Decibel Chart

How the decibel scale works

A decibel (dB) is a unit for sound level. The scale is logarithmic, so equal steps do not add equal amounts of sound. These are the changes that matter most:

• +3 dB: double the sound energy.
• +10 dB: about twice as loud to the ear, and ten times the sound energy.
• Two equal sources together: about 3 dB louder than one source alone. Two identical sounds do not double the level.
• Distance from a small source in the open: doubling the distance lowers the level by about 6 dB.

Indoors, distance matters less, because walls, floors, and ceilings reflect sound back into the room. That is why the same source can read higher in a small, hard-walled room than in a large, soft one.

dBA and dBC on a chart

Charts usually list dBA, which is A-weighted. A-weighting follows how people hear everyday sound, so it counts less of the very low and very high pitches. C-weighting is nearly flat and counts bass. Charts list dBA because it is the standard for everyday noise and for hearing-safety limits.

When a chart gives a plain dB value, the weighting is not stated, and the number is a typical level. The hearing limits in this page are always in dBA. If a sound reads much higher in dBC than in dBA, it has a lot of bass, such as an engine or bass-heavy music.

Common sounds by setting

The levels below are typical values, not measurements of any one place. Each links to its Level Page, which has examples, a loudness comparison, a listening demo, and safe exposure time.

Notice the gap between 85 dB and 100 dB. Each +3 dB halves the safe time, so 85 dBA is safe for 8 hours a day and 100 dBA for only 15 minutes.

What levels mean for hearing

Four public bodies publish hearing guidance. They use different numbers and different purposes, so read each one for what it covers.

• NIOSH (US): recommends an exposure limit of 85 dBA averaged over 8 hours, with each +3 dB halving the safe time. It is the strictest guideline here.
• OSHA (US workplace law): permits 90 dBA for 8 hours, using a 5 dB exchange rate. Its action level of 85 dBA starts a hearing conservation program.
• CDC: sounds at or below 70 dBA are unlikely to cause hearing loss, even over long periods. Long or repeated exposure at 85 dBA or above can.
• WHO: safe listening guidance for adults is about 80 dB for up to 40 hours a week.

For sleep, the WHO guideline is different. It advises bedroom levels under 30 dBA, averaged over the night, and single noise events under 45 dBA.

Watch for two warning signs. If you have to shout to be heard at arm's length, the sound is too loud for the time you are spending in it. If you have ringing in your ears (tinnitus) or muffled hearing afterward, your ears were overloaded. Step away from the source and protect your ears.

Hearing protection helps when you cannot move away. Foam earplugs and earmuffs are rated by NRR in the US. Real-world protection is usually lower than the label, and well-fitted earplugs often cut 15 to 30 dB. A good fit matters more than the rating on the box.

Why chart numbers are typical

A chart number is a typical level, not an exact one. The same source can read differently depending on distance, the room it is in, and where the microphone or your ear sits. Move closer to a speaker and the level rises. Step into a large open space and it drops.

To check a sound yourself, open the meter on the home page. Measure for 30 to 60 seconds, hold the phone at ear height away from walls, and read Avg (Leq), the average over that time. Then compare that number with the chart to see roughly where the sound sits. A phone is an estimate, not a calibrated sound level meter, so use it to compare places and times more than to match a chart exactly.