Air Conditioner Size Calculator Formula
Understand the math behind the air conditioner size calculator. Each variable explained with a worked example.
Formulas Used
Recommended BTU
recommended_btu = (base_btu + occupant_adj) * sun_exposureIn Tons
recommended_tons = (base_btu + occupant_adj) * sun_exposure / 12000Variables
| Variable | Description | Default |
|---|---|---|
room_sqft | Room Area(sq ft) | 350 |
sun_exposure | Sun Exposure | 1 |
occupants | Usual Occupants | 2 |
base_btu | Derived value= room_sqft * 20 | calculated |
occupant_adj | Derived value= (occupants > 2) ? (occupants - 2) * 600 : 0 | calculated |
How It Works
How to Size an Air Conditioner
The general rule is 20 BTU per square foot. Adjust for sun exposure and occupancy.
Formula
Base BTU = Room Sq Ft x 20
Adjustments: +600 BTU per person over 2, +10% for sunny rooms, -10% for shaded.
1 ton = 12,000 BTU.
Worked Example
350 sq ft room, average sun, 2 occupants.
- 01Base BTU = 350 x 20 = 7,000
- 02Occupant adjustment = 0 (2 or fewer)
- 03Sun factor = 1.0 (average)
- 04Recommended BTU = 7,000 x 1.0 = 7,000 BTU
- 05In tons = 7,000 / 12,000 = 0.58 tons
Frequently Asked Questions
What happens if the AC is too small?
An undersized AC will run constantly, struggle to cool the room, waste energy, and may not reach the desired temperature on hot days.
What happens if the AC is too large?
An oversized AC will cool too quickly without removing humidity, causing a cold and clammy feel. It also cycles on/off frequently, reducing efficiency and lifespan.
Do I need to adjust for kitchen use?
Yes, if the AC cools a kitchen area, add 4,000 BTU to account for heat from cooking appliances.
Ready to run the numbers?
Open Air Conditioner Size Calculator