Noise Dose Calculator | Daily Noise Exposure and 8-Hour TWA
Free tool to calculate a worker's noise dose and 8-hour noise exposure from sound level readings, and check it against the Indian Factories Rules, NIOSH, Abu Dhabi OSHAD-SF and EU limits in one go.
Noise Dose Calculator
How to use this calculator
- Add one row for each task or area the worker spends time in during the day.
- Enter the A-weighted sound level, dB(A), measured at the worker's ear position, and the time spent there in minutes.
- Click Calculate. You get the result under each standard side by side, so you can see which limits are met and which are not.
- Save the result with Download, Print / Save PDF or Copy Summary.
Result
Screening tool for awareness and planning. Results depend on the quality of your measurements. A competent person should carry out the formal noise assessment used for compliance decisions.
Noise Limits at a Glance
| Standard | 8-hour limit | Exchange rate | Time allowed at 100 dB(A) | Levels counted |
|---|---|---|---|---|
| India – Factories Rules | 90 dB(A) | 5 dB (time halves every +5 dB) | 2 hours | 90 dB(A) and above |
| NIOSH REL / Abu Dhabi OSHAD-SF | 85 dB(A) | 3 dB (time halves every +3 dB) | 15 minutes | 80 dB(A) and above (NIOSH) |
| EU / UK / ISO 9612 | Action values 80 and 85 dB(A); limit 87 dB(A) with hearing protection | 3 dB (energy average) | – (uses LEX,8h) | All levels |
| OSHA (USA) | 90 dB(A) PEL; 85 dB(A) action level | 5 dB | 2 hours | 80–130 dB for the action level |
How to Interpret Your Result
| Result | Band | What it means / action |
|---|---|---|
| Dose below 50% (EU: LEX,8h below 80 dB(A)) | Acceptable | Exposure is below the action level. Keep noise in mind when buying machines or changing the layout, and re-check when the process changes. |
| Dose 50% to 100% (EU: 80 to 85 dB(A)) | Action needed | Near the limit. Provide hearing protection and training, mark noisy areas, plan noise reduction, and start audiometry where your rules require it. |
| Dose 100% or more (EU: 85 dB(A) or more), or a level above the absolute maximum | Exceeds limit | Over the limit. Reduce noise at the source or cut exposure time, make hearing protection mandatory, sign-post the area, and run a hearing conservation programme with annual audiometry. |
A dose of 50% equals an 8-hour level of 85 dB(A) under the 5 dB rule and 82 dB(A) under the 3 dB rule. The calculator shows each standard's own band, because the same exposure can pass one standard and fail another.
When Do You Need to Calculate Noise Dose?
- Workers move between noisy and quiet areas. A single sound level reading does not show daily exposure. Dose adds up every task.
- Factory inspection, client audit or ISO 45001 audit. You need numbers to show workers are within limits and that hearing protection zones are correctly set.
- New machines or layout changes. Compressors, DG sets, grinders, presses, crushers, blowers and pumps change exposure for everyone nearby.
- Setting up audiometry. Exposure results decide who must be in the hearing conservation programme.
- Working for multinational or Middle East clients. They often apply the 85 dB(A), 3 dB rule, which is far stricter than the Indian 90 dB(A), 5 dB rule.
Data to Collect Before You Calculate
| Input | Where to get it | Practical tip |
|---|---|---|
| Sound level, dB(A) | Sound level meter (IEC 61672, Class 1 or 2) or personal noise dosimeter | Use A-weighting. Indian rules specify slow meter response. Measure at the worker's ear position, not near the wall or at the machine. |
| Equivalent level for varying noise (LAeq) | Integrating meter or dosimeter running for the whole task | Do not average decibel readings by hand. Let the meter integrate, or use this calculator's energy average. |
| Time at each level | Observation, job rotation chart, interviews with the worker and supervisor | Include short, loud tasks such as grinding, blowing down and hammering. Under the 3 dB rule they often decide the result. |
| Impulse noise | Meter with peak, dB(C) peak, measurement | Hammering, riveting and press impacts need a separate peak check. This calculator covers continuous noise only. |
Noise Dose Formulas Explained
1. Noise dose (all standards)
- C = time actually spent at a level (hours)
- T = time allowed at that level (hours), from the formula of the standard you follow
2. Time allowed at each level
L is the sound level in dB(A). For example, at 95 dB(A) the time allowed is 4 hours under the 5 dB rule and about 48 minutes under the 3 dB rule. The Indian table (90 dB(A) for 8 h, 95 for 4 h, 100 for 2 h, 105 for 1 h, 110 for 30 min, 115 for 15 min) follows the 5 dB formula; the calculator uses the formula, which matches the table within rounding.
