Daily Noise Exposure Calculator

Why the two results differ: 3 dB against 5 dB

The EU and GB formula adds sound energy. Ten times the energy is 10 dB, and doubling it is about 3 dB, so every 3 dB increase halves the time it takes to reach the same daily exposure. OSHA's Table G-16a halves the reference duration for every 5 dB instead, starting from 8 hours at 90 dBA. OSHA also leaves levels below 80 dBA out of the hearing conservation dose and levels below 90 dBA out of the PEL dose, while the EU and GB method counts all noise at work. The table shows the time at a steady level after which each trigger is reached, with nothing else added to the day.

At 85 dB(A) both regimes allow eight hours before the 85 trigger. At 100 dB(A) the EU and GB upper action value is reached after about 15 minutes and the OSHA action level after one hour. A steady level below 90 dBA never adds to the PEL dose, because the PEL is measured with a 90 dBA threshold. The values are rounded to the nearest minute.

What the calculation does

EU and GB. For each task the time in hours is divided by 8 and multiplied by 10 raised to the level divided by 10. The results are added, and LEX,8h is 10 times the base-10 logarithm of the sum. This is the multi-period formula in Schedule 1 of the Control of Noise at Work Regulations 2005, with T0 of 8 hours, which the Schedule says corresponds to LEX,8h in ISO 1999:1990; Directive 2003/10/EC defines LEX,8h by the same reference. A day longer than 8 hours is still spread over 8 hours, so it raises the result.

OSHA. For each task the reference duration is T = 8 ÷ 2^((L − 90) ÷ 5) hours, the formula behind Table G-16a in Appendix A of 29 CFR 1910.95. The dose is 100 × the sum of the task times divided by their reference durations, and the TWA is 16.61 × log10(dose ÷ 100) + 90. The hearing conservation dose counts tasks from 80 to 130 dBA, as 1910.95(d)(2)(i) requires; the PEL dose counts tasks from 90 dBA, the threshold OSHA's Technical Manual gives for the PEL.

Rounding. LEX,8h, the TWA and the peak are shown to one decimal, as in OSHA's conversion table, and every comparison uses the value as shown, so the text and the figure always agree. Doses are shown to one decimal of a percent so that a sum such as 7/8 reads as 87.5%; OSHA's own examples print whole percentages. A level reaches an action value when it is equal to or above it and exceeds a limit only when it is above it. The OSHA PEL is judged on the dose, because the footnote to Table G-16 says a mixed exposure exceeds the limit when the sum of C/T exceeds 1: a dose of 100.1% to 100.6% is shown as exceeded although its TWA still reads 90.0 dBA, and a dose of exactly 100.0% is shown as “At 100%”. Nothing is stored or sent.

Worked examples from the sources

• Machine shop (OSHA Technical Manual, Appendix B.4). A worker spends 2 hours at 95 dBA on a milling machine, 15 minutes in the break room at 69 dBA, 3 hours in the parts department at 78 dBA, a 45-minute lunch in the break room at 69 dBA and 3 hours at 90 dBA as milling assist. OSHA leaves out the periods below 90 dBA, adds 2/4 + 3/8 = 7/8 and finds the result below 1, so the PEL is not exceeded. The calculator, which opens with these five periods, gives a PEL dose of 87.5% and a TWA of 89.0 dBA; the same figures apply to the action level, because the other periods are below 80 dBA, so the action level is reached. The same day gives an EU and GB LEX,8h of 90.8 dB(A): above the upper action value, and above 87 dB(A) unless hearing protection brings the exposure at the ear down.
• Extended shift (OSHA Technical Manual, Section IV.E). A 9.5-hour shift averaging 86.3 dBA gives a 71% dose and a TWA of about 87.5 dBA, so a hearing conservation programme is required. Entered as one task of 9 hours 30 minutes at 86.3 dB(A), the calculator gives 71.1% and 87.5 dBA. The EU and GB figure is 87.0 dB(A) (87.05 unrounded): at the limit value, not above it, which is the kind of result where measurement uncertainty decides the answer.
• Dose to TWA (29 CFR 1910.95 Appendix A; Technical Manual, Appendix B.8). A dose of 91% is a TWA of 89.3 dBA and a dose of 50% is 85 dBA; a dose of 183% is 94.4 dBA. The calculator's conversion returns the same values.
• Our own illustration. The noise and hand-arm vibration guide uses 4 hours at 88 dB(A) and 4 hours at 78 dB(A), which gives an LEX,8h of 85.4 dB(A), above the upper action value. Under OSHA the 78 dB(A) half is not counted and the dose is 37.9%, a TWA of 83.0 dBA, below the action level.

