Buying an air purifier without knowing if it is large enough for your room is a waste of money. A device that is too small for the space must run continuously at its highest setting to be effective, which causes both noise pollution and extra wear and tear. Below, we explain step by step how to calculate the correct CADR for your room.
Step 1: determine the volume of your room
CADR is expressed in cubic meters of air per hour (m3/h), so you need the volume of your space, not just the floor area. Calculate this using:
Volume (m3) = length (m) x width (m) x ceiling height (m)
A living room of 5 x 4 meters with a standard ceiling height of 2.5 meters therefore has a volume of 5 x 4 x 2.5 = 50 m3.
Step 2: choose the desired number of air changes per hour
How many times per hour you want to refresh the air (the so-called ACH, air changes per hour) depends on your situation:
- 2x per hour: basic level, suitable for general use without specific concerns
- 4x per hour: recommended level for most households, including those with mild allergies
- 5 to 6x per hour: for people with asthma, severe allergies, pets, or if someone in the house smokes
You can read more about this topic in our article on how often an air purifier should refresh the air per hour.
Step 3: calculate the required CADR
The formula is simple:
Required CADR (m3/h) = volume of the room (m3) x desired number of air changes per hour
For our example room of 50 m3, with a desired level of 4 air changes per hour, you arrive at 50 x 4 = 200 m3/h of required CADR.
Calculation example for a larger space
Suppose you have a living room of 55 m2 with a ceiling height of 2.5 meters; the volume is 55 x 2.5 = 137.5 m3. At 2 air changes per hour, you arrive at approximately 275 m3/h; at 4 air changes, this increases to 550 m3/h. For such a space, a standard device is often insufficient, and it is better to opt for a device with a higher CADR or to combine multiple air purifiers.
Rule of thumb as a quick check
Don't feel like calculating? A simple rule of thumb (based on the AHAM guideline) is that the CADR should be at least two-thirds of your floor area in square meters. For a room of 30 m2, this means a CADR of at least approximately 200 m3/h, assuming you have an average ceiling height and want a moderate number of air changes.
Take the "suitable up to" rating into account
Manufacturers often state a maximum room size, for example "suitable up to 55 m2." This value is usually based on a limited number of air changes per hour (often 2x). If you want a higher level of air purification, such as for allergies, it is better to calculate with a smaller maximum room size than what is on the packaging, or choose a device with some extra capacity.
Example: the AirPure Plus PA244
The Dynter AirPure Plus PA244 has a CADR of 260 m3/h and is suitable for up to 55 m2. For an average living room or bedroom of 20 to 40 m2, this means the device can run on a lower, quieter setting while still achieving a good number of air changes per hour, with a noise level between 28 and 60 dB, depending on the chosen setting.
Our advice
Always calculate using the volume of your room, not just the floor area, and prefer a model with slightly more CADR than the absolute minimum. This way, the device does not have to run continuously at the highest, loudest setting to remain effective.