AC Tonnage vs Room Size:
The 2026 Square Foot Master Guide
The definitive room-to-tonnage reference for Indian homes. Accounts for top floors, sun-facing windows, high ceilings, and occupancy — not just square footage.
Quick-Match Room Grid
Hover over a room type to see tonnage details
Small Bedroom
80–120 sq ft
1.0T
Standard
Master Bedroom
150–180 sq ft
1.5T
Standard
Living Hall
220–280 sq ft
2.0T
Standard
Small Office
120–180 sq ft
1.5T
Standard
Master Reference Table
| Area (Sq. Ft) | Dimensions (ft) | Standard Tonnage | BTU/hr Range | Typical Rooms |
|---|---|---|---|---|
| 80–100 | 8×10 / 9×11 | 0.8T | 8,000–10,000 | Small bedroom, study |
| 100–120 | 10×10 / 10×12 | 1.0T | 10,000–12,000 | Bedroom, small office |
| 120–150 | 10×12 / 12×13 | 1.0T | 12,000–14,000 | Standard bedroom |
| 150–180 | 12×13 / 12×15 | 1.5T | 14,000–18,000 | Master bedroom, large bedroom |
| 180–220 | 13×15 / 15×15 | 1.5T | 18,000–22,000 | Large bedroom, small hall |
| 220–280 | 15×15 / 15×18 | 2.0T | 22,000–26,000 | Living room, drawing room |
| 280–350 | 15×20 / 18×20 | 2.0T | 26,000–32,000 | Large hall, open plan |
| 350–450 | 18×20 / 20×22 | 2.5T | 32,000–42,000 | Large hall, commercial space |
The "Rule of 10": How to Calculate Tonnage Manually
The formula every HVAC planner uses — simplified for Indian homes.
The Formula
Step 1: Area × 20 = Base BTU
e.g. 150 sq ft × 20 = 3,000... (simplified)
Step 2: BTU ÷ 12,000 = Tons
18,000 BTU ÷ 12,000 = 1.5 Ton
Top Floor: × 1.15
18,000 × 1.15 = 20,700 BTU → 2.0T
Why "Rule of 10"?
The simplified rule: 1 Ton per 100 sq ft (or 10×10 room). It's a rough guide — the actual formula accounts for ceiling height, occupancy, and solar gain. Use our calculator for precision.
Floor Height Factor
A 12-ft ceiling room needs ~15% more cooling capacity than the same sq ft with a 10-ft ceiling.
Why 1.5 Ton is the "Standard" for Indian Master Bedrooms
The data behind India's most popular AC size.
68%
of Indian master bedrooms are 140–180 sq ft
1.5T
covers 95% of master bedrooms in standard conditions
₹4,200
avg annual savings of 1.5T 5-star vs 3-star
The Indian master bedroom averages 150–170 sq ft — squarely in the 1.5T zone. This is why 1.5T accounts for over 55% of all AC sales in India. The 18,000 BTU output of a 1.5T unit is calibrated for this exact use case: 2 occupants, 10-ft ceiling, middle floor.
The only time you should deviate: top floor (go 2.0T), or a very small master bedroom under 130 sq ft (1.0T is sufficient and more efficient).
Factors that "Bump" Your Tonnage: Top Floors, Glass Windows, and Kitchens
These 6 conditions increase your room's heat load beyond the standard sq ft calculation.
Top Floor / Terrace
Roof absorbs solar radiation all day. Heat radiates down into the room even at night.
West-Facing Windows
Afternoon sun through west-facing glass adds 15–20% heat load. Use heavy curtains to mitigate.
Kitchen Adjacent
Cooking heat seeps through walls. Rooms next to kitchens run 3–5°C hotter.
High Ceiling (12+ ft)
Volume increases by 20% vs standard 10-ft ceiling. More air to cool = more tonnage needed.
4+ Occupants
Each person generates ~100W of body heat. 4 people = 400W extra load.
Large Glass Area (>30%)
Floor-to-ceiling glass or large bay windows dramatically increase solar gain.
Multiple Factors? Add them up.
Top floor (+0.5T) + west-facing windows (+0.25T) + 4 occupants (+0.25T) = +1.0T total. A room that would normally need 1.5T now needs 2.5T. Use our Precision Tonnage Calculator to account for all factors simultaneously.
What Happens if You Buy the Wrong Size?
Short-cycling vs. under-cooling — both destroy efficiency and lifespan.
Undersized AC
- Runs continuously at 100% — never reaches set temperature
- Compressor overheats and fails prematurely (3–5 years vs 10+)
- Electricity bill 30–40% higher than a correctly sized unit
- Humidity not removed — room feels sticky even when 'cool'
Oversized AC
- Short-cycling: cools too fast, shuts off, restarts repeatedly
- Humidity not removed — short cycles don't run long enough to dehumidify
- Higher upfront cost with no efficiency benefit
- Compressor wear from frequent start-stop cycles
The Golden Rule
When in doubt between two sizes, choose the larger one — but only if it's an inverter AC. An inverter compressor can throttle down to 30–40% capacity, making slight oversizing harmless. A fixed-speed AC cannot — oversizing a fixed-speed unit causes short-cycling.
BTU to Ton Converter & Reference
Reading a product label? Convert BTU to tonnage instantly.
BTU → Ton Quick Converter
Enter BTU from a product label to find the tonnage
| BTU/hr | Tonnage | kW | Room Size |
|---|---|---|---|
| 8,000 | 0.8T | 2.3 kW | Small bedroom (80–100 sq ft) |
| 10,000 | 1.0T | 2.9 kW | Bedroom (100–120 sq ft) |
| 12,000 | 1.0T | 3.5 kW | Standard bedroom (120–150 sq ft) |
| 18,000 | 1.5T | 5.3 kW | Master bedroom (150–180 sq ft) |
| 24,000 | 2.0T | 7.0 kW | Living room (220–280 sq ft) |
| 30,000 | 2.5T | 8.8 kW | Large hall (280–350 sq ft) |
| 36,000 | 3.0T | 10.5 kW | Commercial space (350–450 sq ft) |
Frequently Asked Questions
A 1.5 Ton 5-star inverter AC is ideal for a 150 sq ft room. If it's on the top floor or has large west-facing windows, still go with 1.5T but choose a model with a high ISEER (5.0+) to handle the extra load efficiently.
Still Not Sure? Use the Precision Calculator
Enter your exact dimensions, floor, windows, and occupancy for a 100% accurate recommendation.