Decibel Shield
Sones to decibels converter
One sone is as loud as a 1 kHz tone at 40 dB, and every doubling of sones adds 10: 2 sones is 50 phons, 4 sones is 60. Below 1 sone the scale bends, so 0.3 sones is about 26 phons. A phon equals a decibel only for a 1 kHz tone, so a fan's sone rating is a guide to loudness, not an exact dB(A) reading. Enter sones or phons and the other updates.
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1.5 sones is as loud as a 1 kHz tone at
45.9 dB SPL
That is 45.9 phons. A fan with this rating will not read exactly that on a dB(A) meter.
Above 1 sone (40 phons) every doubling of sones adds 10 phons. Below it the converter uses the relation in ISO 532-1's reference program.
Sones to phons table
| Sones | Phons | Loudness against 1 sone |
|---|---|---|
| 0.3 | 26.3 | × 0.3 |
| 0.5 | 31.4 | × 0.5 |
| 0.8 | 37.0 | × 0.8 |
| 1 | 40.0 | × 1 |
| 1.5 | 45.8 | × 1.5 |
| 2 | 50.0 | × 2 |
| 2.5 | 53.2 | × 2.5 |
| 3 | 55.8 | × 3 |
| 4 | 60.0 | × 4 |
| 5 | 63.2 | × 5 |
| 6 | 65.8 | × 6 |
| 7 | 68.1 | × 7 |
| 8 | 70.0 | × 8 |
Sones, phons and decibels
A decibel (dB SPL) measures sound pressure. A phon is the level of a 1 kHz tone that sounds as loud as the sound being rated, so 60 phons sounds as loud as a 60 dB tone at 1 kHz. A sone turns phons into a scale that grows with what you hear: 1 sone is 40 phons, and loudness doubles for every 10 phons above that, so N = 2(L − 40)/10 and L = 40 + 10 × log2(N). Below 1 sone the converter uses the relation in ISO 532-1's reference program, L = 40 × (N + 0.0005)0.35.
Sources: ISO 532-1:2017, Methods for calculating loudness (sample); ISO 532-1 reference program; UNSW Physclips, dB: What is a decibel?; HyperPhysics, Phons and Sones; Home Ventilating Institute, FAQs; ENERGY STAR, Ventilating Fans Key Product Criteria; ASHRAE Interpretation IC 62.2-2007-1; PNNL Building America Solution Center, Bathroom Fan Ratings.
Sone ratings on fans and range hoods
Bathroom fans and range hoods sold in North America are rated in sones under the Home Ventilating Institute's test procedure (HVI 915). ENERGY STAR's limit is 2.0 sones for range hoods and for bathroom and utility fans up to 200 CFM, and 3.0 sones from 201 to 500 CFM. ASHRAE Standard 62.2 limits fans that run now and then, such as a bathroom fan, to 3 sones and fans that ventilate the whole home continuously to 1 sone. HVI says the lowest rating it currently certifies is under 0.3 sone.
To hear the difference yourself, measure the fan with the decibel meter from where you stand. The reading will be in dB(A), close to but not the same as the phon value above. The decibel chart puts it beside everyday sounds.
How many decibels is 1 sone?
One sone is the loudness of a sound with a loudness level of 40 phons, which is as loud as a 1 kHz tone at 40 dB SPL. For other sounds, and fans are other sounds, there is no exact figure in dB(A), because a phon matches a decibel only at 1 kHz.
What does a sone rating mean on a bathroom fan or range hood?
It is the fan's loudness measured in a lab under a standard test (HVI 915, which ENERGY STAR uses), in sones so that the numbers scale with what you hear: a 2-sone fan sounds about twice as loud as a 1-sone fan, and a 6-sone fan twice as loud as a 3-sone one. That is easier to compare than decibels, where twice as loud is roughly 10 dB more.
Why can a sones to dB converter only be approximate?
Sones measure how loud a sound seems, which depends on its frequencies; decibels measure its pressure. ISO 532-1 gives the example of a broadband sound that reads 68 dB(A) and has a loudness of 24 sones, which is 86 phons. The phon value here is the level of a 1 kHz tone that sounds equally loud, a fair guide to loudness but not a meter reading.
Is 1.5 sones quiet?
It is under the common limits: 1.5 sones is about 46 phons, half as loud again as a 1-sone fan, and below ENERGY STAR's 2.0-sone ceiling for bathroom fans up to 200 CFM and range hoods. The Home Ventilating Institute compares one sone to a quiet refrigerator.
