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AC Tonnage Calculator

Calculate the correct AC tonnage for your home based on square footage, climate zone, insulation quality, and other factors. 1 ton = 12,000 BTU/h.

How to Determine AC Tonnage

What Is AC Tonnage?

AC tonnage measures cooling capacity. 1 ton of cooling = 12,000 BTU/h — the amount of heat needed to melt one ton of ice in 24 hours. A 2-ton AC produces 24,000 BTU/h, a 3-ton produces 36,000 BTU/h, and so on. Residential central AC units range from 1.5 to 5 tons. Units above 5 tons are classified as commercial equipment.

Tonnage per Square Foot — Rules of Thumb

Tons = Total BTU / 12,000

Total BTU = Sq Ft × BTU/sq ft × Ceiling Factor × Insulation Factor × Sun Factor + Additions

Hot & Humid (South)→ 30 BTU/sq ft (~400 sq ft/ton)
Mixed Climate (Mid-Atlantic/Midwest)→ 25 BTU/sq ft (~480 sq ft/ton)
Cool Climate (Northeast)→ 20 BTU/sq ft (~600 sq ft/ton)

Standard residential AC sizes are: 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 5.0 tons. Always select the standard size that meets or slightly exceeds the calculated load.

Worked Example

Scenario: 2,000 sq ft home in mixed climate, good insulation, normal sun exposure, 8 ft ceilings, 4 occupants, 6 windows, includes kitchen.

  1. Base load = 2,000 × 25 × 1.0 × 1.0 × 1.0 = 50,000 BTU
  2. Occupant load = 4 × 400 = 1,600 BTU
  3. Window load = 6 × 1,000 = 6,000 BTU
  4. Kitchen addition = 4,000 BTU
  5. Total = 50,000 + 1,600 + 6,000 + 4,000 = 61,600 BTU
  6. Exact tonnage = 61,600 / 12,000 = 5.13 tons
  7. Since 5.13 > 5.0 (max residential), this home may need dual systems or a zoning solution.

Practical Tips

  • Never oversize your AC. An oversized unit short-cycles: it cools quickly but doesn't run long enough to remove humidity, leaving the air feeling clammy.
  • A properly sized AC should run 15–20 minutes per cycle during typical summer conditions.
  • For homes over 3,500 sq ft or with large second floors, consider zoned systems (two smaller units) instead of one oversized unit.
  • Upgrading insulation and sealing duct leaks can reduce the required tonnage by 1–2 tons, saving thousands on equipment costs.

Code References

ACCA Manual J, ASHRAE Fundamentals, DOE AC Sizing Guide

Related Calculators

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Frequently Asked Questions

How many square feet does a 1-ton AC cover?
A 1-ton AC (12,000 BTU/h) typically covers 400-600 square feet depending on climate, insulation, ceiling height, and sun exposure. In hot climates, expect closer to 400 sq ft per ton. In milder climates, up to 600 sq ft per ton. These are rough estimates — always verify with a proper Manual J calculation.
What are standard residential AC sizes?
Residential central AC units come in standard sizes: 1.5 tons (18,000 BTU), 2 tons (24,000 BTU), 2.5 tons (30,000 BTU), 3 tons (36,000 BTU), 3.5 tons (42,000 BTU), 4 tons (48,000 BTU), and 5 tons (60,000 BTU). For loads above 5 tons, most jurisdictions require commercial equipment.
Can I replace my AC with a larger size?
Not recommended. A larger AC will short-cycle, running for only a few minutes at a time. This causes: poor humidity control (the coil does not stay cold long enough to condense moisture), uneven temperatures, increased energy consumption (starting uses more power), and premature compressor failure. Always match the AC size to the actual load calculation.