house systems.
- Room area
- 149.5 sq ft
- Baseline (20 BTU/sq ft)
- 2,990 BTU/hr
- Same capacity in kW
- 0.88 kW
They open the calculator with your figures already in it
BTU Cooling / AC Sizing Calculator: 2,990 BTU/hr — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Rule-of-thumb baseline: approximately 20 BTU per square foot for cooling, within a commonly cited 18-30 BTU/sq ft range depending on insulation, ceiling height, and climate
- A precise sizing should use a full Manual J load calculation performed by an HVAC professional — this tool gives a rough planning estimate only
Inputs used
- Room Length
- 13 ft
- Room Width
- 11.5 ft
- Ceiling Height
- Standard (up to 8 ft / 2.4 m)
- Sun Exposure
- Moderate
Intermediate steps
- Room area
- 149.5 sq ft
- Baseline (20 BTU/sq ft)
- 2,990 BTU/hr
- Same capacity in kW
- 0.88 kW
Confidence note: This is a rough planning estimate, not a Manual J load calculation — actual sizing should be verified by an HVAC professional, especially for whole-house systems.
What this calculation does not cover
- This is a floor-area rule of thumb, not a load calculation. It reads only room length, width, a three-step ceiling category and a three-step sun category — insulation level, window area and glazing type, air leakage, wall and roof construction, and your local design temperatures are all outside it. It will not satisfy a permit, utility programme or contract that asks for a Manual J (or equivalent) load calculation.
- No internal heat gains are counted. Occupants, cooking, laundry, and electronics or server gear add load this model never sees, so a kitchen, a laundry room or a room that regularly holds several people needs more capacity than the figure shown.
- Ceiling height enters as a fixed multiplier on floor area, not as an actual volume. The real height of a vaulted ceiling, warm-air stratification, and an uninsulated roof or attic directly above the room make no difference to the result.
- The output is sensible cooling capacity only; it does not size for moisture removal. In a humid climate the latent load decides whether a nominally correct unit feels comfortable, and a unit chosen on capacity alone can short-cycle and leave the room cold and clammy.
- It sizes one enclosed room and stops there. Open-plan connections to the rest of the house, multi-room or whole-house distribution, duct and vent sizing, condensate drainage, the electrical supply for the unit, and the capacities actually sold are all outside the calculation.
Add the equipment this sizes
This result is a specification — 2,990 BTU/hr — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- Rule-of-thumb baseline: approximately 20 BTU per square foot for cooling, within a commonly cited 18-30 BTU/sq ft range depending on insulation, ceiling height, and climate
- A precise sizing should use a full Manual J load calculation performed by an HVAC professional — this tool gives a rough planning estimate only
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