Get an instant range from the conditions that change cooling load—then use it to challenge a quote based only on the old unit or square footage.
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Estimate a cooling-capacity range from conditioned floor area, climate, ceiling height, insulation, windows and internal heat—not square footage alone.
Instant result · no email requiredThis is a budgeting screen, not an ACCA Manual J calculation. Additions, duct losses, infiltration, construction assemblies and room-by-room airflow must be measured before equipment is ordered.
Moderate climate, average conditions. Hot-climate homes: step up one row. One ton = 12,000 BTU.
| Home size | Cooling needed | Typical system |
|---|---|---|
| 600–1,000 sq ft | 18,000–24,000 BTU | 1.5–2 tons |
| 1,000–1,500 sq ft | 24,000–30,000 BTU | 2–2.5 tons |
| 1,500–2,000 sq ft | 30,000–36,000 BTU | 2.5–3 tons |
| 2,000–2,500 sq ft | 36,000–42,000 BTU | 3–3.5 tons |
| 2,500–3,000 sq ft | 42,000–48,000 BTU | 3.5–4 tons |
| 3,000–3,500 sq ft | 48,000–60,000 BTU | 4–5 tons |
Intuition says bigger is safer. Air conditioning says otherwise: an oversized unit blasts the air cold and shuts off before pulling humidity out, so the house reads 72°F and feels like a locker room. The start-stop cycling also chews through compressor life and electricity. Right-sized systems run longer, gentler cycles — that's what comfort actually is.
Undersizing fails more visibly: the system runs all afternoon and never catches the setpoint. Either way you pay — which is why the answer worth trusting comes from a Manual J load calculation at your home, not a chart (including this one).
Sizing also drives price more than any other spec — a 2-ton and a 4-ton install are different quotes entirely. See what each size costs installed in our AC installation cost guide, or compare heat pump vs straight AC while you're choosing equipment.
As a rule of thumb, around 3 to 3.5 tons (36,000–42,000 BTU) in a moderate climate, rising toward 4 tons in hot-humid markets like Houston or Phoenix with poor shading. Ceiling height, insulation, window area and duct condition move the answer by half a ton either way — which is exactly what a Manual J load calculation pins down.
The common rule of thumb is 20–25 BTU per square foot: 20 in mild climates with good insulation, 25 or more in hot climates, sun-baked rooms or older leaky homes. Treat it as a starting estimate for budgeting, not a purchase spec.
It cools the air fast but shuts off before dehumidifying, leaving rooms cold and clammy, and the constant start-stop (short-cycling) wears the compressor and wastes power. Oversizing is the most common sizing mistake in the US housing stock — bigger is not safer.
It runs continuously on hot days without ever reaching the setpoint, driving up bills and shortening equipment life. If your current system runs nonstop every July and still loses ground by afternoon, undersizing (or duct leakage) is the usual culprit.
Manual J is the industry-standard room-by-room load calculation: it accounts for orientation, window specs, insulation levels, air leakage and local climate design temperatures. Any contractor quoting a replacement should perform one rather than matching the old unit's size — homes get re-insulated, windows get replaced, and the "same size as before" answer is wrong surprisingly often.
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