How is the BTU figure calculated?

It starts from about 20 BTU per square foot of floor area, then adjusts ±10% for sun exposure (×1.1 sunny, ×0.9 shaded) and adds roughly 600 BTU for each occupant beyond two. The total is rounded up to the nearest 100.

What size air conditioner do I need for my room?

As a rule of thumb, multiply the floor area in square feet by 20. A 12 m² (about 129 sq ft) room needs roughly 2600 BTU/hr before adjustments — enter your room to get a tailored figure.

How do I adjust for a sunny or shaded room?

A sunny, south-facing room gains more heat, so the tool raises the estimate by 10%. A heavily shaded room lowers it by 10%. Pick the option that matches your room.

Why add BTU for extra people?

Each person gives off body heat, so the calculator adds about 600 BTU for every occupant above the baseline of two, which adds to the cooling load.

Does it account for metres as well as feet?

Yes. Enter dimensions in metres and the tool converts to feet (÷ 0.3048) before applying the 20 BTU per square foot rule.

Is this a substitute for a professional load calculation?

No. It is a quick sizing guide for a single room. Ceiling height, insulation, climate and appliances all affect real cooling load, so confirm with an installer for a permanent system.

Is anything uploaded?

No — every calculation happens in your browser and nothing is sent to a server.

BTU Air Conditioner Calculator

BTU air conditioner calculator — size your unit

A BTU calculator estimates the cooling capacity an air conditioner needs for a room. Enter the room size, pick the sun exposure, and set how many occupants the room usually has. The tool returns a recommended capacity in BTU per hour — a practical starting point for choosing a unit.

How it works

The base figure uses the common rule of 20 BTU per square foot:

BTU = floor area (sq ft) × 20

It then applies a sun factor (×1.1 for sunny, ×0.9 for shaded, ×1.0 normal) and adds 600 BTU per occupant above two. The result is rounded up to the nearest 100.

Example

A 4 m × 3 m room (12 m² ≈ 129 sq ft), normal sun, 2 people:

Base = 129 × 20 ≈ 2583 BTU
Sun factor (normal) = ×1.0 → 2583
Occupants = 2, no addition
Rounded up → ≈ 2600 BTU/hr

Room	Sun	People	Recommended
12 m²	Normal	2	≈ 2600 BTU/hr
12 m²	Sunny	4	≈ 4100 BTU/hr

This is a quick single-room guide, not a professional load calculation. Everything runs in your browser with nothing uploaded.