Room Air Conditioner Size Chart: BTU by Room Size 2026

The chart gives the base size — then the room adjusts it

An air conditioner that is too small runs all day and never cools the room; one that is too big cools fast, shuts off, and never dries the air — so the room feels clammy. The right size starts with the room area: the standard chart (ENERGY STAR / manufacturer guidance) lists the base BTU for each room size, from 5,000 BTU for up to 150 sq ft to 34,000 BTU for up to 2,500 sq ft. Then the room adjusts it: sunny rooms need 10% more, shaded rooms 10% less, kitchens add 4,000 BTU, each person past the first two adds 600 BTU, and taller ceilings scale the size by height divided by 8. Needed BTU = base × sun factor + 4,000 if kitchen + 600 × people over 2, then × height / 8, rounded to the nearest BTU. Buy-this-size = the smallest standard size at or above the needed BTU. On the defaults — 300 sq ft, 8 ft ceilings, average sun, no kitchen, 2 people — the base BTU is 7,000, the needed BTU is 7,000, and you buy a 7,000 BTU unit.

At the defaults — room area 300 sq ft, ceiling height 8 ft, sun exposure average, kitchen no, people 2 — the base BTU is 7,000, the needed BTU is 7,000, and the buy-this-size is 7,000 BTU. Check the identities: base = the table row for the area; needed = round(base × sun + kitchen + 600 × max(0, N − 2)) × H / 8; buy = the smallest standard size at or above the needed BTU. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

The worked example, line by line

Setup: room area 300 sq ft, ceiling height 8 ft, sun exposure average, kitchen no, people 2.

Line 1 — the base BTU. 300 sq ft falls in the up-to-300 row: 7,000 BTU.

Line 2 — the sun adjustment. Average sun, so the factor is 1.00: 7,000 × 1.00 = 7,000 BTU.

Line 3 — the kitchen adjustment. No kitchen, so add nothing: still 7,000 BTU.

Line 4 — the people adjustment. 2 people, so nobody past the first two: add nothing, still 7,000 BTU.

Line 5 — the ceiling adjustment. 8 ft ceilings, so × 8 / 8 = 1.00: 7,000 BTU.

Line 6 — the buy-this-size. The smallest standard size at or above 7,000 BTU is 7,000 BTU.

Now the same room as a sunny kitchen with 4 people and 10-foot ceilings: base 7,000 × 1.10 = 7,700; + 4,000 for the kitchen = 11,700; + 600 × 2 for the extra people = 12,900; × 10 / 8 = 16,125 BTU; the smallest standard size at or above that is 18,000 BTU. The base chart says 7,000 BTU; the adjustments more than double it.

Reverse: the BTU for 500 sq ft is 12,000 (the 450–550 row); at 500 sq ft the base is 12,000, at 450 sq ft it is 10,000. The largest room for a 9,000 BTU unit is 400 sq ft (the 350–400 row); 401 sq ft needs 10,000 BTU. Sunny vs shaded at 300 sq ft: sunny needs 7,700, so buy 8,000 BTU; shaded needs 6,300, so buy 7,000 BTU. A kitchen at 300 sq ft needs 11,000, so buy 12,000 BTU. The occupants that push 300 sq ft up a size: 2 people buy 7,000 BTU, 3 people need 7,600, so buy 8,000 BTU. The ceiling height that pushes 300 sq ft up a size: 8 ft buys 7,000 BTU, 9 ft needs 7,875, so buy 8,000 BTU.

Every branch, checked

Room 150 sq ft: base 5,000 BTU, needed 5,000 BTU — Base 5,000 BTU, needed 5,000 BTU — buy a 5,000 BTU unit. The smallest row: up to 150 sq ft needs 5,000 BTU, and 5,000 BTU is the smallest standard size — buy a 5,000 BTU unit.

Room 200 sq ft: base 6,000 BTU, needed 6,000 BTU — Base 6,000 BTU, needed 6,000 BTU — buy a 6,000 BTU unit. Up to 250 sq ft needs 6,000 BTU — buy a 6,000 BTU unit.

