Combine sound energy, not decibel averages
For each task, use its measured A-weighted equivalent sound level and actual duration. The method sums energy across periods, then normalises to an eight-hour reference day.
Tᵢ = task duration in hours; Lᵢ = task LAeq in dB(A).
For a single period this reduces to L + 10 log₁₀(T / 8). A longer shift is still normalised to eight hours; do not change the reference to match shift length. The energy formula comes from Schedule 1 of the Control of Noise at Work Regulations 2005.
Exposure points = 100 × 10(LEP,d − 85)/10. This is the precise energy equivalent; HSE’s printed ready-reckoner uses rounded values. Points are not an OSHA noise-dose percentage.
Supported level range is 0–200 dB(A), a software input bound rather than an instrument specification. Durations must be positive, non-overlapping and total no more than 24 hours. Do not enter simultaneous sources as separate overlapping exposure periods; use the combined measured level.
Follow a simple example
Imagine one person works at a cutting station for 4 hours, then packs items for 4 hours. A noise assessment gives these fictional readings:
- Task 1 — cutting: 85 dB(A), 4 hours, 0 minutes.
- Task 2 — packing: 80 dB(A), 4 hours, 0 minutes.
Select “Try a filled example” to put these figures into the calculator. Your result will be 83.2 dB(A). This represents the combined daily exposure on an eight-hour reference basis, not the sound level at either station.
Task names and readings are illustrative. Cutting and packing do not always have these noise levels.
Check the numbers
85 dB(A) for 8 hours → 85.0 dB(A), 100 exposure points.
For 4 hours at 85 dB(A) and 4 hours at 80 dB(A), daily exposure is approximately 83.18 dB(A), or 65.81 points. These are illustrative readings, not an assessment of a real workplace.
Understand the scope
HSE describes lower and upper daily or weekly exposure action values of 80 and 85 dB(A). Compare action values with exposure before the effect of hearing protection. The 87 dB(A) exposure limit accounts for hearing protection; this unprotected-input tool cannot establish compliance with that limit.
Peak sound pressure has separate requirements. This calculator does not assess peaks, weekly exposure, measurement uncertainty, hearing protection or all employer duties. Below an action value does not mean there is no risk.
This is the Great Britain daily-exposure method, not an OSHA TWA calculator. Use competent measurements and the applicable local rules. Local prototype: independent professional review remains part of the release process.
Common questions
What number goes in “Average noise level”?
Enter the measured average A-weighted level for that task, usually labelled LAeq in a noise report. Do not enter a peak or maximum reading. If you do not have the right reading, ask the person responsible for the noise assessment.
What does dB(A) mean?
It is the unit used here to describe noise with a frequency weighting related to human hearing. You only need to copy the correct measured task reading; the calculator handles the maths.
How do I enter 30 minutes or 1 hour 30 minutes?
For 30 minutes, enter 0 in Hours and 30 in Minutes. For 1 hour 30 minutes, enter 1 and 30. No decimal conversion is needed.
Do I need to enter a full eight-hour day?
No. Enter the person’s actual exposure periods, even for a shorter or longer shift. The calculator uses eight hours as a common reference. Include other material noise exposures rather than assuming unentered time is silent.
Should I subtract earmuff or earplug protection?
No. Enter the measured levels before hearing protection. This tool compares the unprotected daily exposure with action values. Hearing-protection performance and the exposure limit require a separate assessment.
Does a result below 80 dB(A) mean everything is safe?
No. It describes only the readings and durations entered. Peak noise, omitted tasks, uncertainty and other duties still need consideration.
Can two tasks happen at the same time?
Do not enter overlapping durations for the same person. When sources operate together, use the combined measured level for that period.
Can I use this for US OSHA noise exposure?
This calculator uses the Great Britain daily-exposure energy method. It is not an OSHA TWA or noise-dose calculator.
Original references
- Control of Noise at Work Regulations 2005, Schedule 1 — single-period and combined daily exposure formula.
- HSE L108: Controlling noise at work — measurement guidance and exposure points.
- HSE: Noise Regulations — action values and exposure limit context.
- HSE exposure calculators and ready-reckoners.
References checked 1 November 2026. HSECalc is independent of the UK Health and Safety Executive.