3. Converting dose to an 8-hour level
4. Daily noise exposure LEX,8h (EU / ISO 9612)
This is the energy average of all exposures, normalised to an 8-hour day. It is the figure compared with the EU action values of 80 and 85 dB(A) and the 87 dB(A) limit.
Worked Example: Fabrication Shop Grinder Operator
A fitter in a fabrication shop works an 8-hour shift. Sound level readings at his ear position give three periods.
| Task | Level | Time (C) | India: T allowed | India: C/T | NIOSH / OSHAD: T allowed | NIOSH / OSHAD: C/T |
|---|---|---|---|---|---|---|
| Grinding | 100 dB(A) | 1 h | 2 h | 0.50 | 0.25 h | 4.00 |
| Fabrication work | 95 dB(A) | 3 h | 4 h | 0.75 | 0.79 h | 3.78 |
| General shop | 88 dB(A) | 4 h | not counted (below 90) | 0 | 4 h | 1.00 |
| Total | 1.25 = 125% | 8.78 = 878% | ||||
- As per Indian Factories Rules: dose 125%, equal to 91.6 dB(A) over 8 hours. Exceeds limit.
- As per NIOSH / Abu Dhabi OSHAD-SF: dose 878%, equal to 94.4 dB(A) over 8 hours. Exceeds limit by a wide margin.
- As per EU / ISO 9612: LEX,8h = 94.4 dB(A), above the 85 dB(A) upper action value.
Quick scenarios
| Situation | Inputs | India | NIOSH / OSHAD | EU LEX,8h |
|---|---|---|---|---|
| Control room operator | 75 dB(A) for 8 h | 0% (below 90) | 0% (below 80) | 75.0 dB(A) – acceptable |
| Short compressor house rounds | 98 dB(A) for 30 min, rest quiet | 18.9% – acceptable | 126% – exceeds | 86.1 dB(A) – upper action |
| Breaker / jackhammer work | 105 dB(A) for 2 h | 200% – exceeds | 2,539.8% – exceeds | 99.0 dB(A) – upper action |
The compressor house case is the one most sites miss: half an hour a day looks harmless under the Indian rule but is over the limit under the stricter rule many clients use.
Legal Limits and Standards for Noise Exposure
| Region / standard | Key requirements |
|---|---|
| India – Factories Act 1948 and state Factories Rules (now consolidated under the OSH Code 2020, in force from 21 November 2025) | Maharashtra Factories Rules, Schedule XXIV (Rule 114): 90 dB(A) for 8 h, down to 115 dB(A) for 15 min; combined exposure must not exceed 1 (sum of C/T); levels below 90 dB(A) may be ignored; no exposure above 115 dB(A); impulse noise above 140 dB peak not permitted (100 impulses a day at 140 dB). Gujarat Factories Rules, Schedule XXIII (Rule 102): high noise means 90 dB(A) or above; reduce exposure by engineering or administrative controls, provide ear protectors, and do audiometry within 14 days of joining and at least every 12 months. |
| UAE – Abu Dhabi OSHAD-SF CoP 3.0 Occupational Noise (v3.1, 2018) | 85 dB(A) 8-hour TWA with the 3 dB rule (T = 8 ÷ 2(L−85)/3); no exposure above 100 dB(A) without suitable hearing protection; hearing protector rating derated (NRR minus 7 dB); baseline audiogram within 6 months and then yearly. |
| NIOSH REL (USA, recommended) | 85 dB(A) 8-hour TWA, 3 dB exchange rate, levels from 80 to 140 dB(A) integrated, no exposure above 140 dB(A). |
| OSHA 29 CFR 1910.95 (USA) | 90 dB(A) PEL with 5 dB exchange (Table G-16); hearing conservation programme at 85 dB(A) TWA (50% dose), integrating 80 to 130 dB; impulse noise not to exceed 140 dB peak. |
| EU Directive 2003/10/EC (and UK regulations based on it) | LEX,8h action values 80 and 85 dB(A) (peak 112 and 140 Pa); exposure limit 87 dB(A) (peak 200 Pa), which takes hearing protection into account. Action values do not take hearing protection into account. |
Rules differ between states and change over time. Check your state's rules under the OSH Code, your client's specification and the current version of each standard before using any value for compliance.
