How this is calculated
A generator in the open behaves as a point source, so the level falls by six decibels every time the distance doubles. The drop from 7 meters to any distance d is twenty times the base-ten logarithm of d divided by seven. Screening is subtracted after that.
Worked example. An open-frame set publishes 72 dB(A) at 7 m and the neighbor’s bedroom window is 30 m away with nothing solid between. Thirty divided by seven is 4.29, its logarithm is 0.632, and twenty times that is 12.6 dB. So 72 minus 12.6 leaves 59.4 dB(A) at the window.
Against a 40 dB(A) suburban night that is 19 dB over, which the ear reads as nearly four times as loud as the night itself. Getting the same machine to 40 dB(A) by distance alone would take 279 meters, which is why nobody solves this with lawn.
Quick answers
How loud is a generator at 7 meters?
Roughly 48–54 dB(A) for a suitcase inverter in eco mode, 68–76 for an open-frame gasoline set, 62–70 for an enclosed home standby.
How much does distance reduce generator noise?
Six decibels per doubling: 6.6 dB by 15 m, 12.6 dB by 30 m, 17.1 dB by 50 m, 23.1 dB by 100 m.
What is the difference between a 52 dB and a 68 dB generator?
Sixteen decibels, read as about three times as loud and carrying forty times the energy. At 30 m one is 39 dB(A) and the other 55.
Will a fence or a wall quiet my generator?
About 5 dB once it is solid, gap-free and tall enough to break the line of sight, then 1.5 dB per extra meter of height, with 10 dB the practical ceiling.
What are the quiet hours for generators in campgrounds?
Great Smoky Mountains posts generator quiet hours of 8:00 pm to 8:00 am against campground quiet hours of 10:00 pm to 6:00 am.
Is there a legal noise limit for a home generator?
Not a federal one in the United States; the binding number is municipal. In Europe the machine itself is capped and marked under Directive 2000/14/EC.
Decibels at 7 meters by generator class
Click a column heading to sort. The 7 m column is the published spread across spec sheets; the columns to its right carry that band’s midpoint outward by the inverse-square law.
| Class | Size band | At 7 m 23 ft |
At 15 m 49 ft |
At 30 m 98 ft |
At 50 m 164 ft |
Reads as |
|---|---|---|---|---|---|---|
| Suitcase inverter, quiet mode | 1–2.2 kW | 48–54 | 44 | 38 | 34 | A fridge in the next room |
| Suitcase inverter, rated load | 1–2.2 kW | 55–61 | 51 | 45 | 41 | Speech at arm’s length |
| Larger inverter set | 3–7 kW | 58–66 | 55 | 49 | 45 | A window air conditioner outside |
| Air-cooled home standby, enclosed | 8–26 kW | 62–70 | 59 | 53 | 49 | Central air that never cycles off |
| Liquid-cooled standby, enclosed | 25–60 kW | 63–72 | 61 | 55 | 50 | A heat pump working hard |
| Canopied mobile diesel | 20–100 kW | 60–72 | 59 | 53 | 49 | A parked truck idling |
| Open-frame gasoline, contractor style | 3–8 kW | 68–76 | 65 | 59 | 55 | A gas mower two gardens away |
| Large open-frame, job-site style | 8–15 kW | 72–80 | 69 | 63 | 59 | Curbside traffic |
| Open industrial diesel, no canopy | 20–100 kW | 80–90 | 78 | 72 | 68 | At the NIOSH 85 dBA eight-hour exposure limit even at 7 m |
Class bands, never a single model. Check which load your own plate figure was measured at: inverter sets quote eco mode first and rated load several decibels higher.
