What Size Central AC Do I Need?
Enter your home's square footage and climate zone to find the right air conditioner tonnage. Covers 1-ton through 5-ton central AC systems with SEER guidance.
Updated for 2026 SEER2 standards and current federal tax credit eligibility.
On this page: Calculator · Tonnage chart · SEER guide · When to replace · Alternatives · FAQ
Cooling a single room? Use the window AC, portable AC, or mini split calculator instead. For a detailed room-by-room BTU breakdown, use the advanced BTU calculator.
Quick answer
1 ton of AC per 400–600 sq ft, depending on climate. A 1,500 sq ft home typically needs a 2.5–3 ton system. A 2,500 sq ft home needs 3.5–5 tons. One ton of cooling = 12,000 BTUs per hour.
This calculator estimates whole-home central AC tonnage. For room-by-room calculations, use the advanced BTU calculator. For a code-compliant load calculation, get an HVAC quote that includes a Manual J.
AC tonnage chart by home size
This table shows typical central AC tonnage for average insulation in a mixed climate (Zone 4). Adjust up one size for hot climates (zones 1–2) or poor insulation. Adjust down for cool climates (zones 5–6) or excellent insulation.
| Home size (sq ft) | Tonnage | BTUs | Common system |
|---|---|---|---|
| 600–1,000 | 1.5 ton | 18,000 | Small home, condo, apartment |
| 1,000–1,300 | 2 ton | 24,000 | Small ranch, townhouse |
| 1,300–1,600 | 2.5 ton | 30,000 | Average 3-bedroom home |
| 1,600–2,000 | 3 ton | 36,000 | Typical 3–4 bedroom home |
| 2,000–2,400 | 3.5 ton | 42,000 | Larger 4-bedroom home |
| 2,400–3,000 | 4 ton | 48,000 | Large home, 2-story 4–5 bedroom |
| 3,000–3,600 | 5 ton | 60,000 | Large 2-story or hot climate |
| 3,600+ | 5+ ton or dual system | 60,000+ | Very large home — get HVAC quotes |
Central AC systems come in half-ton increments (1.5, 2, 2.5, 3, 3.5, 4, 5 tons). If your calculation falls between sizes, match the nearest — don't automatically round up. See “what happens if my AC is too big” below.
SEER ratings explained
SEER (Seasonal Energy Efficiency Ratio) measures how efficiently an AC converts electricity into cooling. Higher SEER = lower electricity bills. The US switched from SEER to SEER2 in 2023, but the concept is the same.
| SEER2 rating | Efficiency level | Best for | Approx. cost premium |
|---|---|---|---|
| 14.3–15 | Minimum (baseline) | Cool climates, low usage | Baseline |
| 16–17 | Good | Mixed climates, moderate usage | +10–20% |
| 18–20 | High efficiency | Hot climates, heavy usage | +20–40% |
| 21+ | Ultra-high / variable speed | Hot climates, max savings, premium comfort | +40–60% |
The payback period depends on your climate and electricity rate. In Phoenix (Zone 2, $0.12/kWh), upgrading from 15 to 20 SEER saves roughly $200–350 per year and pays back in 5–8 years. In Seattle (Zone 4), savings are smaller because the AC runs fewer hours. The energy cost calculator shows your specific numbers. Use the SEER savings calculator to compare specific ratings with your electricity rate.
Check for federal tax credits on high-efficiency systems. Energy Star certified units (typically 16+ SEER2) may qualify for credits of $300–$2,000 depending on system type and efficiency level.
When to replace your central AC
Central AC systems last 15–20 years on average. Here's how to decide between repairing and replacing:
| Factor | Repair | Replace |
|---|---|---|
| Age | Under 10 years | Over 15 years |
| Repair cost | Under 50% of new system | Over 50% of new system |
| Refrigerant | R-410A (current) | R-22 (phased out, expensive) |
| SEER rating | 13+ SEER | Under 10 SEER (pre-2006) |
| Repair frequency | First major repair | 2+ major repairs in 3 years |
If replacing, this is the time to get the size right. Many homes have oversized AC systems because the original installer used a rule of thumb instead of a load calculation. Use the calculator above to verify your current system is the right size before buying the same tonnage again.
A smart thermostat can extend the life of both old and new systems by reducing unnecessary runtime. It also provides diagnostic data that helps catch problems before they become expensive repairs.
