One ton of air conditioning equals 12,000 BTU per hour, and most homes need 1 ton per 400–600 square feet — placing a typical 2,000 sq ft home in the 3–4 ton range. The exact tonnage depends on your climate zone, insulation quality, and building characteristics, which is why this guide provides detailed sizing charts rather than a single number.
Tonnage is the language contractors speak when quoting central AC systems. Understanding where your home falls on the tonnage chart saves you from the two most expensive sizing mistakes: buying too much capacity (wasting money and getting poor humidity control) or too little (running constantly without reaching setpoint).
AC Tonnage Chart by Square Footage
This is the most comprehensive tonnage chart available, covering all standard home sizes across five climate zones. Values assume average insulation and 8-foot ceilings.
| Home Size (sq ft) | Zone 2 (Hot) | Zone 3 (Warm) | Zone 4 (Mixed) | Zone 5 (Cool) | Zone 6 (Cold) |
|---|---|---|---|---|---|
| 500 | 1 ton | 1 ton | 1 ton | 1 ton | 1 ton |
| 750 | 1.5 ton | 1.5 ton | 1.5 ton | 1 ton | 1 ton |
| 1,000 | 2 ton | 1.5–2 ton | 1.5 ton | 1.5 ton | 1.5 ton |
| 1,200 | 2.5 ton | 2 ton | 2 ton | 1.5–2 ton | 1.5 ton |
| 1,500 | 3 ton | 2.5 ton | 2.5 ton | 2 ton | 2 ton |
| 1,800 | 3.5 ton | 3 ton | 2.5–3 ton | 2.5 ton | 2 ton |
| 2,000 | 3.5–4 ton | 3–3.5 ton | 3 ton | 2.5 ton | 2.5 ton |
| 2,200 | 4 ton | 3.5 ton | 3 ton | 3 ton | 2.5 ton |
| 2,500 | 4.5–5 ton | 4 ton | 3.5 ton | 3 ton | 3 ton |
| 2,800 | 5 ton | 4.5 ton | 4 ton | 3.5 ton | 3 ton |
| 3,000 | 5+ ton | 4.5–5 ton | 4 ton | 3.5 ton | 3–3.5 ton |
| 3,500 | 2-zone | 5 ton | 4.5–5 ton | 4 ton | 3.5 ton |
| 4,000 | 2-zone | 2-zone | 5 ton | 4.5 ton | 4 ton |
| 4,500 | 2-zone | 2-zone | 2-zone | 5 ton | 4.5 ton |
| 5,000 | 2-zone | 2-zone | 2-zone | 2-zone | 5 ton |
"2-zone" means you need two separate AC systems, typically one for each floor or wing. Residential AC units max out at 5 tons (60,000 BTU). Homes requiring more than 5 tons of cooling should be divided into zones with separate equipment, which also provides better comfort and redundancy.
Tonnage to BTU Conversion
| AC Tonnage | BTU/hr | Watts (approximate) | Amps at 240V |
|---|---|---|---|
| 1 ton | 12,000 | 880 | 3.7 |
| 1.5 ton | 18,000 | 1,320 | 5.5 |
| 2 ton | 24,000 | 1,760 | 7.3 |
| 2.5 ton | 30,000 | 2,200 | 9.2 |
| 3 ton | 36,000 | 2,640 | 11.0 |
| 3.5 ton | 42,000 | 3,080 | 12.8 |
| 4 ton | 48,000 | 3,520 | 14.7 |
| 5 ton | 60,000 | 4,400 | 18.3 |
Watts and amps are approximate for SEER2 16 equipment. Higher-efficiency units draw slightly less power per ton.
Square Feet Per Ton: The Quick Conversion
If you want to work backwards from tonnage to square footage, here's the rule of thumb by climate:
| Climate | Square Feet Per Ton |
|---|---|
| Hot-humid (Miami, Houston) | 350–450 sq ft per ton |
| Hot-dry (Phoenix, Las Vegas) | 400–500 sq ft per ton |
| Warm (Atlanta, Dallas) | 450–550 sq ft per ton |
| Mixed (Nashville, DC) | 500–600 sq ft per ton |
| Cool (Chicago, Boston) | 550–700 sq ft per ton |
| Cold (Minneapolis, Fargo) | 600–800 sq ft per ton |
These assume average insulation. Well-insulated homes push toward the higher end (more sq ft per ton = smaller system needed). Poorly insulated homes push toward the lower end.
Step-by-Step Tonnage Calculation
Method 1: Quick Estimate
Tonnage = Square footage ÷ Square feet per ton (from table above)
Example: 2,000 sq ft home in Dallas (warm climate, 500 sq ft per ton) Tonnage = 2,000 ÷ 500 = 4.0 tons
Method 2: BTU-Based Calculation
Tonnage = (Square footage × BTU per sq ft × Adjustment factors) ÷ 12,000
Example: 2,000 sq ft home in Dallas, average insulation, 9-ft ceilings BTU = 2,000 × 22 × 1.12 (ceilings) = 49,280 BTU Tonnage = 49,280 ÷ 12,000 = 4.1 tons → 4-ton system
Method 3: Full Load Calculation (Most Accurate)
Use our BTU calculator with all 12 adjustment factors, then divide by 12,000. This gets you within 5–10% of a professional Manual J.
Example 1: 1,800 sq ft two-story in Atlanta, GA (Zone 3)
- BTU calculation: 1,800 × 22 (Zone 3) = 39,600 base
- 9-ft ceilings: × 1.12 = 44,352
- Large windows, partial sun: +10% = 48,787
- Average insulation (2000 build): +0% = 48,787
- Open kitchen: +4,000 = 52,787
- Second floor rooms: included in sq ft
- Duct losses (attic): +15% = 60,705
Tonnage = 60,705 ÷ 12,000 = 5.06 tons → 5-ton system
Without the adjustment factors, the "quick estimate" would have given 3.5 tons (1,800 ÷ 500) — undersized by 30%.
