Noise Dose Calculator

A level says how loud something is at one moment. A dose says what staying there costs. NIOSH draws the distinction itself: a sound level at a given point in time can be higher than the exposure limit without creating risk, provided it is balanced out by enough time at lower levels during the dayNIOSH.

That single sentence is why a decibel figure on its own settles nothing, and why this page asks for two numbers instead of one.

What the calculator is doing

Each period costs the share of its own allowance that it uses. Add the shares together and you have the day. NIOSH publishes the anchor: eight hours at 85 dBA reaches 100% of the daily noise doseNIOSH. Everything else falls out of the exchange rate, which is the part most people get wrong.

Sound energy doubles every 3 dB. So the allowed time halves every 3 dB, and NIOSH's own worked example is that a level of 88 dBA leaves four hours rather than eightNIOSH. Three decibels reads like a rounding error. On a dose it is half the day.

Two hours at 91 dBA is a full day's allowance. So is one hour at 94 dBA, and so is a quarter of an hour at 100 dBA. Once you have spent it, the rest of the day has to happen below the line — and most days are not arranged that way.

A day, worked through

Take an afternoon that sounds unremarkable. Ninety minutes behind a mower at 85 dBA is three-sixteenths of the allowance, since the allowance at that level is the full eight hours. Twenty minutes with a chain saw at 95 dBA is another four-tenths: at 95 dBA the allowance has fallen to roughly three-quarters of an hour. Two hours at a gig at 100 dBA — where fifteen minutes is the whole allowance NIOSH publishesNIOSH — is eight days' worth.

Add those and the afternoon lands near nine hundred percent, of which the mower, the part that felt loud enough to complain about, contributed about two. That inversion is the reason to add a day up rather than judge it by its worst moment. The loudest thing you noticed is rarely the thing that spent the day.

It also shows what moves the answer. Halving the time at the gig halves the dose. Finding a spot three decibels quieter does the same. Neither is a dramatic change, and both shift the total further than anything that happens at the quiet end of the afternoon.

Where these numbers come from

The model is NIOSH's recommended exposure limit, set in 1998 at 85 dBA as an eight-hour time-weighted average, with exposures at or above that level considered hazardousNIOSH. The 3 dB exchange rate is sometimes called the equal-energy rule, because that is what it is: the arithmetic follows the energy rather than a policy compromiseNIOSH.

One caveat belongs at the top rather than buried at the bottom. The REL is an occupational limit. NIOSH says plainly that it is not a recommendation for noise in the general environment, and that it assumes the other sixteen hours of the day are spent in quieter conditionsNIOSH. Borrowing it for a Saturday spent mowing and then at a gig is useful — it is the best-documented model there is for the trade-off between level and time — but it is a borrowing, and the number it produces is a guide, not a finding about your hearing.

A different agency draws a different line, with a different exchange rate and a different starting point. Which one applies to a workplace is a question about regulation rather than about physics, and it belongs with the NIOSH vs OSHA limits rather than here.

Why nothing counts below 80 dBA

The calculator stops counting under 80 dBA, and that floor is worth explaining because it is not a figure NIOSH prints. Its published table starts at 85 dBA for eight hours and works upwardNIOSH. Run the exchange rate downward instead and the allowance at 80 dBA comes to more than twenty-five hours — longer than the day it is supposed to fit inside. A quiet office cannot reach a full dose no matter how long you sit in it, so counting a fraction of a percent for it would suggest a cost that the model does not actually claim.

That is also why a long day can produce a small figure. The calculator prints the total minutes and the counted minutes separately: six hours in a room at 70 dBA and forty minutes with a chain saw is six hours and forty minutes of your life, and forty minutes of dose.

What a figure over 100% means, and what it does not

It means the day, as described, spends more than the allowance the NIOSH model sets aside — and that hearing protection, distance, or less time is the sensible response. NIOSH's own advice for anyone seeing 85 dBA or more on a readout is to take precautions regardless of whether the average is knownNIOSH.

It does not mean damage has occurred. Noise-induced hearing loss is cumulative and depends on how loud, how long, how much rest the ears get in between, and on the listener — the risk is not a threshold that trips at 101%NIOSH. Nor is it a compliance determination. Nothing on this page is an IEC 61672 result, and none of it should be used for a legal, occupational or medical decision.

Using your own levels

The presets above are the figures NIDCD and NIOSH publish for common sources, entered at the lower end of each published range so a range straddling a threshold lands in the gentler bandNIDCD. They are typical values for a category of thing, not for your mower or your venue.

For the room you are actually in, you can measure dB in your browser and put the figure into the level column. Two things about that number are worth carrying over. It is an uncalibrated estimate, and smartphone sound apps have been found to sit within roughly ±10 dB of a reference instrumentKardous & Shaw. On a dose, 10 dB is a factor of ten in allowed time, so a plan built on a single uncalibrated figure is a rough plan. It is still a better one than a figure with no duration attached to it at all.

The other thing is that a dose wants an average over a period, not a peak. If the level swings, use something near the middle of what the readout sat at, not the loudest thing it caught. The meter's own Leq does this for a live session; for a period you are estimating from memory, a middling figure is closer than the worst one.

When the number is for someone else

A dose figure is at its most useful when it is written down at the time rather than reconstructed afterwards. If the noise belongs to someone else — a neighbour, a landlord, a venue — a dated noise complaint log of levels and durations is worth more than a single dramatic reading, because it is the duration that turns a loud moment into an exposure.

Most of the argument on this page rests on one figure, the 85 dBA action level, and on one rule about what happens for every 3 dB above itNIOSH. If you take nothing else away: the level tells you how loud, and only the clock tells you whether it matters.