The distance table
The whole of the physics on one grid. Find your 7 meter figure down the left, read across.
| At 7 m (23 ft) | 15 m (49 ft) | 30 m (98 ft) | 50 m (164 ft) | 100 m (328 ft) | Drop from 7 m |
|---|---|---|---|---|---|
| 48 | 41.4 | 35.4 | 30.9 | 24.9 | — |
| 52 | 45.4 | 39.4 | 34.9 | 28.9 | — |
| 58 | 51.4 | 45.4 | 40.9 | 34.9 | — |
| 62 | 55.4 | 49.4 | 44.9 | 38.9 | — |
| 66 | 59.4 | 53.4 | 48.9 | 42.9 | — |
| 68 | 61.4 | 55.4 | 50.9 | 44.9 | — |
| 72 | 65.4 | 59.4 | 54.9 | 48.9 | — |
| 76 | 69.4 | 63.4 | 58.9 | 52.9 | — |
| 85 | 78.4 | 72.4 | 67.9 | 61.9 | — |
| Any level | −6.6 | −12.6 | −17.1 | −23.1 | −6 dB per doubling |
What 52 and 68 decibels actually feel like
The scale is not linear. The National Park Service puts a 10 dB rise at a doubling of perceived loudness and a ten-fold rise in sound level, so 68 dB(A) is about three times as loud as 52 dB(A) and carries roughly forty times the energy. The same scale gives conversational speech at 5 meters as 60 dBA.
Carried to a neighbor 30 meters off, the quiet machine reads 39 dB(A) and vanishes into a suburban night. The loud one reads 55 dB(A) — exactly the daytime residential ceiling in Portland City Code 18.10.010, and 5 dB over what that code allows after 10 pm.
That one choice at purchase decides whether the machine is a legal problem for years.
Carried to a neighbor 30 meters off, the quiet machine reads 39 dB(A) and vanishes into a suburban night. The loud one reads 55 dB(A) — exactly the daytime immission value TA Lärm section 6.1 sets for a general residential area, and 15 dB over the 40 dB(A) it allows there at night.
That one choice at purchase decides whether the machine is a legal problem for years.
What each fix is worth
Distance is the only entry here that costs nothing and never wears out.
| Move | Worth | Where the number comes from |
|---|---|---|
| Double the distance, from anywhere to anywhere | 6.0 | Inverse-square law |
| Move it from 7 m to 15 m away | 6.6 | Inverse-square law |
| Move it from 7 m to 30 m away | 12.6 | Inverse-square law |
| Solid wall that just breaks the line of sight | 5.0 | Federal Highway Administration |
| The same wall, one meter higher | 6.5 | Federal Highway Administration, 1.5 dB per meter |
| The same wall, two meters higher | 8.0 | Federal Highway Administration |
| A well-built barrier, practical ceiling | 10.0 | Federal Highway Administration, 5 to 10 dB band |
| Buying the canopied version of the same engine | ~19 | Class table above: open industrial 85 against canopied 66 |
A barrier counts only if it is solid and gap-free: sound leaks through a gap far better than it bends over a top edge, so a slatted fence is a visual screen and nothing acoustically.
Do not box a generator in without engineered ventilation. These machines need a large volume of cooling and combustion air, and starving one is a fire and carbon monoxide problem long before it is a noise fix.
Why the exhaust extension disappoints
A generator radiates from three paths at once: exhaust, engine casing, and the cooling fan with its air outlet. Decibels add logarithmically, so silencing one path can never take the total below what the other two already radiate.
Say the exhaust reads 70 dB(A) at the fence and casing plus fan read 66. The total is 71.5 dB(A). Remove the exhaust entirely and 66 is left: 5.5 dB for a perfect fix, and a real extension delivers part of that.
| Loudest path is above the next by | Maximum total reduction |
|---|---|
| 0 dB | 3.0 dB |
| 3 dB | 4.8 dB |
| 5 dB | 6.2 dB |
| 10 dB | 10.4 dB |
| 15 dB | 15.1 dB |
| 20 dB | 20.0 dB |
The order that works: quieter class, more distance, solid line-of-sight break, exhaust last. Size the machine first with the backup power calculator — an oversized set idling at a quarter load is louder and thirstier than a right-sized one working properly.
