What a decibel actually measures
A generator decibel rating is not a simple unit like pounds or gallons. It describes sound pressure on a logarithmic scale, which means small changes in the number represent large changes in the physical pressure your ear receives. The Occupational Safety and Health Administration (OSHA) explains in its Technical Manual that sound is a rapid variation of atmospheric pressure caused by some disturbance of the air, which travels as a wave of pressure changes that the ear perceives as sound.
OSHA sets the reference sound pressure at 20 micropascals at 1,000 Hz, which is defined as 0 dB. That is the standardized threshold of hearing for a young person with undamaged hearing. At the upper end of the range relevant to human hearing, the threshold of pain occurs at about 140 dB. According to OSHA, the sound pressure at that point is roughly 10 million times greater than the threshold of hearing. Because the range is so wide, a logarithmic decibel scale compresses those values into a manageable set of numbers.
One practical consequence is that you cannot add decibel values the way you add ordinary numbers. OSHA states that decibels are logarithmic values, so it is not correct to sum multiple sound values using arithmetic addition. Two generators each rated at 70 dBA do not produce 140 dBA together; OSHA notes that, as a general rule, doubling the sound power increases the noise level by 3 dB.
Why dBA matters more than plain dB
Human ears do not respond equally to all frequencies. A low rumble and a high whine at the same physical sound pressure do not sound equally loud. To account for this, sound level meters apply weighting networks. According to OSHA, weighting methods such as the A-weighted network are intended to indicate perceived loudness across frequency bands and to provide a rating that reflects the impact noise has on human hearing.
Generac’s white paper on sound measurements says A-weighting has become the standard weighting network applied to most acoustic measurements seen by consumers. When a measurement has been A-weighted, the result is written as dBA or dB(A). That is the figure you normally see on a generator specification sheet. A dBC or unweighted figure would tell you more about low-frequency energy, but dBA is the common reference for comparing generator noise because it approximates how people perceive loudness.
OSHA also notes that for the same sound pressure level, high-frequency noise is much more disturbing and more capable of producing hearing loss than low-frequency noise. OSHA adds that the A-network attenuates very low frequencies quite severely, while the C-network hardly attenuates them, so a dBA figure says little about low-frequency rumble.
Reference points from OSHA’s decibel scale
OSHA’s Technical Manual includes a decibel scale with typical sound levels. These reference points help put a generator rating in context. At the quiet end, 0 dB is the threshold of hearing, 20 dB is a silent study room, and 40 dB is a soft whisper from about 5 feet away. A normal conversation at 3 feet is about 60 dB, and classroom chatter is around 70 dB.
Moving up the scale, OSHA lists a freight train at 100 feet as about 80 dB, a boiler room as 90 dB, and a construction site as 100 dB. A night club with music is around 110 dB, operating heavy equipment is about 120 dB, and a jet taking off at 200 feet is about 130 dB. The threshold of pain sits at 140 dB. These are workplace-oriented examples from OSHA, but they give a useful frame for reading a home generator specification.
What a generator decibel rating actually states
A generator rating is a measurement taken under controlled conditions, not a promise about what you will hear in your yard. According to Generac, product sound pressure levels are measured in idealized, repeatable conditions. For most generator products, the de facto standard distance is 7 meters, or about 23 feet. The unit is placed in an open area, and measurements are taken at fixed points around it.
Generac states that no manufacturer can predict or publish a promised on-site sound pressure level. The sound pressure levels measured by installers, specifying engineers, or municipal inspectors are the cumulative result of the generator, ambient noise, and reflective surfaces or buildings around the generator. A concrete wall, a shed, a fence, or even hard ground can reflect sound and change the reading at your ear.
Generac also explains a useful rule for estimating distance effects. In a free field, doubling the distance from a point source reduces the sound pressure level by about 6 dB. If a generator is measured at 70 dBA at 7 meters, the predicted level at 14 meters is about 64 dBA. Moving closer increases the level. The same white paper gives an example where moving from 7 meters to 3 meters predicts an increase of 7 dBA. This is a rough estimate, because real sites rarely behave like a free field.
A published rating applies to the model it was measured on, under the conditions stated. Always check the documentation for your own generator and follow the manufacturer’s instructions for placement and operation.
How much a decibel change matters
Because the decibel scale is logarithmic, a change of a few decibels is more significant than it first appears. The Federal Highway Administration (FHWA) offers a useful comparison in its discussion of highway noise barriers. Effective noise barriers typically reduce noise levels by 5 to 10 decibels, and the FHWA says that cuts the loudness of traffic noise by as much as one half. A barrier that achieves a 10 dB reduction can reduce the sound level of a typical tractor trailer pass-by to that of an automobile.
