How many BTU do I need per square foot?

The common sizing guideline is about 20 BTU per hour for each square foot of floor area. This calculator starts from that base and then applies the standard adjustments for sun, occupants and cooking heat.

Is a bigger air conditioner always better?

No. An oversized unit cools the air quickly but switches off before it removes enough humidity, leaving the room cold and clammy and wearing the compressor with frequent short cycles. Match the capacity to the room.

Is this a full HVAC load calculation?

No. This is a rule-of-thumb estimate for choosing a portable or window unit. For a fixed or ducted system, have an engineer carry out a proper room-by-room load calculation.

What is the Air Conditioner BTU Calculator?

Estimate the BTU cooling capacity a room air conditioner needs from the floor area, sun exposure, occupancy and whether it is a kitchen, using the standard sizing guideline. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Air Conditioner BTU Calculator

Name: Air Conditioner BTU Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Choosing a room air conditioner comes down to matching its cooling capacity, measured in BTU per hour, to the heat load of the space. This calculator starts from the widely used sizing guideline of about 20 BTU per square foot and applies the usual adjustments.

How it works

base   = floor area in sq ft × 20 BTU
sun    = +10% very sunny, −10% heavily shaded
people = +600 BTU for each occupant beyond two
kitchen= +4000 BTU for cooking heat

The result is rounded to a typical available unit size so you can shop against real model capacities.

Worked example

A 5 m × 4 m average-lit lounge for two people:

Area = 20 m² ≈ 215 sq ft
Base = 215 × 20 ≈ 4300 BTU
No sun, occupant or kitchen adjustment
Rounded ≈ 4500 BTU/hr

What to watch

Do not oversize. An air conditioner that is too powerful cools the air before it has run long enough to pull out humidity, so the room feels cold and damp and the compressor short-cycles.

This is a guideline, not a load calc. Ceiling height, insulation, glazing and climate all shift the real figure. For a permanent installation, get a professional load calculation rather than relying on a rule of thumb.