Quiet hours and the numbers that bind
No federal ceiling applies to a portable generator in the United States. The Environmental Protection Agency’s 1974 levels document, Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety, identified 55 decibels outdoors and 45 indoors as protective, stated as energy averages over 24 hours. It is guidance and was never made binding.
Inside a national park the limit is real. Under 36 CFR 2.12 it is prohibited to operate motorized equipment such as an electric generating plant that exceeds 60 decibels on the A-weighted scale at 50 feet in a developed area. Quieter noise is still prohibited where it is unreasonable for the time, the place, and the purpose the area was established for.
Parks then set their own hours on top of that. Great Smoky Mountains posts campground quiet hours of 10:00 pm to 6:00 am and generator quiet hours of 8:00 pm to 8:00 am.
At home the binding number is municipal. Portland City Code 18.10.010 allows 55 dBA in residential zones during day hours, 7 am to 10 pm, and 50 dBA during night hours, 10 pm to 7 am.
Read across from your own machine. Measured where the rule measures, at 50 feet, a 72 dB(A) open-frame set reads about 65 dB(A) and fails. To pass the 60 dBA test a machine has to publish about 67 dB(A) or less at 7 m, which admits the inverter and enclosed standby classes and rules out open-frame sets.
In Europe the machine is capped before it reaches you. Directive 2000/14/EC requires a guaranteed sound power level to be marked on outdoor equipment, and its Article 12 table limits welding and power generators below 400 kW.
At stage II, in force since 3 January 2006, the permissible level is 95 plus the logarithm of the electrical power up to 2 kW, 96 plus that logarithm from 2 to 10 kW, and 95 plus it above 10 kW, in dB relative to one picowatt.
That ceiling lands in a narrow band. A 5 kW set may not exceed 96.7 dB of sound power, a 20 kW set 96.3. Sound power becomes pressure at 7 meters by subtracting ten times the logarithm of two pi r squared, which is 24.9 dB, so both land near 72 dB(A) — why European open-frame sets cluster there.
What reaches the neighbor is governed nationally. In Germany the instrument is TA Lärm, the technical instruction on noise of 26 August 1998, which covers installations under the Federal Immission Control Act and leaves sports grounds to a separate ordinance.
Its section 6.1 values outside buildings run 50 dB(A) day and 35 at night in pure residential areas, 55 and 40 in general residential areas, 60 and 45 in core, village and mixed areas, and 65 and 50 in commercial areas.
Read across from your own machine. A 72 dB(A) open-frame set needs 279 meters to fall to the 40 dB(A) night value for a general residential area. A 52 dB(A) inverter needs 28 meters. That gap is the entire argument for the quieter class.
Where this chart stops
It is a planning chart. Walls reflect, ground absorbs and wind carries sound downwind, each worth a few decibels either way.
A-weighted decibels also under-count low frequency, and a single-cylinder engine turning the 3,000 or 3,600 rpm that makes grid frequency puts a lot of energy down there. Two machines that measure the same can annoy very differently, and the rumble is what travels through a wall.
Sources
36 CFR 2.12, audio disturbances. National Park Service: Great Smoky Mountains frontcountry camping, and Understanding Sound. Environmental Protection Agency, Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety, 1974. Federal Highway Administration, Keeping the Noise Down. National Institute for Occupational Safety and Health recommended exposure limit, 85 dBA averaged over an eight-hour workday. Directive 2000/14/EC, Article 12, stage II in force since 3 January 2006. TA Lärm of 26 August 1998, section 6.1. Portland City Code 18.10.010. Class bands are the published spread across manufacturer spec sheets and never a single model; the sound power to pressure conversion is the standard hemispherical relation. All read September 2026.
Go deeper
The backup power calculator turns a load list into kilowatts, and the generator fuel consumption chart shows why a right-sized set at half load beats an oversized one idling. Then whether you need a backup generator at all and standby generator against home battery, where the noise column decides it outright.