❄️ AC Tonnage Calculator
Size your air conditioner for home, office, or commercial space. Enter room dimensions, ceiling height, windows, doors, and sun exposure. Get recommended BTU and tons based on Manual J principles.
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Quick answer:
One ton of AC = 12,000 BTU/hr. A typical rule is 20–25 BTU per sq ft for base cooling, then add for ceiling height, people, windows, doors, and room type. A 200 sq ft bedroom with 8 ft ceilings and 2 windows often needs about 6,000–8,000 BTU (0.5–0.67 tons). Kitchen and sunny rooms need more.
AC Tonnage Calculator
How to calculate AC tonnage
- Measure your room’s floor area in square feet (length × width).
- Enter ceiling height. Standard is 8 ft; add about 1,000 BTU per extra foot.
- Choose room type. Kitchen adds ~4,000 BTU; basement/attic may need less or more depending on insulation.
- Set sunlight exposure. Sunny rooms need ~10% more; shaded rooms ~10% less.
- Add the number of windows (≈1,000 BTU each), exterior doors (≈1,000 BTU each), and occupants (≈600 BTU each).
- Click Calculate. The result shows BTU/hr and equivalent tons (BTU ÷ 12,000).
AC tonnage formula
Cooling load is estimated using Manual J-style factors:
- Base: Area (sq ft) × 25 BTU/sq ft × (ceiling height ÷ 8)
- + Occupants: 600 BTU per person
- + Windows: 1,000 BTU per window
- + Exterior doors: 1,000 BTU per door
- + Kitchen: 4,000 BTU when room type is Kitchen
- × Sun factor: 1.1 (sunny), 1.0 (normal), 0.9 (shaded)
Tons = BTU ÷ 12,000 (one ton of refrigeration = 12,000 BTU/hr)
Worked examples
- Example 1 (USA): 250 sq ft bedroom, 8 ft ceilings, 2 windows, 2 people, normal sun → ~7,000 BTU (0.58 tons). A 0.5–0.75 ton mini-split suits this room.
- Example 2 (UK): 400 sq ft living room, 9 ft ceilings, 4 windows, 1 door, 4 people, sunny → ~15,000 BTU (1.25 tons). A 1.5-ton unit provides headroom.
- Example 3: 150 sq ft kitchen, 8 ft ceilings, 2 windows, 2 people, sunny → ~10,000 BTU (0.83 tons). Kitchen heat adds significant load.
- Example 4: 1,200 sq ft open floor, 9 ft ceilings, 8 windows, 2 doors, 6 people, normal sun → ~45,000 BTU (3.75 tons). A 4-ton central AC or multiple zones would work.
How to interpret your results
| Tons | BTU/hr | Typical use |
|---|---|---|
| 0.5 | 6,000 | Small room (100–150 sq ft) |
| 1 | 12,000 | Single room (200–400 sq ft) |
| 1.5 | 18,000 | Large room or small apartment |
| 2 | 24,000 | 800–1,000 sq ft |
| 3 | 36,000 | 1,000–1,400 sq ft |
| 4 | 48,000 | 1,400–1,800 sq ft |
| 5 | 60,000 | 1,800–2,200 sq ft |
Frequently asked questions
One ton of refrigeration equals 12,000 BTU per hour. To convert tons to BTU, multiply by 12,000. For example, a 2-ton AC provides 24,000 BTU/hr cooling capacity.
Manual J is the ACCA (Air Conditioning Contractors of America) standard for sizing HVAC systems. It considers room area, ceiling height, windows, doors, occupants, and sun exposure to estimate cooling load in BTU.
Enter your room area in square feet, ceiling height, room type, number of windows and exterior doors, occupants, and sunlight exposure. The calculator applies Manual J principles to estimate BTU and converts to tons (BTU ÷ 12,000).
For 1,500 sq ft with 8 ft ceilings, typical cooling needs range from 22,500 to 37,500 BTU (about 2 to 3 tons), depending on ceiling height, windows, sun exposure, and occupants. Use the calculator with your specific inputs for a more accurate estimate.
36,000 BTU per hour equals 3 tons of refrigeration. Divide BTU by 12,000 to convert: 36,000 ÷ 12,000 = 3.
Yes. Kitchens typically add about 4,000 BTU to the cooling load due to heat from stoves, ovens, and appliances. The calculator applies this adjustment when Kitchen is selected as the room type.
Related calculators
Sources and notes
- ACCA Manual J — Residential load calculation standard (USA).
- ASHRAE Handbook — HVAC sizing principles and BTU factors.
This tool provides estimates only. For final sizing, consult a licensed HVAC professional. Last reviewed: March 2026