1 ton vs 1.5 ton AC: which size to buy?
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Quick answer
Brands in India commonly recommend a 1 ton AC for rooms up to about 120 sq ft and a 1.5 ton AC for roughly 150 to 220 sq ft. Go one size up if the room is on the top floor, gets strong afternoon sun or has many people in it. Oversizing is not free: a bigger AC draws more power. Measure the room first, then use the calculator below.
Who this is for
Anyone buying an AC for a bedroom, study or living room who is unsure whether 1 ton or 1.5 ton is enough.
What “ton” means
AC tonnage is cooling capacity, not weight. One ton is 12,000 BTU an hour, which is about 3.517 kW of heat removed. A 1.5 ton AC is rated for 18,000 BTU an hour.
A larger tonnage can remove more heat, but it also draws more electricity at full load. The BEE star rating and ISEER on the label tell you how efficiently a given model does it.
Room size rule of thumb
Multiply length by breadth in feet to get the area. A 10 x 12 ft bedroom is 120 sq ft; a 14 x 15 ft room is 210 sq ft. The gap between 120 and 150 sq ft is a judgement call, which is where the adjustments below matter.
| Room area | Suggested capacity |
|---|---|
| Up to about 120 sq ft | 1 ton |
| About 150 to 220 sq ft | 1.5 ton |
| Above 220 sq ft | Check a 2 ton model, or ask the brand to size it for the room |
When to go one size up
The reverse also holds. A shaded room on a middle floor with one occupant can be comfortable with the smaller size, and an oversized unit in a small room cycles on and off more than it needs to.
- Top floor or a roof above the room: the ceiling gets hot, so the room gains more heat.
- West or south-facing windows with direct afternoon sun: more heat enters through the glass.
- More than two people, or a kitchen opening into the room: people and appliances add heat.
- A very large window area: glass lets in more heat than a wall.
Running cost: a worked example
Our calculator uses this formula: units per hour = tonnage x 3.517 / ISEER, at full rated capacity. Actual running load is lower once the room has cooled. With an ISEER of 4.5, a 1 ton AC works out to about 0.78 units an hour and a 1.5 ton AC to about 1.17 units an hour.
Over 8 hours that is roughly 6.2 units against 9.4 units a day. Multiply by your own tariff per unit to see the difference. The 1.5 ton unit uses about half as much again, so choosing it for a room that a 1 ton AC would cool is money wasted every month.
Things people forget
- The star rating and ISEER matter as much as the tonnage. Compare ISEER numbers on the BEE label of the exact models.
- Inverter ACs vary compressor speed, which helps when a unit is slightly larger than the room needs. See our inverter vs non-inverter explainer.
- Check the pipe length and installation charges, which are extra for both sizes.
- If you are in between sizes, ask the brand or an installer to size it for your room, orientation and floor.
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Frequently asked questions
Is a 1.5 ton AC too big for a bedroom?
For a bedroom of about 120 sq ft or less, a 1 ton AC is the usual recommendation. A 1.5 ton AC suits a larger bedroom, or a smaller one with strong sun, a top-floor ceiling or several occupants.
Does a 1.5 ton AC use more electricity than a 1 ton AC?
At the same ISEER, yes: by the formula, 1.5 ton draws 1.5 times the power at full load. A more efficient 1.5 ton model can still cost less to run than a poor 1 ton one, so compare ISEER.
How many square feet does a 1.5 ton AC cool?
Makers such as Onida suggest about 150 to 220 sq ft as a rule of thumb. Sun, floor and occupants move that range.
Is 1.5 ton enough for 250 sq ft?
It is borderline. Onida calls it marginal and suggests a larger unit unless the room is well shaded. Ask the brand to size a bigger model for you.
How do I measure my room?
Multiply length by breadth in feet. Our tonnage helper in the calculator also accepts square metres.
Sources
Checked on . Rules can change, so confirm with the official page before you travel or buy.