Sones vs decibels comes down to scale: a sone figure doubles when perceived loudness doubles, and a decibel figure climbs logarithmically. Most appliance noise is rated in decibels, but bathroom exhaust fans and range hoods are rated in sones, a unit most people have never met. This page explains what a sone is, using the certifying body's own definitions, and counts how makers in our catalog publish them.
What is a sone?
A sone is a unit of loudness. The Home Ventilating Institute, HVI, defines it as an internationally recognized unit of loudness, and describes the scale as linear, like inches. HVI certifies the airflow and sound ratings of residential ventilation products.
In technical terms, HVI says, one sone is equal in loudness to a pure tone of 1,000 cycles per second at 40 decibels above the listener's threshold of hearing. In everyday terms, it is equivalent to the sound of a quiet refrigerator.
HVI also gives a rough ladder for bathroom fans:
- 0.5 sone: the sound of rustling leaves.
- 1.0 sone: the sound of a refrigerator.
- 3.0 sones: typical office noise.
- 4.0 sones: a television at normal volume.
Is 2 sones twice as loud as 1 sone?
Yes, 2 sones is twice as loud as 1 sone, because sones scale the way you hear. HVI puts it in one line: double the sone value is double the loudness. A fan rated at 3 sones makes half the sound of one rated at 6.
Decibels do not behave like that. They follow a logarithmic scale, and it takes an increase of about 10 decibels to sound twice as loud, according to the National Park Service.
A shopper looking at 50 and 53 dBA has to know that. A shopper looking at 1.0 and 2.0 sones does not. The second fan is twice as loud, and that is all there is to it.
Panasonic's own table for the WhisperFit DC shows the scale at work. On a 4-inch duct at 0.25 inch of pressure, it lists 0.4 sone at 50 CFM, 0.8 at 80 and 1.2 at 110. By HVI's rule, the top setting is three times as loud as the bottom one, and twice as loud as the middle.
HVI describes the relationship this way: sones translate laboratory decibel readings into numbers that correspond to the way people sense loudness. The decibel readings come first, in the lab. The sone rating is what is worked out from them. Our guide to dBA covers the decibel side.
Can you convert sones to decibels?
No, not by any official method, so we never do. You will find charts online that offer an exact decibel equivalent for each sone value. We do not use them, for three reasons.
First, HVI publishes no such table. The body that defines and certifies the ratings does not offer a conversion.
Second, the translation runs one way. HVI says sones are worked out from laboratory decibel readings so that they correspond to the way people sense loudness. It gives no method for turning a sone rating back into a single decibel figure, and no maker we read gives one either.
Third, we do not need to. Every certified fan and hood is rated in sones, so they can be compared with each other directly. The only reason to convert is to compare a range hood with a dishwasher, and that comparison tells you little.
Dishwashers are rated in decibels, and our dishwasher guide compares them with each other in that unit. For the same reason, our decibel chart leaves sone ratings out and sets only decibel figures beside everyday sounds.
Which sone rating are you reading?
A sone rating is only as useful as the conditions behind it. Two details catch buyers out.
Bathroom fans: the test pressure
Box sone ratings come from a test at 0.1 inch of water, a low static pressure that stands for a short, easy duct run.
In a house, longer ducts and elbows add resistance, and the harder a fan has to push, the louder it gets. Some makers also publish a rating at 0.25 inch.
In our bathroom exhaust fan guide, one fan that is rated under 0.3 sone on the box is rated at 0.9 sone at the higher pressure. We rank on the tougher figure wherever a maker publishes it.
Our guide to fan and light combos ranks on that figure too, and there the Panasonic WhisperGreen Select with light holds a 0.3 sone certification moving 110 CFM through a 6-inch duct at 0.25 inch.
Duct size moves the number as much as pressure does. At 0.25 inch and its 110 CFM setting, Panasonic rates the plain WhisperGreen Select 0.3 sone through 6-inch ducting and 0.8 sone through 4-inch ducting. On HVI's linear scale, the narrower duct makes the same fan about 2.7 times as loud.
Range hoods: the speed
Range hood makers usually headline the sone figure from the slowest speed. For ENERGY STAR, hood noise is measured at working speed, which it defines as the first speed reaching 100 CFM or more, so each maker ends up with a sanctioned low-speed number to advertise.
At full speed, the quiet-marketed hoods in our range hood guide were certified at 5 to 13 sones. Find the rating for the speed you will cook at.
