Generator hours and decibel limits in national park campgrounds

In a US national park, a generator must not be louder than 60 decibels on the A-weighted scale, measured 50 feet (15.2 m) away. That limit is federal law, 36 CFR 2.12. The hours are not federal. Each park sets them in its own rules. Yosemite allows 7 to 9 am, 12 to 2 pm and 5 to 7 pm. Yellowstone bans generators from 8 pm to 8 am.

What does "60 dB(A) at 50 feet" mean?#

A decibel (dB) is a unit of loudness on a log scale. Each step of 10 dB is ten times the sound intensity. HyperPhysics notes that it takes about 10 dB more to sound twice as loud.

The A in dB(A) means A-weighted. A sound meter set to A weighting "filters out significantly more bass", in HyperPhysics' words, so it hears more like a human ear does.

At 50 feet is where the reading counts. Sound fades with distance, so a decibel figure means nothing until you know how far away it was taken. Fifty feet is 15.24 m.

Here is the rule itself. 36 CFR 2.12(a)(1) prohibits running "motorized equipment or machinery such as an electric generating plant" in a manner:

(i) That exceeds a noise level of 60 decibels measured on the A-weighted scale at 50 feet; or, if below that level, nevertheless; (ii) makes noise which is unreasonable, considering the nature and purpose of the actor's conduct, location, time of day or night, purpose for which the area was established, impact on park users, and other factors...

So there are two tests, not one. Part (i) is a number. Part (ii) can catch a generator that passes the number, for example at 10 pm.

A second part of the same rule matters for anyone camping away from a campground. Paragraph (a)(3) bans "any type of portable motor or engine" in nondeveloped areas unless you hold a permit. In practice the generator question is a campground question.

The rule sets no hours at all. Those live in each park's superintendent's compendium. A compendium is the park's own written list of local rules, signed by the park superintendent. Two parks can apply the same federal noise limit and still allow very different hours.

Generator hours by park#

The table below sets six parks side by side. Each row is read from that park's own compendium, except Grand Canyon. Its compendium page showed "Page In-Progress" in November 2026, so its row comes from the Mather Campground bulletin the park hosts.

Most parks give you short morning, midday or evening windows, four to six hours a day in total. Yellowstone and the Smokies set a curfew instead: daytime use is allowed, as long as it meets the noise rule. The banned lists are specific down to the loop. In the Smokies, Cades Cove C loop allows generators only while B loop is closed, so check the loop, not just the campground.

Zion and the Smokies also allow for medical need. The Smokies grant waivers for "the powering of medical equipment" during quiet hours. Zion decides medical cases in Watchman's A and B loops "on a case by case basis". If you sleep with a CPAP, ask the park before you arrive, and size a battery as well. How long a CPAP runs on a battery has the figures.

National forests and state parks use different rules#

The Forest Service rule has no number. 36 CFR 261.10(i) bans running a "motor or engine" in or near a campsite "in such a manner and at such a time so as to unreasonably disturb any person". So a generator that would pass the park test can still break this rule, and the federal text gives no hours to plan around. Read the rules posted at the campground.

California's state park rule is more specific. Under 14 CCR 4320, no one may run "an engine driven electric generator" that is likely to disturb others "between the hours of 8 p.m. and 10 a.m." without the Department's permission. That leaves 10 am to 8 pm, ten hours a day.

Why two answers circulate#

Ask about this online and you will hear two answers. One says you need a generator rated under 60 dB. The other says any inverter generator is fine. Both come from the same mistake: comparing the number on the box with the number in the rule as if they were taken at the same distance.

They are not. The rule measures at 50 feet. Yamaha's EF2200iS sheet gives both of its figures "at 7 m", less than half that distance, so its box number is louder than its 50 foot number. A generator rated 62 dB(A) at 7 m does not break a 60 dB rule at 50 feet. It works out to about 55.

The "any inverter is fine" answer misses three things: the quiet quarter-load figure can be the headline, two generators together are louder than one, and the hours are a separate rule.

