How the calculator works
Every noise rule rests on the same idea: your ears can cope with a certain amount of sound energy per day. A level of 85 dB(A) for 8 hours uses up the whole daily allowance under NIOSH guidance, which is 100% dose. Go louder and the allowance runs out faster.
- NIOSH (the US National Institute for Occupational Safety and Health) uses an 85 dB(A) limit over 8 hours with a 3 dB exchange rate: every 3 dB louder halves the safe time. This follows the physics, because +3 dB is double the sound energy. UK and EU workplace rules use the same 3 dB maths.
- OSHA (the US workplace regulator) uses 90 dB(A) over 8 hours with a 5 dB exchange rate. It's a legal minimum for US employers, and more lenient than NIOSH at high levels.
The calculator adds up the dose from each activity you enter and converts it back into a single 8-hour average level, called the daily personal noise exposure (LEX,8h) in the UK and the time-weighted average (TWA) in the US.
Safe listening times at a glance (NIOSH)
| Level | Safe time per day |
|---|---|
| 85 dB(A) | 8 hours |
| 88 dB(A) | 4 hours |
| 91 dB(A) | 2 hours |
| 94 dB(A) | 1 hour |
| 97 dB(A) | 30 minutes |
| 100 dB(A) | 15 minutes |
| 103 dB(A) | 7.5 minutes |
| 106 dB(A) | under 4 minutes |
| 110 dB(A) | about 1.5 minutes |
Ear defenders and earplugs reduce the level reaching your ears, but real-world protection is usually well below the number on the packet, because of fit.
Where do the levels come from?
You can type a level from our decibel chart, but your own environment is the best source. The Decibel Meter app shows your noise dose live using NIOSH or OSHA rules, along with the 8-hour TWA so far, so you don't need to estimate anything.
This calculator is for general information and planning. It isn't a workplace noise assessment. In the UK, employers must assess noise risks under the Control of Noise at Work Regulations 2005, and the HSE has its own exposure calculators for that purpose. If your ears ring after loud noise, or you notice muffled hearing that doesn't clear, see a GP or audiologist.
Read more: how loud is too loud? and workplace noise limits in the UK and US.
