How many BTU per square foot do I need?

The rule of thumb is 20 BTU per square foot of living space. A 300 sq ft room needs about 6,000 BTU before adjustments for ceiling height, climate, sun exposure, and occupants.

What size AC do I need for a 12x12 room?

A 12x12 room is 144 sq ft, which needs roughly 5,000 to 6,000 BTU after standard adjustments — a small window unit or a 0.5-ton mini-split.

Is it bad to oversize an air conditioner?

Yes. An oversized AC short-cycles — it cools fast but shuts off before removing humidity, leaving the room cold and clammy while wasting energy.

BTU Calculator — What Size AC Do I Need?

How big is the room?

Length × width of the space you want to cool.

Length (ft)

Width (ft)

Ceiling height (ft)

Standard is 8 ft. Taller ceilings need more cooling power.

What are the conditions?

Heat load depends on more than floor space.

Climate

HotDeep South, desert Southwest — long hot summers ModerateMidwest, Mid-Atlantic — warm but not brutal Cold / northernShort cooling season, mild summers

Sun exposure

SunnyLots of sun AverageSome sun ShadedTrees / north side

Is it a kitchen?

Yes No

Occupants

2

Your cooling size

You need

–

Room area: –
Base load: –
Adjustments: –
Shop for: –

💡 Pro field tips

🧰 Tools you'll need

Tap to check off as you load up.

Est. project cost (optional)

Unit price ($)

Install hours

Labor rate ($/hr)

Save to job log (optional)

File this estimate under a job name or PO to track what to order. Leave blank to file under "General".