Every guide on this site ranks products by a noise figure, and almost all of those figures are in decibels. This page explains what the number means, what it leaves out, and how to read it the way we do. We do not measure anything ourselves. Every statement here comes from a standards body, a government agency or a manufacturer, and we say which.
What a decibel is
The decibel, written dB, is the unit used to measure the intensity of a sound. The scale is not like a ruler. OSHA's technical manual explains that decibels are measured on a logarithmic scale, so a small change in the number of decibels indicates a huge change in the amount of sound pressure. The scale exists because the ear hears an enormous range of pressures, and a logarithmic scale squeezes that range into manageable numbers.
Zero decibels is not silence. By definition, OSHA says, 0 dB is set at a reference sound pressure. That is worth remembering when a product is advertised at "0 dB", as some fanless heaters and absorption fridges are. It is a description, not a reading.
What the A in dBA means
People do not hear all pitches equally. The FAA puts it simply: we are less able to hear low frequencies like the rumble of thunder, but hear high frequencies like the cry of a baby more strongly.
A-weighting adjusts a measurement to match that. The FAA says the A-weighted scale most closely approximates the relative loudness of sounds in air as perceived by the human ear. A figure in dBA, sometimes written dB(A), has had that adjustment applied.
When a maker writes plain dB, you do not know whether the figure was weighted. In our guides we print the unit exactly as the maker wrote it, and we do not treat dB and dBA as the same thing.
The two numbers worth remembering: 3 and 10
Three decibels is a doubling of sound power. OSHA states it as a general rule: doubling the sound power increases the noise level by 3 dB. By that rule, two identical fans running side by side are about 3 dB louder than one.
Ten decibels sounds about twice as loud. The National Park Service explains that an increase of 10 dB causes a doubling of perceived loudness, and represents a ten-fold increase in sound level. In its words, if one vacuum cleaner measures 70 dB, then 80 dB would be the equivalent of ten vacuum cleaners.
Put together, these tell you how to weigh a difference. A 10 dB gap between two dishwashers is large: one sounds half as loud as the other. A 2 dB gap is small, and if the two figures come from different makers, it may be no gap at all.
Distance changes everything, and makers rarely state it
Sound fades as you move away from its source. OSHA gives the rule for open space: the sound pressure level decreases 6 dB each time the distance from a point source is doubled.
Two things follow. First, a figure with no distance attached is incomplete. Almost none of the appliance makers we read state one. Portable generators are the exception, and even there the distances differ: one maker measures from 23 feet and another from 22.
Second, a room is not open space. OSHA notes that where sound reflects off surfaces, the level decreases by less than 6 dB each time the distance doubles. So the figure a maker measured, in whatever space it used, is not the figure you will hear in a furnished room.
Why the figure on the box flatters the product
We have now read the noise claims for more than 170 products. The pattern is consistent: when a maker gives one figure, it is the quietest one available.
- Lowest speed. Tower fan, portable air conditioner and heater makers often quote an "as low as" figure. Dreo footnotes one of its figures as tested at the lowest speed setting.
- Quiet mode. Robot vacuum figures usually describe quiet mode. One maker publishes all four modes for a robot, and they run from 59 dB to 70 dB.
- Light load. Honda lists its EU2200i generator at 48 dB(A) at quarter load and 57 at rated load.
- The gentle half of the cycle. Bosch lists a compact washer at 52 dBA washing and 72 dBA spinning. A single "quiet" figure for a washer probably describes the wash.
None of these figures is false. Each describes a real moment in the product's life. The question to ask is whether it is the moment you care about.
The makers that publish both ends deserve credit, and our guides rank them above makers that publish one flattering number. You can see this at work in the guides to portable air conditioners, generators and washing machines.
Some reference points
The US National Institute on Deafness and Other Communication Disorders gives these everyday levels: whispering at 30 dB, a humming refrigerator at 40 dB, and normal conversation at 60 to 70 dBA. The National Park Service notes that some remote park trails measure around 20 dBA, softer than a whisper.
Use these as a rough scale only. A maker's 40 dB and a refrigerator's 40 dB were not measured the same way or from the same distance.
How to read a noise figure, in five questions
- Which setting does it describe? Lowest speed, quiet mode, quarter load, or the wash cycle. If the maker does not say, assume the quietest.
- Is there a figure for the loud end? A maker that publishes both ends is telling you more than one that publishes the floor.
- What is the unit? dBA and plain dB are not interchangeable. Bathroom fans and range hoods use sones, which work differently. See sones vs decibels.
- Is a distance stated? Usually not. Without one, compare the figure with others from the same maker, and be careful across brands.
- How big is the gap? Ten decibels is twice as loud. Two or three decibels between different brands is within the noise of how they measure.
Common questions
What is the difference between dB and dBA?
dB is the plain decibel. dBA is a decibel figure that has been A-weighted, which means it gives less weight to the low and very high pitches people hear less well. The FAA says the A-weighted scale most closely approximates the relative loudness of sounds as perceived by the human ear. A maker that writes dB without the A has not told you which it used.
How much louder is 10 decibels?
About twice as loud to the ear. The National Park Service puts it this way: an increase of 10 dB causes a doubling of perceived loudness and represents a ten-fold increase in sound level. So a 60 dBA dishwasher sounds roughly twice as loud as a 50 dBA one.
Is a 3 decibel difference worth paying for?
It is real but modest. OSHA notes that doubling the sound power raises the level by 3 dB, so 3 dB is a meaningful engineering gain. To the ear it is a small step, far short of the 10 dB that sounds twice as loud. And when two makers measure in different ways, a 3 dB gap between brands may not exist at all.
Why does my appliance sound louder than its rating?
Usually for three reasons. The rating often describes the quietest setting. Makers rarely state the distance they measured from. And rooms reflect sound: OSHA notes that indoors, sound falls off by less than the 6 dB per doubling of distance you get in open space.
Can I compare decibel figures between brands?
Only with care. Compare figures that describe the same setting, and treat small gaps as unknown. Within one brand, where the method is likely the same, the comparison is safer. Our guides say which setting each published figure describes, whenever the maker tells us.
