How to check a noise level against a limit
There is no federal community noise standard in the United States. EPA's 1974 Levels Document recommends an outdoor Ldn of 55 dBA to protect public health and welfare, but it is guidance with no enforcement power. Enforceable limits for neighborhood, construction, and commercial noise are written by cities and counties in their own noise ordinances, and the numbers vary widely between jurisdictions. That is why this calculator prefills a reference value and then lets you type the limit that actually applies to your site.
Background noise is removed logarithmically rather than by simple subtraction. The corrected source level is 10 log10(10^(Lm/10) - 10^(Lb/10)). When the measured and background levels are within 3 dB of each other the source contributes too little to separate reliably, so the calculator rejects the reading and asks for a re-measurement. A measurement of 58 dBA against a 50 dBA background corrects to about 57.3 dBA.
Workplace exposure is a separate matter governed by OSHA 1910.95. The permissible exposure limit is 90 dBA as an 8-hour time-weighted average with a 5 dB exchange rate, so allowable time is T = 8 / 2^((L-90)/5). A dose above 100 percent exceeds the PEL, and a dose of 50 percent, equivalent to the 85 dBA action level, triggers a hearing conservation program. Check your local ordinance text and consult an acoustical consultant or industrial hygienist before relying on these results in an enforcement matter. Values reflect rules in effect as of September 2026.
Frequently asked questions
No. EPA published a 55 dBA Ldn outdoor level in its 1974 Levels Document as guidance only, and Congress never gave it enforcement authority. Enforceable community noise limits come from city and county noise ordinances, so you must look up the one for your jurisdiction.
OSHA 1910.95 uses a 5 dB exchange rate rather than the 3 dB rate used by NIOSH and many other countries. Starting from 90 dBA for 8 hours, every additional 5 dBA cuts the permissible time in half, so 95 dBA allows 4 hours and 100 dBA allows 2.