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BTU / AC Size Calculator

A BTU calculator sizes a room air conditioner so it actually cools the space without short-cycling. Enter the room area, how much sun it gets, how many people use it and whether it is a kitchen, and it returns a cooling load and rounds it up to the nearest standard unit size.

Your measurements

Result

Because the result is a specific unit size, the shopping list shows window and portable ACs at that size — and HVAC installers for anyone who would rather have it fitted. That dual intent is why this page carries both product and lead CTAs.

How it is calculated

We start at roughly 20 BTU per square foot, then adjust: +10% for very sunny rooms, −10% for shaded ones, +600 BTU per person beyond two, and +4,000 BTU for kitchens. The result is rounded up to the nearest standard size so you never undersize.

Steps

Enter the room area in square feet.
Pick the sun exposure — a very sunny room needs more cooling.
Enter how many people are usually in the room.
Say whether it is a kitchen (cooking adds heat).
Read the recommended BTU and shop units at that size, or get an installer.

Worked example

A 300 sq ft average room used by two people works out to about 6,000 BTU, which rounds to a 6,000 BTU unit.

Common questions

What size air conditioner do I need?

About 20 BTU per square foot as a base, adjusted for sun, people and kitchens. The calculator turns that into a standard unit size.

Why round up to the next size?

An undersized unit runs constantly and never quite cools the room. A slightly oversized window or portable unit is fine.

Does ceiling height matter?

Yes — the 20 BTU rule assumes 8 ft ceilings. For taller rooms, step up one size.

Window, portable or mini-split?

Window units are cheapest and most efficient; portables are easiest to install; mini-splits are quietest and best for permanent cooling.