CADR is the number that decides whether an air purifier will actually work in your room, yet many listings bury it under a big coverage claim. This guide explains what it means and shows the sums for typical Singapore rooms.
You can also use the calculator on our home page. Type in your room and it highlights the listings that state a big enough number.
What CADR means
CADR is clean air delivery rate, the volume of purified air a unit delivers each hour. It is usually quoted in m³/h, or sometimes in CFM. To convert CFM to m³/h, multiply by about 1.7.
A higher CADR means the unit cleans the room faster. It is measured by standard test methods, but a seller's figure on a cheap listing is not always independently verified.
The sizing formula
Room volume = length × width × ceiling height. Required CADR = room volume × air changes per hour. For everyday dust and odours, four air changes an hour is a good target. For allergies, pets and haze, aim for five or six.
The formula assumes a closed room. Open doors and big gaps make the sums optimistic.
Worked examples for Singapore rooms
A 12 m² HDB bedroom with a 2.6 m ceiling is about 31 m³. At five air changes an hour, you need about 155 m³/h.
A 16 m² master bedroom is about 42 m³, so around 210 m³/h. A 20 m² living room is about 52 m³, so around 260 m³/h. A 30 m² open-plan living and dining area is about 78 m³, so around 390 m³/h.
Round up to the next size available. A unit with spare capacity can run on a quieter speed.
Why coverage claims in m² can mislead
Coverage figures are often calculated at a low number of air changes an hour, or at the maximum fan speed. A listing that says 'covers 60 m²' may be rated for a lot less in practice.
If a listing only gives m², choose one that is rated for noticeably more than your room, and treat the claim as the seller's, not as a measurement.
Noise and CADR go together
A purifier with a high CADR can reach your target on a low speed. That is why buying one size up is common. A small unit at maximum speed can hit the number but will be loud.
Check the noise level at the speed that gives the CADR, not just at the lowest setting.
Frequently asked questions
What CADR do I need for a 12 m² bedroom?
About 155 m³/h at five air changes an hour, assuming a 2.6 m ceiling. Choose a unit with a bit more if you want to run it quietly.
How do I convert CFM to m³/h?
Multiply CFM by about 1.7. A purifier rated at 100 CFM delivers roughly 170 m³/h.
Does a higher CADR use more electricity?
It usually uses more power at maximum speed, but a high-CADR unit on a low speed can use less than a small unit running flat out.