FOTILE publishes every speed for its EMG9050, and HVI certifies all four: 0.6 sone at 283 CFM on low, 3.5 at 450, 6 at 617 and 7.5 at 695 on boost. Because sones scale with loudness, boost is about 12 times as loud as low. A box that printed only the 0.6 would hide all of that.
Where the kitchen shares its space with the living area, our range hood guide's open-plan section compares sones at every speed the makers list.
How many fans and hoods publish a realistic sone rating?
Most bathroom fans in our catalog publish a sone rating at the tougher 0.25 inch pressure, and most range hoods carry HVI certification, but the gaps are worth knowing. These tallies cover the models we list as of October 26, 2026; the wider market may differ.
| Catalog | Products | What we counted | Count |
|---|---|---|---|
| Bathroom exhaust fans | 55 | Maker publishes a sone figure at 0.25 inch | 45 |
| Range hoods and inserts | 63 | HVI-certified sone ratings | 50 |
| Range hoods and inserts | 63 | Not found in HVI's directory | 13 |
| Inline duct fans | 18 | Rated in sones rather than decibels | 3 |
We read each product's spec sheet wording, submittal and HVI listing as recorded in the catalog before counting it.
Bathroom fans without a 0.25 inch figure
Ten of the 55 fans give a sone figure only at 0.1 inch, or give no pressure at all. Several Broan spec sheets list the airflow at 0.25 inch and leave the sone cell empty.
Broan's sheet for the Flex Series AE110 shows how much that hides. It gives 1.0 sone at 110 CFM at 0.1 inch and 92 CFM at 0.25 inch with no sone figure. HVI's directory fills the gap: 1.5 sones at 92 CFM at 0.25 inch, half again as loud.
Our Broan sone ratings page lists which Broan models carry a figure at each pressure.
Range hoods: spec sheet range against HVI's high speed
Zephyr prints a sone range on its own spec sheets, such as "Sones (Min. - Max.) 1.8 - 3.5" for the Breeze I. HVI certifies the same hood at 9 sones at 230 CFM on high speed, vertical. The spec sheet range does not say which speed each end belongs to.
Of the 17 Zephyr hoods and inserts in our catalog with both a spec sheet range and an HVI high-speed rating, 14 have a spec sheet maximum below HVI's figure, 2 match it, and 1, the Valina, sits above it. Our Zephyr sone ratings page sets each pair side by side.
Duct fans: mostly decibels
Inline duct fans sit between the two worlds. Of the 18 in our catalog, only the 3 Vents-US TT models give sones, with high and low speed figures. AC Infinity, VIVOSUN, TerraBloom and iPower print dBA or dB.
Is a sone rating certified or self-reported?
Check HVI's directory: a certified rating comes from HVI's independent testing, and a brand that does not take part reports its own figure.
HVI tests products independently, and its certified ratings are listed in a public directory. HVI says range hoods have sone ratings too, and that they can be found in that directory.
Not every brand takes part. HVI's directory leaves out several direct-to-consumer range hood brands, which means the sone figures they print are self-reported. In our range hood research, one such brand gave two different figures for the same hood in two places. A certified rating is the one to trust.
ENERGY STAR uses sones as well. Its ventilation fan criteria set maximum allowable sound levels in sones, along with minimum efficiency, and a qualifying fan must still deliver a set share of its rated airflow once the test pressure rises to 0.25 inch.
Other ventilation products use sones too. In our inline duct fan guide, only one maker publishes what its fan sounds like on low speed as well as high.
Few ERV and HRV makers publish a noise figure at all, and our ERV and HRV guide lists the sone ratings we could verify alongside sound power tables.
How do you use sone ratings when shopping?
Sone ratings are easy to use once you hold every product to the same pressure, speed and duct. These steps follow the order we use in our guides.
- Compare sones only with sones, and never convert them to decibels.
- For a bathroom fan, start from HVI's quiet threshold of 1.0 sone or less.
- Find the rating at 0.25 inch of pressure, which is closer to a real installation than 0.1 inch.
- Match the duct size in the table to the duct you have, since 4-inch ratings run higher than 6-inch.
- For a range hood, skip the lowest-speed figure and read the rating at full speed or at the airflow you need.
- Check the model in HVI's directory and prefer a certified rating to one found only on the maker's site.
A lower sone number is quieter in direct proportion, so a 0.6 sone fan is half as loud as a 1.2 sone fan at the same pressure and duct.
