HML Method Hearing Protection Calculator
The HML method estimates how much hearing protection a worker is actually getting. Enter the H, M and L attenuation values from the protector’s datasheet and the A-weighted (LAeq) and C-weighted (LCeq) noise levels from a workplace noise survey. The calculator returns the level at the ear and the HSE protection rating.
Note: LCeq is the time-averaged C-weighted level. Do not confuse it with the peak C-weighted level (LCpeak), which is usually 20 dB or more higher.
Enter values to see the result
Add the H, M and L values for the protector and the A and C weighted workplace noise levels.
How to Use This Calculator
Enter the protector’s H, M and L values from its datasheet, along with the A-weighted and C-weighted noise levels for the workplace. The C-weighted level here is the time-averaged LCeq, not the peak C level which is usually much higher. The calculator works out the predicted noise reduction (PNR), the protected level at the ear, and the HSE-recommended figure that adds 4 dB for real-world fit.
When to Use the HML Method
The HML method is the middle option in terms of complexity and accuracy. Use it when you’ve got A and C weighted noise data but no octave-band breakdown. It captures more about the shape of the workplace noise than the SNR method, but less than the full octave band method. If you have only a C-weighted level, use the SNR method. If you have full octave-band data, use the octave band method for the most accurate answer.
What the Result Tells You
You’re aiming for a level at the ear between 70 and 80 dB(A). The calculator returns an HSE protection rating in plain English. Below 70 dB(A) means the protector is over-protecting, which can make alarms and communication harder to hear. Above 85 dB(A) means it’s under-protecting, and a higher-attenuation protector or, better, noise reduction at source is needed.
This calculator uses the HML method from BS EN ISO 4869-2 and HSE document L108. It’s intended as a guide.
About Advanced Noise Solutions
Advanced Noise Solutions is a specialist industrial noise consultancy based in St Albans. For 38 years we’ve helped UK manufacturers solve noise problems where they actually start, at the source, rather than wrapping the whole machine in an acoustic enclosure. Our AcoustiFix methodology typically delivers higher dB reductions than enclosures, at a fraction of the cost, with none of the access, visibility or maintenance trade-offs.
If your hearing protector isn’t bringing exposure into the 70 to 80 dB(A) target range, hearing protection alone isn’t the answer. We diagnose the real source of the noise and engineer a fix that brings unprotected exposure down. Get in touch or call us on 01727 864667 to talk it through.