Sones aren’t measured directly with a single device the way decibels are. Instead, sones are calculated from sound pressure or sound power measurements using a specific formula and, in professional settings, standardized lab procedures. For most people, the practical path is to measure sound in decibels and then convert to sones using a logarithmic formula.
What a Sone Actually Represents
A sone is a unit of perceived loudness, not raw sound intensity. One sone equals the loudness of a 1,000-hertz tone played at 40 decibels above the minimum audible threshold. That works out to roughly the quiet hum of a refrigerator in a calm room. The scale is designed to be intuitive: two sones sounds twice as loud as one sone, three sones sounds three times as loud, and so on. This makes sones far more useful for comparing how loud things actually feel to human ears than decibels, which use a logarithmic scale that doesn’t map neatly to perception.
Sones vs. Decibels
Decibels measure physical sound pressure. Sones measure how loud that sound pressure feels to a person. The two scales relate through a logarithmic formula:
dBA = 33.2 × log₁₀(sones) + 28
This means 1 sone corresponds to about 28 dBA (the sound pressure level at a distance of roughly 5 feet), 2 sones to about 38 dBA, 4 sones to about 48 dBA, and 8 sones to about 58 dBA. Every time the sone value doubles, the decibel reading increases by roughly 10 dBA. That 10-decibel jump is what the average person perceives as “twice as loud,” which is exactly why the sone scale exists: it tracks human hearing rather than physics.
One important caveat from the City of Seattle’s acoustic reference charts: there is no single exact formula to convert sones to sound power or sound pressure that works perfectly in all conditions. Published conversion values are approximations with a margin of error around plus or minus 2 dB.
How to Measure Sones at Home
You won’t find a consumer device that reads directly in sones. Here’s the practical approach:
First, measure the sound level in decibels using a sound level meter. You can buy a handheld meter for under $50, or use a smartphone app. The NIOSH Sound Level Meter app, developed by the CDC’s National Institute for Occupational Safety and Health, meets the Type 2 requirements of the international sound level meter standard when paired with a calibrated external microphone. It’s free and reliable enough for home use, though readings from a phone’s built-in microphone will be less precise than those from a dedicated external mic.
Position the meter at the distance where you’d normally be from the sound source. For a bathroom fan or range hood, that’s typically 3 to 5 feet. Take readings with the meter set to A-weighting (dBA), which filters sound the way human ears do. Let the reading stabilize for at least 10 seconds and note the average.
Then convert your dBA reading to sones. Rearranging the formula above gives you:
Sones = 10^((dBA − 28) / 33.2)
So if your range hood measures 55 dBA at 5 feet, that’s roughly 10^((55 − 28) / 33.2) = 10^(0.813) ≈ 6.5 sones. Keep in mind this is an estimate. Room acoustics, background noise, and microphone quality all introduce error. Your result will land in the right ballpark but won’t match a lab rating exactly.
How Manufacturers Test for Sone Ratings
The sone ratings printed on bathroom fans, range hoods, and other ventilation products come from controlled laboratory testing, not quick field measurements. The Home Ventilating Institute (HVI) publishes a standardized procedure called HVI Publication 915, most recently updated in March 2025. Products tested under this procedure earn HVI-certified ratings that appear on packaging and spec sheets.
The lab setup involves a specially constructed test chamber designed to eliminate reflections and background noise. Technicians measure sound pressure and sound power levels across multiple frequency bands, then calculate loudness in sones using the standardized method described in ISO 532-1:2017. This international standard, based on the Zwicker algorithm, builds a “specific loudness pattern” from frequency data and accounts for how the human ear processes different pitches at different volumes. It works for both steady sounds (like a fan running at constant speed) and time-varying sounds (like a fan cycling between speeds).
This is why your home measurement won’t perfectly match the rated sones on a product label. The lab controls for room size, ambient noise, distance, and microphone placement in ways that are impossible to replicate in a kitchen or bathroom.
Sone Ratings for Common Appliances
Knowing the scale helps you shop smarter for fans and hoods. Here’s what different sone levels feel like in practice:
- 1 to 2 sones (roughly 28 to 38 dBA): Very quiet. Comparable to a refrigerator humming or soft background music. You can hold a conversation at normal volume without raising your voice. This is the sweet spot for bathroom exhaust fans you plan to run overnight.
- 3 to 4 sones (roughly 44 to 48 dBA): Comfortable. Similar to a conversation happening in the next room. Most experts recommend 4 sones or less for a range hood at its normal working speed.
- 5 to 7 sones (roughly 51 to 56 dBA): Noticeably loud. Tolerable for short cooking sessions but enough to make you raise your voice. Typical of many standard range hoods on their highest setting.
- 8+ sones (roughly 58+ dBA): Loud. Comparable to busy traffic noise or someone speaking loudly right next to you. Some powerful commercial-style range hoods reach 10 to 13 sones at maximum speed.
Why the Conversion Isn’t Perfect
The formula above assumes a simple, steady tone. Real-world sounds are more complex. A bathroom fan produces noise spread across many frequencies, and human ears are more sensitive to some frequencies than others. A 40 dB tone at 1,000 Hz sounds louder than a 40 dB tone at 200 Hz, even though both measure the same decibel level. The ISO 532-1 standard handles this by analyzing loudness across the full frequency spectrum and weighting each band according to how human hearing actually works. A single dBA reading collapses all that detail into one number, which is why the home method gives you an approximation rather than a precise sone value.
For shopping decisions, the approximation is good enough. If you measure your current bathroom fan at roughly 6 sones and want something quieter, look for a replacement rated at 1 to 2 sones. You’ll notice the difference immediately. For precise acoustic work, like noise compliance testing or product certification, the full ISO 532-1 calculation using frequency-band data and specialized software is the only reliable path.