Sones to decibels: the conversion chart
Sones are a linear loudness scale: 2 sones genuinely sounds twice as loud as 1 sone. Decibels are logarithmic, which is why the conversion isn't a simple multiplication. The table below maps the sone ratings you'll see on bathroom fans and range hoods to approximate dBA values and everyday sounds.
| Sones | ≈ dBA | Sounds like |
|---|---|---|
| 0.3 | 23 | Threshold of a very quiet bedroom; effectively inaudible |
| 0.5 | 30 | Rustling leaves; a whisper at 2 meters |
| 0.7 | 35 | Very soft background hum |
| 1 | 40 | A quiet modern refrigerator in the next room |
| 1.5 | 46 | Soft rainfall on a roof |
| 2 | 50 | A quiet office; light traffic at a distance |
| 3 | 56 | A television at low volume |
| 4 | 60 | Normal conversation at 1 meter |
| 6 | 66 | A loud conversation; older bathroom fans |
| 8 | 70 | A vacuum cleaner at a distance |
Important caveats on the conversion
There is no exact sones↔dB formula: sones are measured with a loudness model (ISO 532) that accounts for how human hearing weighs different frequencies, while dBA applies a fixed frequency weighting. The figures above (and the ≈dBA values shown throughout QuietScore) use the standard approximation that 1 sone = 40 phon and loudness doubles per 10 phon. Treat them as a guide, accurate to within a few dB for typical fan noise. The sones figures themselves are exact certified lab measurements — when comparing two fans, always compare sones directly.
What's a good rating?
- ≤ 0.3 sones — effectively silent; you'll check whether the fan is on.
- ≤ 1.0 sone — quiet; unobtrusive in a small bathroom. Our bathroom fan rankings show hundreds of models at this level.
- 2–3 sones — clearly audible; typical of mid-range range hoods on working speed.
- 4+ sones — loud; common in older builder-grade fans, and the usual reason people go looking for a replacement.