Room 400 sq ft: base 9,000 BTU, needed 9,000 BTU — Base 9,000 BTU, needed 9,000 BTU — buy a 9,000 BTU unit. Up to 400 sq ft needs 9,000 BTU — buy a 9,000 BTU unit.

Room 600 sq ft: base 14,000 BTU, needed 14,000 BTU — Base 14,000 BTU, needed 14,000 BTU — buy a 14,000 BTU unit. Up to 700 sq ft needs 14,000 BTU — buy a 14,000 BTU unit.

Room 1,000 sq ft: base 18,000 BTU, needed 18,000 BTU — Base 18,000 BTU, needed 18,000 BTU — buy a 18,000 BTU unit. Up to 1,000 sq ft needs 18,000 BTU — buy an 18,000 BTU unit.

Room 2,500 sq ft: base 34,000 BTU, needed 34,000 BTU — Base 34,000 BTU, needed 34,000 BTU — buy a 34,000 BTU unit. The largest row: up to 2,500 sq ft needs 34,000 BTU — buy a 34,000 BTU unit. Anything bigger is above the table.

Sunny, 300 sq ft: base 7,000 BTU, needed 7,700 BTU — Base 7,000 BTU, needed 7,700 BTU — buy a 8,000 BTU unit. A sunny 300 sq ft room needs 7,700 BTU — 7,000 × 1.10 — and the smallest standard size at or above that is 8,000 BTU, so buy an 8,000 BTU unit. The sun alone pushes the room up a size.

Shaded, 300 sq ft: base 7,000 BTU, needed 6,300 BTU — Base 7,000 BTU, needed 6,300 BTU — buy a 7,000 BTU unit. A shaded 300 sq ft room needs 6,300 BTU — 7,000 × 0.90 — and the smallest standard size at or above that is 7,000 BTU, so buy a 7,000 BTU unit. Shade does not drop the size here, because 6,300 is above the 6,000 BTU unit.

Kitchen, 300 sq ft: base 7,000 BTU, needed 11,000 BTU — Base 7,000 BTU, needed 11,000 BTU — buy a 12,000 BTU unit. A 300 sq ft kitchen needs 11,000 BTU — 7,000 + 4,000 for the cooking heat — and the smallest standard size at or above that is 12,000 BTU, so buy a 12,000 BTU unit. The kitchen alone pushes the room up two sizes.

4 people, 300 sq ft: base 7,000 BTU, needed 8,200 BTU — Base 7,000 BTU, needed 8,200 BTU — buy a 9,000 BTU unit. Four people in a 300 sq ft room need 8,200 BTU — 7,000 + 600 × 2 — and the smallest standard size at or above that is 9,000 BTU, so buy a 9,000 BTU unit.

3 people, 300 sq ft: base 7,000 BTU, needed 7,600 BTU — Base 7,000 BTU, needed 7,600 BTU — buy a 8,000 BTU unit. Three people in a 300 sq ft room need 7,600 BTU — 7,000 + 600 — and the smallest standard size at or above that is 8,000 BTU, so buy an 8,000 BTU unit. One extra person is enough to push the room up a size.

10 ft ceilings, 300 sq ft: base 7,000 BTU, needed 8,750 BTU — Base 7,000 BTU, needed 8,750 BTU — buy a 9,000 BTU unit. Ten-foot ceilings in a 300 sq ft room need 8,750 BTU — 7,000 × 10 ÷ 8 — and the smallest standard size at or above that is 9,000 BTU, so buy a 9,000 BTU unit.

9 ft ceilings, 300 sq ft: base 7,000 BTU, needed 7,875 BTU — Base 7,000 BTU, needed 7,875 BTU — buy a 8,000 BTU unit. Nine-foot ceilings in a 300 sq ft room need 7,875 BTU — 7,000 × 9 ÷ 8 — and the smallest standard size at or above that is 8,000 BTU, so buy an 8,000 BTU unit. One extra foot of ceiling is enough to push the room up a size.