That comparison is helpful when reading generator specifications. A generator rated at 60 dBA is not just slightly quieter than one rated at 70 dBA. Going by the FHWA’s description, a 10 dB difference can mean the quieter unit sounds as much as half as loud. Small numeric differences on a spec sheet can therefore represent a meaningful change in how intrusive a generator feels at a campsite, job site, or backyard.
The FHWA also notes that a barrier must be tall enough to break the line of sight from the noise source to the receiver to achieve a 5 dB reduction. After that, each additional meter of barrier height can add about 1.5 dB of reduction. This is highway-specific guidance, but it explains why simply placing a small object near a generator does not create a large drop in sound. The path between the generator and your ear matters.
Hearing risk context
The National Institute on Deafness and Other Communication Disorders (NIDCD) explains that sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure. Long or repeated exposure to sounds at or above 85 dBA can cause hearing loss. The louder the sound, the shorter the amount of time it takes for noise-induced hearing loss to occur.
NIDCD lists normal conversation at 60 to 70 dBA. The level at your ear depends on how close you stand and how long you stay there. NIDCD says your distance from the source and the length of time you are exposed are important factors in protecting your hearing. A good rule of thumb from NIDCD is to avoid noises that are too loud, too close, or last too long.
Noise-induced hearing loss can be immediate or gradual, temporary or permanent, and it can affect one ear or both ears. NIDCD states that most noise-induced hearing loss is caused by damage and eventual death of hair cells in the inner ear. Unlike bird and amphibian hair cells, human hair cells do not grow back. Loud noise exposure can also cause tinnitus, a ringing, buzzing, or roaring in the ears or head. This information is general health context, not medical advice. If you have concerns about your hearing, consult a qualified health professional.
Key terms at a glance
| Term | What it means |
|---|---|
| dB | Decibel, a logarithmic unit of sound pressure level |
| dBA | A-weighted decibels, adjusted to approximate human hearing |
| Sound pressure level | The pressure variation measured at a microphone or ear |
| Sound power | The total acoustic energy a source emits, independent of environment |
| Free field | A space with no reflected sound waves |
| Reverberant field | A space where reflected sound dominates |
| Threshold of hearing | The quietest sound a young person with undamaged hearing can typically hear, set at 0 dB |
| Threshold of pain | About 140 dB, where sound pressure causes pain |
Applying this to your generator
When you compare generator decibel ratings, check that the numbers use the same weighting and the same distance. A dBA figure at 7 meters is the common convention, but a figure taken at a different distance or with a different weighting is not directly comparable. Generac’s white paper notes that measurements have a suffix such as dBA or dB(A) to show the weighting, and the standard distance for most generator products is 7 meters.
Remember that the rating is a starting point, not a site prediction. Reflective surfaces, ambient noise, and the direction of the exhaust all change what you hear. For more on how generator sound behaves in real spaces, see our guide to how generator sound works and the section on factors affecting noise. If you want to understand how ratings are taken, read about measuring generator noise.
Carbon monoxide safety must come first when you think about noise. Never enclose a running generator, block its airflow, or modify the exhaust or muffler. Only manufacturer-approved accessories should touch exhaust or cooling parts. If you want to reduce noise, start with safe placement and distance rather than enclosures. Our guides to placement and distance and sound barriers explain options that do not compromise safety.
For a broader look at this topic, visit the parent section on generator noise basics and the pillar article on generator noise levels explained. The decibel levels category page also collects related guidance.
Frequently asked questions
Is a generator rated at 60 dBA twice as quiet as one rated at 70 dBA?
Perceived loudness does not work on a simple linear scale. The Federal Highway Administration says a reduction of 10 dB cuts the loudness of traffic noise by as much as one half. By that description, a 60 dBA generator could sound as much as half as loud as a 70 dBA unit, if both figures were measured at the same distance and under the same conditions.
Why does my generator sound louder at home than its rating suggests?
According to Generac, no manufacturer can promise an on-site sound pressure level. The rating is measured in an open area at a fixed distance, usually 7 meters. At your site, walls, fences, hard ground, and ambient noise all combine with the generator’s output, so the measured level can be higher than the specification.
Does doubling the distance from a generator really cut the noise in half?
Doubling the distance reduces the sound pressure level by about 6 dB in a free field, according to both OSHA (which describes it on an unweighted scale) and Generac. That is a noticeable reduction, but it is not the same as cutting perceived loudness in half. The FHWA’s guidance suggests a 10 dB reduction is closer to a halving of perceived loudness.
For more background on decibel levels and how they apply to generators, see the decibel levels category page.
