US: 3.5 ton (42,000 BTU/hr) covers roughly 2,250 sq ft of whole-home area in a moderate climate — 1,700 sq ft in a hot climate, 2,850 sq ft in a cool one. That works out to about 18.7 BTU per sq ft. Note that the rate is lower than for a small room: envelope area grows more slowly than floor area, so larger homes need fewer BTU per square foot.
India: a 3.5 ton split serves about 420 sq ft of a single room, at the hot-climate room rate of roughly 100 BTU per sq ft. Top floor under an RCC roof, or a large west-facing window, and you should treat that as the upper limit rather than the target.
| US climate zone | Area covered | Effective rate |
|---|---|---|
| Zone 1 — Hot (FL, S.TX, AZ desert) | 1,700 sq ft | 24.7 BTU/sq ft |
| Zone 2 — Warm (Deep South, TX) | 1,950 sq ft | 21.5 BTU/sq ft |
| Zone 3 — Moderate (TN, NC, MO) | 2,250 sq ft | 18.7 BTU/sq ft |
| Zone 4 — Mild (Mid-Atlantic, PNW) | 2,500 sq ft | 16.8 BTU/sq ft |
| Zone 5 — Cool (Upper Midwest, New England) | 2,850 sq ft | 14.7 BTU/sq ft |
Working the other way? The AC size chart by area starts from square footage instead.
| US climate zone (whole home) | Coverage |
|---|---|
| Zone 1 — Hot (FL, S.TX, AZ desert) | ~428 sq ft |
| Zone 2 — Warm (Deep South, TX) | ~480 sq ft |
| Zone 3 — Moderate (TN, NC, MO) | ~545 sq ft |
| Zone 4 — Mild (Mid-Atlantic, PNW) | ~600 sq ft |
| Zone 5 — Cool (Upper Midwest, NE) | ~666 sq ft |
| India climate (single room) | Coverage |
|---|---|
| Hot & Dry (Delhi, Jaipur, Nagpur) | ~130 sq ft |
| Hot & Humid (Mumbai, Chennai, Kolkata) | ~133 sq ft |
| Composite (Lucknow, Hyderabad) | ~144 sq ft |
| Temperate (Bengaluru, Pune) | ~179 sq ft |
India figures are per room at typical 9.5 ft ceilings; subtract ~10% for top-floor rooms under an RCC roof, since the roof factor consumes part of the capacity.
| AC size | BTU/hr | US coverage | India (per room) |
|---|---|---|---|
| 0.75 ton | 9,000 | 360–500 sq ft | 75–100 sq ft |
| 1 ton | 12,000 | 480–666 sq ft | 100–133 sq ft |
| 1.5 ton | 18,000 | 720–1,000 sq ft | 150–200 sq ft |
| 2 ton | 24,000 | 960–1,333 sq ft | 200–266 sq ft |
| 2.5 ton | 30,000 | 1,200–1,666 sq ft | 250–333 sq ft |
| 3 ton | 36,000 | 1,440–2,000 sq ft | 300–400 sq ft |
| 3.5 ton | 42,000 | 1,680–2,333 sq ft | 350–466 sq ft |
| 4 ton | 48,000 | 1,920–2,666 sq ft | 400–533 sq ft |
| 5 ton | 60,000 | 2,400–3,333 sq ft | 500–666 sq ft |
About 2,250 sq ft in a moderate US climate, ranging from 1,700 sq ft in a hot climate to 2,850 sq ft in a cool one. In hot Indian conditions a 3.5 ton split serves about 420 sq ft of a single room.
42,000 BTU per hour, since one ton equals 12,000 BTU/hr.
US figures are whole-home loads for an insulated envelope at moderate outdoor temperatures. Indian figures are single-room loads in hot conditions with higher ceilings and stronger solar gain, which runs near 100 BTU per sq ft instead of about 22.