Even one maker can print two figures for one model. Honda's US product page lists the EU2200i at 57 dB(A) at rated load and 48 at quarter load, with no distance on the page. Honda's 2017 specification release for the same model gave 62 dB and 53 dB, also with no distance. A figure without a distance cannot be converted, so it cannot be checked against the rule.

The decibel limit is easy to check with arithmetic. The hours are what most campers actually run into.

Worked example: turning a 7 metre rating into 50 feet#

Take the Yamaha EF2200iS, the 230 volt model on Yamaha's global site. Yamaha lists 65 dB(A) at rated load and 57 dB(A) at quarter load, both at 7 m. Here is how that converts to the park's distance.

1. Convert 50 feet to metres. 50 x 0.3048 = 15.24 m.
2. Find the distance ratio. 15.24 / 7 = 2.18.
3. Find the drop in decibels. Sound from a small source spreads over a growing sphere, so its intensity falls with the square of the distance. That is the inverse square law. In decibels the drop is 20 x log10(2.18) = 6.76 dB, or about 6.8.
4. Subtract. At rated load, 65 minus 6.8 is 58.2 dB(A) at 50 feet. At quarter load, 57 minus 6.8 is 50.2 dB(A).

So this generator, at full load, comes in just under the park limit. At quarter load it has almost 10 dB to spare.

Now suppose you run two of them linked together for more power. Two equal sources double the sound intensity. In decibels that adds 10 x log10(2) = 3.0 dB. At rated load that gives 58.2 + 3.0 = 61.2 dB(A) at 50 feet: over the limit. At quarter load the pair gives 53.2 dB(A), still under it.

The same arithmetic works for any rating taken at 7 m. Every doubling of distance takes off another 6.0 dB (20 x log10(2) = 6.02).

The threshold to remember is about 66.8 dB(A) at 7 m. A single generator rated above that, at the load you will run, is likely to fail the park test. One rated well below it is likely to pass the number, and then only the hours and the "unreasonable" test remain.

If a sheet gives its figure at 1 m, the drop to 50 feet is 20 x log10(15.24) = 23.7 dB. If it gives no distance, you cannot convert it.

The overnight gap is what your battery has to cover#

Every park in the hours table leaves a long stretch with no generator. The shortest is Grand Canyon's 11 hours. The longest is Glacier's 13. A generator-free loop leaves all 24.

That gap decides how much battery you need. A portable power station, a battery with its own inverter and sockets, has no engine and makes no exhaust. It is the quiet way to keep a fridge, a fan or a CPAP running through the night.

Here is the arithmetic for one load. Our 12 volt power and fridges guide uses 300 Wh a day as the working figure for a 35 to 50 litre compressor fridge. Spread over 24 hours, that is 12.5 Wh an hour. Divide by 0.85 to cover conversion losses, as the power bank sizing guide does throughout.

The last row is the one to plan around. In a generator-free loop, the battery must carry the whole trip, or a panel must refill it. Three days at 353 Wh is 1,059 Wh of battery. Solar for camping shows when a panel can make up the difference, and it makes no noise at all.

The windows also limit how fast you can refill. Putting 191 Wh back during a single 2 hour window needs at least 96 W of charging, before any charging losses. A station that accepts only 60 W would need more than three hours, longer than any of the 2 hour windows.

To size your own setup, add up your loads in the power budget calculator. Then check the result against the longest gap in your park.

Check your generator before the trip#

You can do all of this at home in a few minutes.

1. Find the noise line on the spec sheet. Note three things: the dB(A) figure, the distance and the load.
2. Use the rated-load figure. The quarter-load number is the quiet one. If you will run an air conditioner or a kettle, you will be near rated load.
3. Convert to 50 feet. For a figure at 7 m, subtract 6.8. For a figure at 1 m, subtract 23.7. With no distance stated, treat the figure as unknown.
4. Add 3 dB for a pair. Two identical generators linked together are 3 dB louder than one.
5. Read the current compendium for your park. Find the generator hours and the list of generator-free loops. Then check which loop your site is in.
6. Set a phone alarm for five minutes before each window ends.
7. Size the battery for the gap. Use the longest gap in your park, or 24 hours if your loop is generator-free.