The tests for this page reproduce these figures with the calculator's own functions. HSE publishes worked examples in its L108 guidance and ready-reckoners; see below for why they are not reproduced here.

Why the result can mislead

The result is only as good as the level entered for each task. A short spot reading at a machine is not the level a person receives while moving around, and a level that varies within a task is not one number: the EU and GB method needs the equivalent continuous level, LAeq, while OSHA measures on the A scale at slow response and integrates with a 5 dB exchange rate, so the same fluctuating noise can give different task levels under the two regimes. Personal dosimetry over representative shifts reduces this problem.

Directive 2003/10/EC Article 4(5) requires measurement inaccuracies to be taken into account, so a result within a decibel or two of a value cannot be read as clearly above or below it. Impulsive noise needs the peak as well as the daily figure. Where exposure varies markedly from day to day, the directive and the GB Regulations allow a weekly exposure instead, which this calculator does not compute. The OSHA part covers general industry. Construction work falls under 29 CFR 1926.52, which has the same table of permissible exposures but no 85 dBA action level: it requires a hearing conservation programme wherever the levels in its table are exceeded. OSHA's Technical Manual also describes an allowance for instrument error in enforcement, which is not applied here. Hearing protection is left out on purpose: whether it brings the exposure at the ear below 87 dB(A), or protects enough under OSHA's Appendix B methods, needs its own assessment.

On shifts longer than 8 hours, the OSHA Technical Manual (Section III, Chapter 5, IV.E) applies the permissible exposure limit to any period or periods of exposure summing 8 hours within the shift, which must stay below a 90 dBA TWA. This calculator adds up the whole shift, which gives the highest dose, so a PEL result here does not show which 8 hours an inspector would assess.

Where the formulas and values come from

• Directive 2003/10/EC: Article 2(b) defines LEX,8h by reference to ISO 1999:1990 point 3.6; Article 3 sets 80, 85 and 87 dB(A) and 135, 137 and 140 dB(C), with the limit values taking account of hearing protectors and the action values not; Articles 4 to 7 and 10 set the duties. We read the original text from the EU Publications Office and the copy of the EU text on legislation.gov.uk.
• The Control of Noise at Work Regulations 2005: regulation 2 defines daily personal noise exposure, regulation 4 sets the same values for Great Britain and regulation 4(5) the hearing protector rule, and Schedule 1 gives the LEP,d formulas used here.
• HSE's noise pages on the Regulations and on action and limit values, its exposure calculators and ready-reckoners, and the landing page of L108, Controlling noise at work (third edition, 2021).
• 29 CFR 1910.95 on eCFR: Table G-16 and its footnote, paragraphs (c), (d), (g), (i) and (k), Appendix A with Table G-16a and Table A-1. eCFR lists 1 June 2022 as the section's latest amendment date. OSHA publishes the same text on osha.gov.
• OSHA Technical Manual, Section III, Chapter 5 (Noise): the 90 dBA PEL threshold and 80 dBA action level threshold, the extended-shift example in Section IV.E, the 2 dB instrument-error allowance and Appendices B.4, B.8 and B.9.

All of these were opened on 22 October 2026. They describe the law and methods; they do not validate this calculator or any particular result.

What we could not verify (22 October 2026)

• HSE's worked examples sit in L108 and the daily and weekly ready-reckoners, which HSE offers as PDF files, and its noise exposure calculator is a spreadsheet. We did not open them, so this page does not reproduce HSE's own examples or confirm how HSE rounds its results. The GB figures here come from the formula in Schedule 1 of the Regulations.
• We read the directive's original text (CELEX 32003L0010) through the EU Publications Office and the copy on legislation.gov.uk; Articles 2, 3, 4(5), 5, 6, 7 and 10 match. EUR-Lex lists a consolidated version of 26 July 2019 and amendments by Directive 2007/30/EC and Regulations (EC) No 1137/2008 and (EU) 2019/1243 that touch Articles 12, 12a, 12b, 13 and 16 only; we did not read the consolidated text itself. Member States may set stricter national rules.
• ISO 1999:1990 and ISO 9612, the measurement standard, are sold by ISO and were not opened. We rely on the GB Schedule's statement that its formula corresponds to LEX,8h in ISO 1999:1990.
• We read 29 CFR 1910.95 on eCFR rather than on osha.gov. The Technical Manual chapter was read in a browser; we recomputed each of its figures used here and they agree with the formulas. Where the Manual and the regulation word the PEL test differently (a sum of C/T equal to 1), this page follows the regulation and flags the case.

Recording the assessment

The noise and hand-arm vibration compliance guide covers measurement strategy, controls, hearing protection and health surveillance. To record the levels, durations, assessor and actions for a group of workers, use the free workplace exposure assessment record template.