ilovecalculator.my
☰

Air Purifier Clean-Up Time Calculator

Enter your room size, the purifier's CADR and the PM2.5 levels to estimate how long it takes to clean the room's air. This is an idealised estimate for a closed room.

m²

Length × width of the room. Keep the door and windows closed.

m

A typical room is about 2.4–3 m.

m³/h

The smoke or PM2.5 CADR on the purifier's box or specs, in m³/h. Multiply CFM by 1.7 to get m³/h.

µg/m³

The PM2.5 level in the room now.

µg/m³

The level you want, for example 15 µg/m³ or lower.

Source: AHAM Verifide – Air filtration standards (CADR) ↗

This result is an estimate only. Check with your bank or the relevant authority before making decisions.

How it is calculated

  • Room volume = floor area × ceiling height
  • Air changes per hour = CADR ÷ room volume
  • Time (hours) = ln(starting PM2.5 ÷ target PM2.5) ÷ air changes per hour
  • Time (minutes) = hours × 60

This assumes a sealed room with well-mixed air and no new pollution. To find the CADR you need for a room, use the air purifier size calculator. To see how bad the air is, use the PM2.5 to US AQI calculator.

Worked example

A 20 m² room with a 2.7 m ceiling is 54 m³. A purifier with a CADR of 270 m³/h gives 270 ÷ 54 = 5 air changes an hour. Going from 150 to 15 µg/m³:

  • ln(150 ÷ 15) = ln(10) = 2.303
  • Time = 2.303 ÷ 5 = 0.46 hours, about 28 minutes

Why your number may differ

Treat this as a best case. Doors, gaps and people coming and going let polluted air in. Purifier performance drops as filters clog and at lower fan speeds. PM2.5 sensors vary by a few µg/m³. Indoor sources such as cooking and candles add particles. This is general information, not medical advice.

Frequently asked questions

How is the time worked out?

A purifier removes a fixed share of the room's particles each hour, equal to its CADR divided by the room volume. PM2.5 therefore falls exponentially, and the time is ln(start ÷ target) ÷ air changes per hour.

Why does it take longer in real life?

Real rooms leak, new particles come in from outside, and a purifier's CADR is measured in a test chamber. Open doors and windows make the estimate far too low.

Is a bigger CADR always better?

A higher CADR cuts the time proportionally, but it can be louder and cost more. Match the CADR to the room size first. The air purifier size calculator shows what to aim for.

Related calculators