Window AC
5,000–24,000 BTU
Sits in a double-hung window and cools one room. The cheapest way to add cooling.
- Installed cost
- $300–$1,100
- Install
- DIY, about 30 minutes
- Efficiency
- Good
- Noise indoors
- Moderate
Best for: Single rooms and rentals
AC size chart: BTU and tons by square feet
Type your square footage and the chart marks your row, so it works as a quick AC tonnage calculator. Room sizes follow the ENERGY STAR chart; whole-house sizes follow typical central AC tonnage.
Short answer
Rooms: about 20 BTU per sq ft (a 12×15 bedroom ≈ 6,000 BTU). Whole homes: about 1 ton per 500–600 sq ft, so a 2,000 sq ft house usually needs 3.5–4.5 tons.
LOOKUP
Single rooms (ENERGY STAR)
| Room area | Metric | BTU/h | Tons | Best fit |
|---|---|---|---|---|
| 100–150 ft² | 9–14 m² | 5,000 | 0.42 | Window / portable |
| 150–250 ft² | 14–23 m² | 6,000 | 0.50 | Window / portable |
| 250–300 ft² | 23–28 m² | 7,000 | 0.58 | Window / portable |
| 300–350 ft² | 28–33 m² | 8,000 | 0.67 | Window / portable |
| 350–400 ft² | 33–37 m² | 9,000 | 0.75 | Window or mini-split |
| 400–450 ft² | 37–42 m² | 10,000 | 0.83 | Window or mini-split |
| 450–550 ft² | 42–51 m² | 12,000 | 1.00 | Window or mini-split |
| 550–700 ft² | 51–65 m² | 14,000 | 1.17 | Window or mini-split |
| 700–1,000 ft² | 65–93 m² | 18,000 | 1.50 | Mini-split or small central |
| 1,000–1,200 ft² | 93–111 m² | 21,000 | 1.75 | Mini-split or small central |
| 1,200–1,400 ft² | 111–130 m² | 23,000 | 1.92 | Mini-split or small central |
| 1,400–1,500 ft² | 130–139 m² | 24,000 | 2.00 | Mini-split or small central |
| 1,500–2,000 ft² | 139–186 m² | 30,000 | 2.50 | Central AC or multi-zone |
| 2,000–2,500 ft² | 186–232 m² | 34,000 | 2.83 | Central AC or multi-zone |
Whole house (central AC)
| Home size | Metric | AC tons |
|---|---|---|
| 1,000 ft² | 93 m² | 1.5 – 2 |
| 1,200 ft² | 111 m² | 2 – 2.5 |
| 1,500 ft² | 139 m² | 2.5 – 3 |
| 1,600 ft² | 149 m² | 3 – 3.5 |
| 1,800 ft² | 167 m² | 3 – 4 |
| 2,000 ft² | 186 m² | 3.5 – 4.5 |
| 2,200 ft² | 204 m² | 4 – 5 |
| 2,500 ft² | 232 m² | 4.5 – 5 |
| 3,000 ft² | 279 m² | 5+ |
HVAC sizing terms, defined
- BTU (British Thermal Unit)
- The heat needed to raise one pound of water by 1°F. AC capacity is rated in BTU per hour: how much heat the unit removes from a room each hour.
- Ton (of cooling)
- 12,000 BTU per hour. A 3-ton central AC removes 36,000 BTU per hour.
- SEER2
- Seasonal Energy Efficiency Ratio 2, the DOE efficiency rating for central AC and heat pumps since 2023. A higher number means less electricity for the same cooling.
- EER / CEER
- Efficiency at a single operating point, used for window and portable units. Watts drawn = BTU ÷ EER.
- Manual J
- The ACCA load calculation contractors use to size a whole-house system from insulation, windows, orientation and climate.
- Short cycling
- An oversized unit turning on and off too often. It wears parts faster and removes less humidity.
Adjust for ceiling height
The charts assume 8 ft ceilings. For higher ceilings multiply the BTU by your height ÷ 8: a 10 ft ceiling needs about 25% more.
| Ceiling | Multiply BTU by |
|---|---|
| 8 ft | × 1.00 |
| 9 ft | × 1.13 |
| 10 ft | × 1.25 |
| 12 ft | × 1.50 |
Common rooms, sized
- Bedroom 10×12 ft (120 ft²): 5,000 BTU.
- Primary bedroom 14×16 ft (224 ft²): 6,000 BTU, or about 7,000 if it gets strong afternoon sun.
- Living room 16×22 ft (352 ft²): 9,000 BTU.
- Open kitchen + living 20×25 ft (500 ft²): 12,000 + 4,000 for the kitchen = 16,000 BTU.
- Studio apartment 600 ft² with its kitchen: 14,000 + 4,000 for the kitchen = 18,000 BTU.
BTU CONVERTER
1 ton = 12,000 BTU/h = 3.517 kW · 1 kW = 3,412 BTU/h
Which type of air conditioner fits your room?
Once you know the BTU, the type decides the cost: a window unit for one room is a few hundred dollars, a ductless mini-split a few thousand, and central air for the whole house five figures.
Portable AC
5,000–14,000 BTU
Rolls on the floor and vents hot air through a hose to a window. Easy to move, but the least efficient type.
- Installed cost
- $250–$950
- Install
- No tools, about 10 minutes
- Efficiency
- Lowest
- Noise indoors
- Loudest
Best for: Windows that do not fit a window unit, HOA rules
Ductless mini-split
6,000–36,000 BTU
A quiet wall unit connected to an outdoor inverter compressor. Cools and heats, room by room.
- Installed cost
- $2,500–$6,000
- Install
- Licensed installer
- Efficiency
- Highest
- Noise indoors
- Quietest
Best for: Additions, garages, homes without ducts
Central AC
18,000–60,000 BTU
An outdoor unit and indoor coil that cool the whole house through ductwork, controlled by one thermostat.
- Installed cost
- $5,300–$10,500
- Install
- Licensed installer
- Efficiency
- High (SEER2-rated)
- Noise indoors
- Quiet
Best for: Whole homes that already have ducts
Installed cost: HomeGuide 2026 (mini-split shown as a single-zone system). Efficiency and noise are relative comparisons between types.
Frequently asked questions
What size AC do I need for a 1,500 sq ft house?
Usually 2.5–3 tons (30,000–36,000 BTU) for a central AC, depending on climate and insulation.
What size AC do I need for a 2,000 sq ft house?
Typically 3.5–4.5 tons. Hot climates and poorly insulated homes sit at the top; mild climates at the bottom.
How many square feet does a 3-ton AC unit cover?
A 3-ton (36,000 BTU) central AC usually serves about 1,500–1,800 sq ft. In a hot climate or a poorly insulated house, the same home may need 3.5 tons or more.
What are the standard AC sizes?
Central air conditioners come in half-ton steps from 1.5 to 5 tons (18,000–60,000 BTU). Mini-split indoor heads run from 6,000 to 36,000 BTU, and window and portable units mostly from 5,000 to 24,000 BTU.
Is it bad to oversize an air conditioner?
Yes. It short-cycles, removes less humidity, wears out faster and costs more up front. Match the chart, then adjust for sun and occupancy.
Best HVAC Repair GuideAC size chart: BTU and tons by square feet
Updated
ScaleNot to scale — national price ranges
Sources
Estimates for planning only. Prices vary by region, home, and contractor. Gas, refrigerant, and high-voltage work must be done by a licensed technician.