Supplementing an aging system? A space heater for shoulder-season heating and a ceiling fan for perceived cooling can extend the life of your current AC while you plan a replacement.
Alternatives to central AC
Central AC isn't always the best or most cost-effective option. Here's when other cooling systems may be a better fit:
| Alternative | Best for | Sizing tool |
|---|---|---|
| Ductless mini split | No ductwork, additions, single zones, year-round heating+cooling | Mini split calculator |
| Window AC | Single rooms, renters, supplemental cooling, low budget | Window AC calculator |
| Portable AC | Rooms where windows won't support a unit, garages, temporary cooling | Portable AC calculator |
| Heat pump | Year-round heating and cooling in one system, zones 1–5 | Heat pump calculator |
| Ceiling fan | Supplemental comfort, extends AC effectiveness by 3–4°F | Ceiling fan calculator |
A mini split is often the best value when installing from scratch (no existing ductwork), because you avoid the $3,000–$7,000 cost of new duct installation — plus mini splits have zero duct loss, making them inherently more efficient.
Reduce cooling load before buying
Before sizing up your AC, consider improvements that reduce the load itself. These can sometimes let you drop down a half-ton, saving $500–$1,500 on equipment:
Weatherstripping ($5–15) — seal air leaks that let hot air in. Window film / insulation ($10–30) — reduce solar heat gain through windows. Clean HVAC air filters ($15–30) — dirty filters reduce airflow and efficiency by 5–15%. Find your exact size with the air filter calculator.
A thermal leak detector ($25–40) shows exactly where your home is gaining heat. Focus improvements there first. Also check your air filter size — the wrong size filter is as bad as no filter.
Frequently asked questions
What size central AC do I need for a 2,000 square foot house?
A 2,000 sq ft home typically needs a 3-ton (36,000 BTU) to 4-ton (48,000 BTU) central AC. In hot climates like Phoenix or Houston (zones 1–2), lean toward 3.5–4 tons. In mild climates like Seattle or the Pacific Northwest (zone 4), 3 tons is usually sufficient. The calculator above accounts for your specific climate, insulation, and home characteristics.
How many tons of AC do I need per square foot?
The rough rule is 1 ton per 400–600 sq ft: 1 ton per 400 sq ft in hot climates (zones 1–2), 1 ton per 500 sq ft in mixed climates (zone 4), and 1 ton per 600 sq ft in cool climates (zones 5–6). This is a starting point — insulation, ductwork, sun exposure, and ceiling height all shift the number. For room-specific calculations, use the advanced BTU calculator.
What SEER rating should I look for?
The 2023 federal minimum is 14.3 SEER2 in the North and 15 SEER2 in the South. For good efficiency, aim for 16–17 SEER2 in mixed climates and 18+ SEER2 in hot climates where the AC runs 1,500+ hours per year. Use the SEER savings calculator to compare the annual cost difference between ratings at your electricity price.
What happens if my AC is too big for my house?
An oversized AC short-cycles: it drops the temperature quickly, then shuts off before removing enough humidity. This causes clammy, uncomfortable air despite a correct thermostat reading. Short-cycling also wastes energy (startup is the least efficient phase) and stresses the compressor. A right-sized system that runs longer cycles provides better comfort, lower humidity, and lower energy bills. This is why the tonnage chart says to match the nearest size rather than automatically round up.
Is this calculator for central AC only?
Yes. This calculator sizes whole-home central AC systems (split systems with an outdoor condenser and indoor air handler connected by ductwork). For single-room cooling, use the window AC calculator or portable AC calculator. For ductless whole-home cooling, the mini split calculator sizes multi-zone systems. For a ducted heat pump (heating + cooling in one), use the heat pump calculator. For a room-by-room breakdown with 12 variables, use the advanced BTU calculator.
How much does a new central AC system cost?
Installed cost for a new central AC ranges from roughly $3,500 for a 2-ton baseline system to $8,000–$12,000 for a 4–5 ton high-efficiency system, depending on your area and contractor. Ductwork modifications can add $1,000–$5,000. Get multiple HVAC quotes and verify each includes a load calculation — not just matching the old system's tonnage. Federal tax credits may offset 30% of the cost for qualifying high-efficiency systems.
Maximize your new AC's efficiency
A smart thermostat can cut cooling costs 10–15% by adjusting when you're away or asleep. Top picks for central AC: ecobee (best room sensors), Google Nest (best learning), Honeywell Home (best compatibility). The energy cost calculator can estimate your annual savings.