Measure the length and width of your room. Multiply its length and width together to get its square footage. For example, a room that has a length of 10 feet and a width of 10 feet has a square footage of 100 square feet.
Multiply the square footage by 25 to determine the recommended BTUs of your air conditioning system. For example: 25 x 100 = 2500 BTUs.
Increase the BTUs if your room is in a sunny location or has poor insulation. Add up to 50% to the total determined in step two:
2500 + .5 x 2500 = 3750 BTUs
Repeat steps 1-3 for any additional rooms. Add the totals calculated in step 3 together to get the total BTU rating for the ideal air conditioner size.
Things You Will Need
- Measuring tape
- Add more BTUs for rooms that have poorly insulated ceilings (+4000 BTUs), lots of windows that receive significant sunshine (+1500 BTUs per window) or rooms that commonly have two or more occupants (+400 BTUs per person).