How many BTUs do I need per square foot?

The ENERGY STAR chart works out near 20 to 25 BTU per sq ft for small rooms and less for larger ones. Use the chart, not a flat rate.

Does ceiling height change the BTUs?

The chart assumes 8 feet. Higher ceilings hold more air; this tool scales by height.

Can I use this for a whole house?

No. Use it for one room. A whole house needs a Manual J.

Does a kitchen need more BTUs?

Yes. ENERGY STAR adds 4,000 BTU for a kitchen.

HyreHVAC tools

BTU calculator: how many BTUs does a room need?

A room cooling estimate from ENERGY STAR’s published chart and adjustments. For a whole house, use a Manual J.

7,000 BTU/hr a 250 to 300 sq ft room, 8 ft ceiling ENERGY STAR room air conditioner sizing chart. Adjust for sun, people, kitchen and ceiling height.

The short answer

This BTU calculator estimates the cooling a single room needs, in BTU per hour.

It uses the ENERGY STAR room sizing chart, which assumes an 8-foot ceiling, then applies ENERGY STAR’s own adjustments: 10% less for a heavily shaded room, 10% more for a very sunny one, 600 BTU per person beyond two, and 4,000 BTU for a kitchen.

A 300 sq ft room starts at 7,000 BTU per hour.

Work out the BTUs

One room. Nothing is emailed.

— Cooling needed

— In tons

— In kW

— Chart starting point

What this assumed

—

A room estimate from ENERGY STAR’s chart. Not a Manual J. HyreHVAC does not size or install equipment.

What does the ENERGY STAR chart say?

Room area (sq ft)	Capacity (BTU per hour)
100 to 150	5,000
150 to 250	6,000
250 to 300	7,000
300 to 350	8,000
350 to 400	9,000
400 to 450	10,000
450 to 550	12,000
550 to 700	14,000
700 to 1,000	18,000
1,000 to 1,200	21,000
1,200 to 1,400	23,000
1,400 to 1,500	24,000
1,500 to 2,000	30,000
2,000 to 2,500	34,000

ENERGY STAR sizing chart for room air conditioners, calculated for an 8-foot ceiling.

How does the calculator adjust the chart?

Ceiling height: the chart assumes 8 feet, so we scale by your height divided by 8. That is our assumption, based on air volume, not an ENERGY STAR rule.

Sun: ENERGY STAR says to cut capacity 10% for a heavily shaded room and add 10% for a very sunny one. People: add 600 BTU for each regular occupant beyond two. Kitchen: add 4,000 BTU.

The result also shows tons (12,000 BTU per hour each) and kilowatts (3,412 BTU per hour each).

What this BTU number is for

Choosing a window, portable or mini-split head for one room
The chart was built for that.
Checking a quote for a single zone
If a quote is far off, ask why.
Not for sizing a whole-house system
A central system needs an ACCA Manual J load calculation.
Not for heating
Heating loads depend on your winter design temperature and insulation. See the furnace sizing calculator.

Why not just buy bigger?

An oversized unit cools the air fast and shuts off before it removes much moisture, so the room feels cold and clammy. It also starts and stops more often. Slightly undersized is usually the smaller mistake for cooling.

Questions this calculator answers

How many BTUs do I need per square foot?: The ENERGY STAR chart works out near 20 to 25 BTU per sq ft for small rooms and less for larger ones. Use the chart, not a flat rate.
How many BTUs is a ton?: 12,000 BTU per hour.
Does ceiling height change the BTUs?: The chart assumes 8 feet. Higher ceilings hold more air; this tool scales by height.
Can I use this for a whole house?: No. Use it for one room. A whole house needs a Manual J.
Does a kitchen need more BTUs?: Yes. ENERGY STAR adds 4,000 BTU for a kitchen.

Sources and methodology

Figures dated October 26, 2026. Last reviewed September 18, 2026.

ENERGY STAR: Certified Room Air Conditioners, sizing guidance (ENERGY STAR, retrieved 2026-10-26. Room area to capacity chart for an 8-foot ceiling, with shade, sun, occupant and kitchen adjustments.)
ACCA: Manual J, Residential Load Calculation (ACCA, retrieved 2026-10-26. The ANSI-recognised method for sizing heating and cooling equipment to a house.)

Mini split sizing calculator Several rooms, head by head
AC sizing calculator Whole-house tonnage screen
BTU The unit explained
HVAC tonnage Tons and BTUs

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