There are many factors that go into the formula to calculate the refrigeration of air conditioning that an AC unit must have to cool an environment. With this value we will be able to know which air conditioning to buy, remembering that the interior temperature sought is less than 25ºC.

Next, we will see what the factors are and how they influence the formula to calculate the fridges or watts of our air conditioning equipment. It is important to mention that the same formula applies to a split, mini-split, air conditioning, or portable equipment.

To make an approximate calculation of the power that an air conditioning unit needs to have to cool a room, it is necessary to take into account some factors. Below we explain what they are and how they intervene in the calculation.

Surface conductivity

Each material has a different conductivity of heat, depending on how much heat it passes through. Then, a different K constant is assigned depending on whether the walls are insulated or not and whether the windows have a single or double glass.

The value that the constant K will take is:

  • 0.692 (W / m2 / ºC), when the walls are insulated.
  • 1.09 (W / m2 / ºC), when the walls are not insulated.
  • 5.8 (W / m2 / ºC), when the windows have a simple glass.
  • 1.62 (W / m2 / ºC), when the windows have a double glass.

Surface to air conditioning

At this point we have to calculate the square meters of each wall, separating those that are isolated from those that are not. The surface of each window must also be calculated, differentiating those with double or single glass. Nor should we forget to add the surface of the ceiling and the floor. We will assign the letter S to the total surface to be air-conditioned.

Maximum outside temperature

Depending on the area where the house is located, it will have a maximum outdoor temperature in summer and winter. If we want to refrigerate, we are interested in knowing the thermal amplitude between the internal temperature that we want to obtain and the maximum external temperature in summer.

For example, if the desired interior temperature is 25ºC and the maximum in summer is 40ºC, the thermal amplitude, indicated as ΔT will be 15.

Air conditioning power calculation formula

When we have the calculation of the three previous factors, we can calculate without any problem the power that the refrigeration equipment would have to have to achieve a temperature below 25ºC.

The formula is as follows: P = K x S x (ΔT)

P indicates the power in kW, K is the material conductivity constant, S the surface, and ΔT the thermal amplitude.


Although this calculation is basic, it will give us an idea of ​​what air conditioning to buy for a certain room. But there are other factors that also intervene in the power calculation is the ventilation of the room.

Through this formula, heat loss due to air renewal is calculated.

PVentilation = (Specific weight of air x Specific heat of air) / 0.86 x V (number of vents) x ΔT between indoor and outdoor air.

The value obtained through this calculation is added to the power obtained.

Flashing coefficient

The letter C defines what is called the flashing coefficient and is intended to provide a little security to the power calculation. C varies from 1 to 2, depending on how much the home is used. The less you use the more the blinking coefficient will be.

So, if the house is used daily, C = 1.1, on the other hand, a weekend house will have a value of 1.4. This coefficient is multiplied by the total power of the calculated house.

If the air conditioner works perfectly, it is very likely that the cause is that it does not have enough power to remove heat from the environment.

In those cases, it is very useful to know how to calculate the refrigeration of an AC. In case the air conditioning has enough power, the problem can be found in poor maintenance.

Among the most common reasons for a lack of maintenance are the following: lack of cleaning in filters, lack of gas, among others.