Tonnage Calculator — Air Conditioning Size Estimator
Estimate the right air-conditioning size for your space. Enter floor area, ceiling height, climate zone, sun exposure and insulation quality to get the recommended AC tonnage (tons of refrigeration), BTU/hr cooling load, and equivalent kilowatts.
Area unit
ft
Climate zone
Sun exposure
Insulation quality
people
Rounded up to the nearest half-ton for equipment sizing
- 1
Cooling load (BTU/hr)
1,200 × 25 × 1.125 × 1 × 1 × 1 + 2 × 400 = 34,550Area × 25 BTU/ft² × ceiling factor × climate × sun exposure × insulation quality. - 2
Exact tonnage
34,550 ÷ 12,000 = 2.879 - 3
Recommended AC size
⌈2.879 × 2⌉ ÷ 2 = 3Rounded up to the nearest half-ton to match standard equipment sizes.
How does this calculator work?
Estimate AC size with: BTU/hr = area (ft²) × 25 × ceiling/8 × climate × sun × insulation. Divide by 12,000 for tons (TR). A 1,500 sq ft, 9 ft ceiling, moderate climate, average conditions house needs roughly 1,500 × 25 × 1.125 × 1.0 × 1.0 × 1.0 ÷ 12,000 ≈ 3.5 TR, so a 3.5-ton unit. These are rule-of-thumb figures; a Manual J calculation gives precise sizing.
Formula
How this is calculated
Air-conditioning capacity is rated in tons of refrigeration (TR), where 1 TR = 12,000 BTU/hr of heat removal. The standard rule of thumb starts with a base load of 25 BTU/hr per square foot at 8 ft ceiling, moderate climate, average sun exposure and average insulation. This baseline is then scaled by four adjustment factors derived from common HVAC engineering practice.
The ceiling factor scales linearly: a 12 ft ceiling needs 50% more conditioning than an 8 ft ceiling (ratio = 12/8 = 1.5). Climate multipliers reflect typical outdoor design temperatures: very hot and humid climates (e.g. Gulf States, Southeast Asia) can require 40% more capacity than temperate zones. Sun exposure increases the solar heat gain through windows and roof; south-facing rooms with large windows can add 10%. Poor insulation allows more heat to conduct in from outside, adding up to 20%. Each occupant beyond two adds approximately 400 BTU/hr of sensible and latent heat.
The result is rounded up to the nearest half-ton because equipment comes in standard sizes (1, 1.5, 2, 2.5, 3 TR, etc.). These estimates are intended for preliminary planning. Proper sizing uses ACCA Manual J calculations that account for exact building geometry, window area and orientation, infiltration rates, duct losses, internal equipment loads, and local design-day conditions. Under-sizing causes the unit to run continuously and fail to maintain comfort; over-sizing causes short-cycling, poor dehumidification and higher energy bills.
Frequently asked questions
A common rule of thumb is 1 ton per 400–500 sq ft, so 1,000 sq ft typically needs 2–2.5 tons. However, this varies significantly with climate, insulation, ceiling height and sun exposure. In very hot climates or poorly insulated buildings, 1,000 sq ft might need 3 tons; in cool climates with good insulation, 1.5 tons may suffice.
One ton of refrigeration (1 TR) equals 12,000 BTU/hr of heat-removal capacity — the rate at which a one-short-ton (2,000 lb) block of ice melts in 24 hours. It is a unit of cooling power, not weight. 1 TR = 3.517 kW.
An oversized unit cools the air quickly but shuts off before removing enough humidity, leaving the space feeling clammy. It also cycles on and off frequently (short-cycling), which stresses the compressor and reduces its lifespan. The right-sized unit runs longer cycles, removes more moisture, and uses energy more efficiently.
Also known as
TG we-Calculate Editorial Team. (2026). Tonnage Calculator — Air Conditioning Size Estimator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/tonnage-calculator
TG we-Calculate Editorial Team. "Tonnage Calculator — Air Conditioning Size Estimator." TG we-Calculate. 2026. https://we-calculate.com/calculator/tonnage-calculator.
TG we-Calculate Editorial Team, "Tonnage Calculator — Air Conditioning Size Estimator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/tonnage-calculator
@misc{wecalculate_tonnage_calculator, title = {Tonnage Calculator — Air Conditioning Size Estimator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/tonnage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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