Air Conditioner Sizes
Cooling capacity in BTU and cabinet dimensions for window, portable, mini-split, and central air-conditioning systems.
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Last reviewed on 2026-05-02.
Proper AC sizing ensures efficient cooling and energy savings. This guide covers BTU requirements by room size, window AC dimensions, portable units, mini-splits, and central air system sizing.
AC Size by Room Square Footage
| Room Size | Recommended BTU | Tonnage | AC Type |
|---|---|---|---|
| 100-150 sq ft | 5,000 BTU | 0.4 ton | Small window AC |
| 150-250 sq ft | 6,000 BTU | 0.5 ton | Window AC |
| 250-300 sq ft | 7,000 BTU | 0.6 ton | Window AC |
| 300-350 sq ft | 8,000 BTU | 0.7 ton | Window/Portable AC |
| 350-400 sq ft | 9,000 BTU | 0.75 ton | Large window AC |
| 400-450 sq ft | 10,000 BTU | 0.8 ton | Portable/Mini-split |
| 450-550 sq ft | 12,000 BTU | 1 ton | Mini-split |
| 550-700 sq ft | 14,000 BTU | 1.2 ton | Mini-split |
| 700-1,000 sq ft | 18,000 BTU | 1.5 ton | Mini-split/Central AC |
| 1,000-1,200 sq ft | 21,000 BTU | 1.75 ton | Central AC |
| 1,200-1,400 sq ft | 23,000 BTU | 2 ton | Central AC |
| 1,400-1,600 sq ft | 28,000 BTU | 2.5 ton | Central AC |
| 1,600-1,900 sq ft | 34,000 BTU | 3 ton | Central AC |
| 1,900-2,200 sq ft | 42,000 BTU | 3.5 ton | Central AC |
| 2,200-2,600 sq ft | 47,000 BTU | 4 ton | Central AC |
| 2,600-3,000 sq ft | 60,000 BTU | 5 ton | Central AC |
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Window AC Unit Dimensions
| BTU Rating | Width | Height | Depth | Weight |
|---|---|---|---|---|
| 5,000 BTU | 16-18" | 12-13" | 12-15" | 40-50 lbs |
| 8,000 BTU | 19-21" | 13-15" | 14-18" | 55-70 lbs |
| 10,000 BTU | 20-24" | 14-16" | 16-20" | 65-80 lbs |
| 12,000 BTU | 22-25" | 15-17" | 18-22" | 75-95 lbs |
How to Calculate AC Size
Basic Formula
Square footage × 20 BTU = Required cooling capacity. Example: 300 sq ft × 20 = 6,000 BTU minimum.
Adjust +10% for sunny rooms, +4,000 BTU for kitchens, +600 BTU per person over 2
Factors Affecting AC Size
Ceiling Height: Standard 8 ft ceilings. Add 10% for 10 ft ceilings. Sun Exposure: Add 10% for south-facing rooms. Reduce 10% for heavily shaded rooms. Insulation: Well-insulated homes need less capacity. Climate: Hot, humid climates need 20-30% more capacity. Kitchen: Add 4,000 BTU. Occupants: Add 600 BTU per person beyond first two people.
Window AC vs Central Air
Window AC: 5,000-12,000 BTU, cools single room, $150-500, easy DIY install. Portable AC: 8,000-14,000 BTU, mobile, dual-hose more efficient, $250-700. Mini-Split: 9,000-36,000 BTU per zone, quiet, energy efficient, $1,500-4,000 installed. Central AC: 1.5-5 tons (18,000-60,000 BTU), whole-house cooling, $3,000-8,000 installed.
AC Sizing Mistakes
Oversized AC: Cycles on/off frequently, doesn't dehumidify properly, wastes energy. Undersized AC: Runs constantly, can't cool room, higher electric bills. Ignoring Ceiling Height: 10-12 ft ceilings need 20-30% more capacity than standard 8 ft.
Energy Efficiency
EER (Energy Efficiency Ratio): BTU ÷ watts. Higher is better. Min 10 EER for window units. SEER (Seasonal Energy Efficiency Ratio): For central AC. Minimum 14 SEER (2023+ US standard). 16+ SEER recommended for efficiency. Inverter Technology: Variable-speed compressors save 30-50% energy vs. single-speed.