Sizing calculator
What size air conditioner do you need?
Enter your room in square feet, tell us your climate and sun, and get a straight BTU and kW target, then the real, in-stock units that actually fit. No sign-up, nothing to install, no guesswork off a sticker.
Roughly 2.1 kW, or about 0.6 tons of cooling.
Sized for a 300 sq ft room (28 m²).
Units that fit your room
In-stock first
LG 11,000 BTU Portable Air ConditionerPortableFits your room11,000 BTU
Friedrich 7,200 BTU ZoneAire Select PTAC w/ Heat PumpWindowFits your room7,200 BTU$1,049Buy at Sylvane
Friedrich 7,000 BTU ZoneAire Select PTAC w/ Electric HeatWindowFits your room7,000 BTU$1,079Buy at Sylvane
Friedrich 7,000 BTU ZoneAire Premier PTAC w/ Electric Heat - 208-230VWindowFits your room7,000 BTU$1,089Buy at Sylvane
Ranked by how closely each unit’s rated coverage matches your sized room, in-stock first. Nobody pays for placement. Prices are live.
How we size it
The method behind the number
Most "BTU calculators" parrot a flat 20 BTU per square foot. That flat rate is not how ENERGY STAR's own chart actually works: the real ratio runs higher for a small room and lower for a large one, because heat gain scales with a room's exterior surface, not its floor area. We size against that official chart directly, then apply the ENERGY STAR room adjustments and a climate factor, because the same room in Phoenix and in Boston does not need the same air conditioner: the chart itself assumes a temperate summer, so hot and humid regions get real margin from the climate multiplier rather than a permanently inflated base number. It is the exact rule that drives every fit verdict, guide and recommendation on the rest of the site, so the number here never contradicts the unit pages it sends you to.
Room, honestly
Floor area is the biggest driver. A very sunny room adds roughly 10%, heavy shade subtracts 10%, a kitchen adds about 4,000 BTU, and every regular occupant beyond two adds about 600 BTU. High ceilings scale the load by volume, not floor area.
Climate, not guesswork
A hot, humid climate genuinely needs more cooling for the same room. We scale the target for hot regions (Florida, Texas, Arizona) and leave temperate regions alone rather than invent a number we cannot stand behind.
Matched to real stock
A target is useless without a unit that meets it. We rank the air conditioners whose rated coverage fits your room, in stock first, and show the live price. Nobody pays for placement.
Want the full reasoning? Read our guide to sizing an air conditioner or the .
Quick reference
Room size to BTU, at a glance
The cooling capacity ENERGY STAR recommends for a room, straight off its chart. Notice it is not a flat rate: the ratio falls from about 33 BTU per square foot in a small room to about 18 in a large one, because heat gets in through walls and windows, which grow slower than the floor. That is why a single "BTU per square foot" rule oversizes big rooms.
- Up to 150 sq ft5,000 BTU
- 150–250 sq ft6,000 BTU
- 250–300 sq ft7,000 BTU
- 300–350 sq ft8,000
Common questions
Air conditioner sizing, answered
What size air conditioner do I need for a 300 square foot room?
In a temperate climate a 300 sq ft room needs roughly 7,000 BTU (about 2.1 kW), the official ENERGY STAR chart's own recommendation. That rises with heat and humidity: the same room in a hot, humid climate like Florida needs closer to 9,000 BTU. A very sunny room, a kitchen, high ceilings or extra occupants push it up further. Enter your room above for the exact figure and the units that fit.
How many BTUs do I need per square foot?
The rule of thumb everyone quotes is a flat 20 BTU per square foot, but a flat rate is not how ENERGY STAR's own chart actually works: the real ratio runs higher for small rooms and lower for large ones, because heat gain scales with a room's exterior surface, not its floor area. We size against that official chart directly, then adjust for sun, ceiling height, kitchens, occupants and climate. As a quick guide (temperate climate): 150 sq ft is about 5,000 BTU, 300 sq ft about 7,000 BTU, 500 sq ft about 12,000 BTU, and 700 sq ft about 14,000 BTU.
Does my climate change what size air conditioner I need?
Yes, and it is the single biggest factor after room size. A hot, humid climate needs materially more cooling for the same room: we scale the target up by roughly 28% for Florida, 22% for Texas and 25% for Arizona, and leave temperate regions at the baseline. That is why a one-size-fits-all BTU chart under-sizes air conditioners across the Sun Belt. Set your region above and the number adjusts.