12 ft ceilings, 300 sq ft: base 7,000 BTU, needed 10,500 BTU — Base 7,000 BTU, needed 10,500 BTU — buy a 12,000 BTU unit. Twelve-foot ceilings in a 300 sq ft room need 10,500 BTU — 7,000 × 12 ÷ 8 — and the smallest standard size at or above that is 12,000 BTU, so buy a 12,000 BTU unit.

Combo: sunny + kitchen + 4 people + 10 ft, 300 sq ft: base 7,000 BTU, needed 16,125 BTU — Base 7,000 BTU, needed 16,125 BTU — buy a 18,000 BTU unit. Everything at once: a sunny 300 sq ft kitchen with 4 people and 10-foot ceilings needs 16,125 BTU — (7,000 × 1.10 + 4,000 + 1,200) × 10 ÷ 8 — and the smallest standard size at or above that is 18,000 BTU, so buy an 18,000 BTU unit. The base chart says 7,000 BTU; the adjustments more than double it.

What the defaults assume

The model assumes the standard room-size BTU table (ENERGY STAR / manufacturer guidance): up to 150 sq ft → 5,000 BTU; up to 250 → 6,000; up to 300 → 7,000; up to 350 → 8,000; up to 400 → 9,000; up to 450 → 10,000; up to 550 → 12,000; up to 700 → 14,000; up to 1,000 → 18,000; up to 1,200 → 21,000; up to 1,400 → 23,000; up to 1,500 → 24,000; up to 2,000 → 30,000; up to 2,500 → 34,000. It assumes 8-foot ceilings as the baseline, an average-insulated room, and that the room is a normal living space — a sunroom, a server room, or a room with a dozen people needs a proper load calculation. Rooms over 2,500 sq ft are above the table: the calculator reports above the table — use multiple units (a model-level edge, not a validation error — room areas up to 5,000 sq ft are accepted). With a 100 sq ft room the answer is 5,000 BTU (the smallest unit); with a 50 sq ft room it is also 5,000 BTU (below the table — the smallest unit still applies). Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The renter cooling a 300 sq ft bedroom: they learn a 7,000 BTU unit is right — and they check the sunny branch (8,000 BTU) before buying, because the bedroom faces west.
• The homeowner cooling a 300 sq ft kitchen: they learn the kitchen needs 11,000 BTU, so they buy a 12,000 BTU unit — the base chart's 7,000 BTU would have left the kitchen warm every evening.
• The family of four in a 300 sq ft living room: they learn four people need 8,200 BTU, so they buy a 9,000 BTU unit — and they check the 3-person branch (8,000 BTU) to see how much one extra person matters.
• The owner of a loft with 12-foot ceilings: they learn 12-foot ceilings need 10,500 BTU in a 300 sq ft room, so they buy a 12,000 BTU unit — and they check the combo branch (18,000 BTU) when the loft is also a sunny kitchen.

Accuracy & limitations

The chart is the standard room-size BTU table used by ENERGY STAR and the manufacturers: 5,000 BTU up to 150 sq ft, 6,000 up to 250, 7,000 up to 300, 8,000 up to 350, 9,000 up to 400, 10,000 up to 450, 12,000 up to 550, 14,000 up to 700, 18,000 up to 1,000, 21,000 up to 1,200, 23,000 up to 1,400, 24,000 up to 1,500, 30,000 up to 2,000, and 34,000 up to 2,500. The adjustments are the standard rules of thumb: sunny +10%, shaded −10%, kitchen +4,000 BTU, +600 BTU per person over two, and × height / 8 for ceilings. What the model cannot do is a proper Manual J load calculation — insulation, window size and direction, climate zone, and heat from appliances all move the real answer, and a room over 2,500 sq ft needs more than one unit. For the ceiling fan to go with it, see the ceiling fan size chart; for the filter size, see the air filter size chart; for backup power for the unit, see the generator size chart. This is a calculator, not an HVAC design.