Sones vs. Decibels: Two Noise Scales, One Confusing Mess
You’re shopping for a range hood. The noise spec says 6 sones. You’re shopping for a dishwasher. The noise spec says 44 dB. You cannot compare these numbers without converting, and even then, the comparison is imperfect. Here’s the full story.
What decibels actually measure
Decibels (dB) measure sound pressure level — a physical quantity. A microphone captures pressure waves, the meter computes the level, and out comes a number. It’s objective, repeatable, and completely unintuitive for humans.
The scale is logarithmic. Every 10 dB increase sounds roughly twice as loud to human ears, but represents a 10x increase in acoustic power. A 50 dB dishwasher sounds about twice as loud as a 40 dB model, not 25% louder as the numbers might suggest. This trips up nearly everyone who hasn’t studied acoustics.
Most appliance specs use dBA — A-weighted decibels — which filters the measurement to match human hearing sensitivity. We hear mid-frequencies (1–4 kHz) much better than low bass or extreme highs, and A-weighting accounts for this. When a dishwasher says 44 dB, it almost always means 44 dBA.
What sones actually measure
Sones measure perceived loudness — a psychoacoustic quantity. The scale was developed by Stanley Smith Stevens at Harvard in the 1930s, based on experiments where listeners judged how loud different sounds seemed. It maps directly to how humans experience volume.
The key property: the scale is linear. 2 sones is twice as loud as 1 sone. 4 sones is twice as loud as 2 sones. No logarithms, no mental math. This makes sones genuinely more useful for comparing products — you can look at two numbers and immediately know the loudness relationship.
The reference point: 1 sone equals the loudness of a 1 kHz tone at 40 dB SPL. From there, every doubling in sones corresponds to roughly a 10 dB increase.
The conversion
The relationship between sones and dBA isn’t a clean formula because they measure different things (physical pressure vs. perceived loudness), but the standard approximation works well enough for appliance shopping:
dBA ≈ 33.2 × log₁₀(sones) + 28
Or working backwards: sones ≈ 10^((dBA − 28) / 33.2)
Here’s what that looks like with real product examples:
| Sones | ~dBA | What it sounds like | Real example |
|---|---|---|---|
| 0.3 | 18 | Near-silent, barely perceptible | Broan QTXE080 bath fan (0.3 sones) |
| 0.5 | 21 | Faint hum, noticeable only in dead silence | Panasonic WhisperCeiling (0.3–0.5 sones) |
| 1.0 | 28 | Quiet room ambiance — a refrigerator from 3 meters | Broan InVent (1.0 sone) |
| 2.0 | 37 | Quiet office, gentle background presence | Delta BreezSlim (2.0 sones) |
| 4.0 | 48 | Normal conversation level, clearly audible | Mid-range range hood at medium speed |
| 6.0 | 54 | Loud enough to talk over | Typical range hood at high speed |
| 8.0 | 57 | Annoying in sustained use | Powerful range hood on boost |
| 12.0 | 64 | Loud — you’ll raise your voice | High-CFM commercial-style range hood |
These conversions are approximate. The formula works best between 1 and 10 sones. Below 0.5 sones, psychoacoustic models get squirrelly, and the conversion becomes less reliable.
Why different appliances use different scales
This isn’t random. It’s the result of industry standards that developed independently.
Bathroom exhaust fans use sones because the Home Ventilating Institute (HVI) adopted sones as the standard rating for ventilation products decades ago. HVI testing uses a specific procedure (HVI 916) in a standardized test room. Every certified fan gets a sones rating under comparable conditions. This makes the numbers genuinely comparable across brands — unusual for appliance noise specs.
Range hoods also use sones, again because of HVI certification. The testing procedure accounts for multiple speed settings, so a range hood might be rated at 1.5 sones on low and 8 sones on high.
Dishwashers, washing machines, refrigerators, and most other appliances use dBA because their industry groups and regulatory bodies settled on decibel-based standards. The EU energy label requires dB(A) re 1 pW (decibels referenced to 1 picowatt of sound power). US manufacturers followed suit because that’s what the test standards already measured.
Nobody sat down and decided this split made sense. It doesn’t. It’s the residue of different standards bodies making independent choices in different decades.
Which scale is more useful?
Sones, and it’s not close. A linear scale that maps directly to perceived loudness is objectively better for comparing products. If bathroom fan A is rated 1.0 sone and fan B is rated 2.0 sones, fan B is twice as loud. Done. No logarithmic conversion needed.
With decibels, the same comparison requires you to know that a 10 dB difference means roughly a doubling of perceived loudness, that a 3 dB difference is barely perceptible, and that the relationship isn’t proportional to the raw numbers. Most consumers don’t know this, so they wildly overestimate or underestimate differences when shopping by dB.
The reason dBA dominates is inertia and measurement convenience. Decibels are what microphones and meters output natively. Sones require a psychoacoustic model to compute. For engineers and test labs, dB is the natural unit. For consumers, sones would be better — but the consumer-facing convention is set, and dishwashers aren’t switching to sones anytime soon.
Practical rules for shopping
Comparing within the same scale: Just compare the numbers. Lower is quieter. A 42 dBA dishwasher is meaningfully quieter than a 48 dBA one — that 6 dB difference is about 50% louder in perceived terms. A 1.0 sone bath fan is half as loud as a 2.0 sone fan.
Comparing across scales: Convert using the formula above or the table. A range hood at 4 sones (~48 dBA) and a dishwasher at 48 dBA are in the same loudness ballpark, though direct comparison is imperfect because the frequency content differs.
Minimum thresholds for “quiet”:
- Bath fans: below 1.0 sone is genuinely quiet. Below 0.5 sones, you likely won’t hear it over ambient room noise.
- Range hoods: below 3 sones on the speed setting you’ll actually use. Marketing loves to advertise the lowest speed, but nobody runs a range hood on low while searing a steak.
- Dishwashers: below 44 dBA is quiet. Below 40 dBA, you’ll struggle to hear it from the next room.
Ignore the extremes. A bath fan rated at 0.3 sones sounds almost identical to one at 0.4 sones — you’re below the threshold of reliable human perception in a normal home environment. Don’t pay a $50 premium for a difference you can’t hear.
The missing standard
What the industry actually needs is a single loudness scale — ideally sones — used consistently across all appliance categories, measured under standardized and independently verified conditions. That doesn’t exist. Until it does, you’re stuck converting between scales, guessing at test conditions, and trusting manufacturer claims that may or may not reflect your real-world experience.
That’s why dBSkeptic combines spec data with real-world buyer reports rather than treating manufacturer numbers as gospel. The specs give us a starting point. Real-world experience fills in what they miss. See how we evaluate noise for details.
For more on what different dB levels sound and feel like in practice, see the decibel chart.