Common Mistakes When Calculating Noise Exposure
- Averaging decibels like normal numbers. Decibels are logarithmic. Equal time at 90 and 100 dB(A) averages 97.4 dB(A), not 95.
- Mixing the 3 dB and 5 dB rules. Using the Indian table to check a client's 85 dB(A) requirement badly underestimates exposure. Pick the standard first, then calculate.
- Ignoring short, loud tasks. Thirty minutes at 98 dB(A) is fine under the Indian rule but over the limit under the 3 dB rule.
- Using area readings as personal exposure. Workers move. Measure at the ear position for each task, or use a personal dosimeter.
- Counting hearing protection too early. Calculate exposure without hearing protection first. Protection decides whether the protected exposure is acceptable, not whether action is needed.
- Taking the protector's label rating at face value. Real-world protection is lower. Derate the rating (for example, NRR minus 7 dB as Abu Dhabi OSHAD-SF requires).
How to Reduce Noise Exposure
- At the source: buy low-noise machines, maintain bearings and belts, fit silencers on exhausts and air blow-off, use low-noise grinding discs and nozzles.
- On the path: enclosures, acoustic screens and barriers, absorptive panels, separating noisy machines from work areas, and acoustic control rooms.
- By time: rotate workers through noisy tasks and schedule noisy work when fewer people are present.
- Hearing protection as the last line: choose plugs or muffs with enough derated attenuation, train people to fit them, and enforce use in marked zones.
- Hearing conservation programme: noise mapping, audiometry, records, and annual review.
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Important Disclaimer & Professional Support
This calculator gives a screening estimate for continuous noise. A formal noise assessment also needs a suitable measurement strategy, calibrated instruments, impulse noise checks and the limit that legally applies to your site.
Need a workplace noise survey or hearing conservation programme? Himaya Prevention provides noise mapping, personal noise dosimetry, hearing protection selection, occupational health centre support and HSE training across India and the Middle East.
Contact Himaya Prevention · sales@himpre.com · WhatsApp +91 79 9060 2143
Frequently Asked Questions
How do you calculate noise dose?
For each task, divide the time spent by the time allowed at that sound level, add the fractions and multiply by 100. For example, 1 hour at 100 dB(A) and 3 hours at 95 dB(A) under the Indian rule gives 100 × (1/2 + 3/4) = 125%.
What is the permissible noise level in India?
Under the state Factories Rules, workers may be exposed to 90 dB(A) for 8 hours, with the allowed time halving for every 5 dB increase, and no exposure above 115 dB(A). Check the rules notified for your state under the OSH Code 2020.
What is the difference between the 3 dB and 5 dB exchange rates?
The exchange rate is how much the level can rise before the allowed time halves. The 3 dB rule (NIOSH, Abu Dhabi OSHAD-SF, EU) follows the physics of sound energy and is stricter. The 5 dB rule (India, OSHA) allows much longer times at high levels.
How long can a worker be exposed to 100 dB(A)?
Two hours a day under the Indian Factories Rules and OSHA, but only 15 minutes a day under NIOSH and Abu Dhabi OSHAD-SF. Use the standard that applies to your site or client.
Does hearing protection change the noise dose?
Dose is calculated from the noise at the ear without protection. Hearing protection reduces what reaches the ear, so it decides whether the protected exposure is acceptable. Under EU rules, action values ignore protection while the 87 dB(A) limit includes it.
Why can't I average decibel readings?
Decibels are on a logarithmic scale, so every 3 dB increase doubles the sound energy. An arithmetic average underestimates exposure. Use the LEX,8h energy average or the dose method.
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References
- Maharashtra Factories Rules, 1963 – Schedule XXIV (Rule 114), Operations involving high noise levels.
- Gujarat Factories Rules, 1963 – Schedule XXIII (Rule 102), Operations involving high noise levels; Occupational Safety, Health and Working Conditions Code, 2020.
- Abu Dhabi OSHAD-SF Code of Practice CoP 3.0 – Occupational Noise (Version 3.1, June 2018).
- NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998.
- OSHA, 29 CFR 1910.95 Occupational noise exposure, including Appendix A (noise exposure computation).
- Directive 2003/10/EC on the exposure of workers to noise; ISO 9612 Determination of occupational noise exposure.
Prepared and reviewed by the HSE team at Himaya Prevention Private Limited, Vadodara, India. Last reviewed: October 2026. Health | Safety | Environment | Fire | Quality · designed & automated by hsefq.com
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