The short answer
Under about 30 dB on low is whisper-quiet for a bedroom; 40 to 50 dB is a quiet office; above 55 dB on high is a conversation-level fan. Size the unit so a quiet setting is enough for your room.
Decibels in everyday terms
| Level | Sounds like |
|---|---|
| 20-30 dB | Whisper, rustling leaves; fine for sleep |
| 30-40 dB | Quiet library |
| 40-50 dB | Quiet office, light rain |
| 50-60 dB | Normal conversation, a fan on high |
| 60+ dB | Busy restaurant |
Decibels are logarithmic: every 10 dB is perceived as roughly twice as loud.
Choosing for a bedroom
- Compare low-setting decibels, then check the CADR at that setting if the maker gives it.
- A larger unit on low is usually quieter than a small one on high for the same cleaning.
- Sleep or night modes often dim lights and cap the fan speed.
Products mentioned
Questions readers ask
How many dB is quiet for sleeping?
Under about 30 to 35 dB is quiet enough for most people.
Why is my purifier loud?
It may be on a high setting, undersized for the room, or the filter may be clogged.