Common mistakes#

Quoting the quarter-load figure. It can be the headline number, and it is not the one you will be running at when the air conditioner kicks in.

Running a few minutes past the window. The windows are written to the minute. In Yosemite, 7:00 pm is the end, not a target.

Choosing a generator-free loop and running it anyway. Zion's Watchman, Glacier's Sprague Creek and several Smokies loops ban generators at all times, however quiet.

Idling the vehicle instead. The Smokies forbid "the idling of engines to recharge batteries" in generator-free areas. Zion requires engines off while parked unless people are loading or unloading.

Leaving it running at an empty site. The Smokies say generators "may not be left running when the campsite is unattended". Zion says a generator "may not be left running on any vehicle", except an RV in its campsite during the approved hours.

What this answer does not cover#

The conversion is an estimate. HyperPhysics notes that sound follows the inverse square law only "if there are no reflections or reverberation". An RV wall behind the generator, a canyon wall or a row of parked vehicles can make the real reading at 50 feet louder than the arithmetic says. The figure that counts is a ranger's meter at your site, not a spec sheet.

Passing 60 dB(A) is not a safe harbour. Part (ii) of the rule makes "unreasonable" noise an offence even below the number. A legal generator at a legal hour can still draw a complaint if it runs the whole window next to a tent.

The hours change. Yosemite's compendium was approved in May 2026 and Yellowstone's in September 2026. Grand Canyon's row comes from a campground bulletin, not a compendium, and the bulletin file on nps.gov is dated 2017. This page covers six parks, and every other park writes its own rules. Read the current compendium and the campground's own posted rules in the week you go.

Battery power stations are not named in any of the park rules quoted here. They name generators and engines. If you are unsure whether a device counts, ask the campground before you rely on it.

Finally, this page is about noise and hours only. A generator burns fuel and makes exhaust. Where to put it relative to a tent is the same question covered for heaters in using a diesel heater in a tent.

Frequently asked questions#

What is the decibel limit for generators in national parks?#

60 decibels on the A-weighted scale, measured 50 feet (15.2 m) from the generator. The limit comes from 36 CFR 2.12(a)(1) and applies in every national park. The same rule also bans noise that is "unreasonable" for the time and place, even when it is below 60 dB(A). Generator hours are set separately, by each park's superintendent's compendium.

What are the generator hours in Yosemite?#

Yosemite's compendium, approved 27 May 2026, allows generators only from 7 to 9 am, 12 to 2 pm and 5 to 7 pm. That is six hours a day, with a 12 hour gap from 7 pm to 7 am. The 60 dB(A) at 50 feet noise limit applies during those windows.

Can you run a generator overnight in a national park?#

Generally not in the six parks on this page. Yellowstone and Great Smoky Mountains ban generators from 8 pm to 8 am, and the others allow only short daytime windows. Yellowstone makes exceptions only in areas marked by signs or approved by an official. The Smokies can grant a waiver for medical equipment, and Zion decides medical cases in Watchman's A and B loops one by one. Otherwise, a battery has to carry the night.

Is a 60 dB generator quiet enough for a national park?#

Usually, yes, if the 60 dB is measured at 7 m (23 ft), the distance Yamaha's spec sheet uses. At 50 feet that becomes about 53 dB(A), under the limit. Check that the figure is for rated load, not quarter load. Two such generators linked together add 3 dB. The park's hours still apply.

Can you use a generator in a national forest campground?#

The Forest Service rule, 36 CFR 261.10(i), sets no decibel figure and no hours. It bans running a motor or engine in or near a campsite in a way that would "unreasonably disturb any person". So the hours you can run it are those posted at the campground. Read the rules board when you arrive.

Are generators allowed in California state parks?#

Yes, with limits. Under 14 CCR 4320, a generator that is likely to disturb others may not run between 8 pm and 10 am without the Department's permission. Quiet hours in campgrounds run from 10 pm to 6 am. That leaves a 10 am to 8 pm window, ten hours a day.