Example 2: 1,200 sq ft new condo in Portland, OR (Zone 4)
- BTU calculation: 1,200 × 18 (Zone 4, low end for new build) = 21,600 base
- 8-ft ceilings: +0% = 21,600
- Small windows: −5% = 20,520
- Excellent insulation (2024 code): −15% = 17,442
- No kitchen adjustment (small galley): +2,000 = 19,442
- Ducts in conditioned space: −10% = 17,498
Tonnage = 17,498 ÷ 12,000 = 1.46 tons → 1.5-ton system
This new condo only needs 1.5 tons for 1,200 sq ft. Many contractors would reflexively quote 2.5 tons based on old rules of thumb — oversizing by 67%.
Example 3: 3,200 sq ft ranch in Phoenix, AZ (Zone 2)
- BTU calculation: 3,200 × 28 (Zone 2, high end) = 89,600 base
- 10-ft ceilings: × 1.25 = 112,000
- Massive west-facing windows: +25% = 140,000
- Below-average insulation (1988): +15% = 161,000
- Open kitchen: +4,000 = 165,000
- Slab on grade: +0% = 165,000
- Duct losses: +15% = 189,750
- Dry climate: −10% = 170,775
Tonnage = 170,775 ÷ 12,000 = 14.2 tons → Two-zone system (e.g., 5-ton + 5-ton, or 4-ton + 3.5-ton + supplemental)
This extreme example shows why Phoenix homes often need oversized or multi-zone systems. The west-facing windows and below-average insulation are the biggest drivers. Window tinting or exterior shading alone could reduce the load by 15–20%.
Available AC Tonnage Sizes and Models
Residential central air conditioners are manufactured in these standard sizes:
| Tonnage | BTU/hr | Typical Brands/Model Lines (2026) | Approx System Cost (installed) |
|---|---|---|---|
| 1.5 ton | 18,000 | Carrier 24ACC6, Trane XR13, Goodman GSXC7 | $3,000–$5,500 |
| 2 ton | 24,000 | Carrier 24ACC6, Lennox XC13, Rheem RA14 | $3,500–$6,000 |
| 2.5 ton | 30,000 | Carrier 24SPA6, Trane XR15, Goodman GSXC7 | $4,000–$7,000 |
| 3 ton | 36,000 | Carrier Infinity 24ANB6, Lennox XC21, Trane XV18 | $4,500–$8,000 |
| 3.5 ton | 42,000 | Carrier 24SPA6, Trane XR15, Rheem RA16 | $5,000–$9,000 |
| 4 ton | 48,000 | Carrier Infinity, Lennox SL28XCV, Trane XV20i | $5,500–$10,000 |
| 5 ton | 60,000 | Carrier Infinity, Lennox SL28XCV, Trane XV20i | $6,500–$12,000 |
Costs include outdoor condenser, indoor coil, refrigerant lines, labor, and permit. Excludes furnace/air handler replacement.
Tonnage and SEER2: How Efficiency Affects Your Decision
Higher-efficiency AC units cost more upfront but less to operate. Here's the annual operating cost comparison by tonnage and efficiency:
| Tonnage | SEER2 14 Annual Cost | SEER2 18 Annual Cost | SEER2 22 Annual Cost | SEER2 26 Annual Cost |
|---|---|---|---|---|
| 2 ton | $350 | $270 | $220 | $190 |
| 3 ton | $520 | $410 | $340 | $280 |
| 4 ton | $700 | $540 | $450 | $380 |
| 5 ton | $870 | $680 | $560 | $470 |
Based on 1,200 cooling hours/year at $0.15/kWh national average. Hot climates (2,000+ cooling hours) pay significantly more.
A 3-ton SEER2 22 system saves $180/year over SEER2 14. Over the system's 15–20 year lifespan, that's $2,700–$3,600 in savings — usually more than the efficiency upgrade cost.
When Your Home Needs Two Systems
Split systems become necessary when:
- Total load exceeds 5 tons (60,000 BTU) — the maximum for a single residential unit
- Two-story homes with poor duct access — separate systems per floor deliver much better comfort
- Long duct runs (over 50 feet) — efficiency drops significantly, making two shorter systems better
- Different occupancy patterns — if the upstairs bedrooms are empty during the day, a two-system approach lets you cool only what you use
When designing a two-system home, the typical split is:
| Floor | Tonnage Share | Why |
|---|---|---|
| First floor | 45–50% of total | Ground level, less roof exposure |
| Second floor | 50–55% of total | Heat rises, roof exposure, duct losses |
A 4,000 sq ft two-story home needing 7.5 total tons might use a 3.5-ton system for the first floor and a 4-ton system for the second floor.
Key Takeaways
- One ton = 12,000 BTU. Most homes need 1 ton per 400–600 sq ft depending on climate
- Standard residential AC sizes: 1.5 / 2 / 2.5 / 3 / 3.5 / 4 / 5 tons. Maximum single unit is 5 tons
- Climate zone is the biggest tonnage driver: a 2,000 sq ft home needs 2.5 tons in cool climates but 4 tons in hot climates
- Oversizing by one full ton (e.g., 4 ton where 3 ton is needed) wastes $100–$200/year in efficiency losses and creates humidity problems
- New homes (2020s code) need 20–40% less tonnage than older homes of the same square footage
- Homes over 3,000 sq ft in hot climates almost always need two systems
Frequently Asked Questions
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