Noise Exposure Calculator

How the math works

Allowable time at level L is 8 hours times 2 to the power of (85 − L) over 3, so every 3 dB halves it: 85 dBA allows 8 hours, 88 dBA four, 91 dBA two, 94 dBA one, 97 dBA thirty minutes and 100 dBA fifteen. Dose is your duration divided by the allowable time. The full reasoning lives in the noise exposure guide.

Measure a real average first

Guessing the level defeats the purpose: run the meter for the full noisy period following how to use, or check a phone reading with the phone guide, then paste the Leq here. Compare the result with the decibel chart and the common questions.

Worked examples that stick

Halving is ruthless once you see it. At 85 dBA the allowance is a full 8 hours; at 88 dBA it drops to 4 hours; 91 dBA leaves 2 hours; 94 dBA leaves 1 hour; 97 dBA leaves 30 minutes; 100 dBA leaves 15 minutes. Dose is simply your time divided by that allowance. Two hours at 88 dBA consumes half the day (2 / 4). Thirty minutes at 94 dBA also consumes half (0.5 / 1). Forty-five minutes with an angle grinder averaging 97 dBA blows past a full day (0.75 / 0.5 = 150%). By contrast, four hours in a 76 dBA office plus one hour commuting at 78 dBA barely registers, and anything averaging under 70 dBA needs no dose math at all for the day.

Turn a day into entries, not one guess

Split noisy days into blocks and run each block through the calculator. A woodworker might log 90 minutes of sawing at 92 dBA, 3 hours of shop background at 78 dBA, and 40 minutes of routing at 96 dBA. Enter each average with its own duration, note each dose, then add the percentages: that is your day. A music rehearsal at 101 dBA for 20 minutes already passes 100% on its own (allowance near 12 minutes), so earplugs or distance are the only levers — stepping back doubles distance and trims roughly 6 dB outdoors. Concerts, mowing, track work and open-plan sanding all behave the same way: short, loud blocks dominate the total.

Get a Leq worth calculating with

Open the meter and measure the actual task for its full span, following how to use. Use A-weighting with Slow response, hold the phone at ear height with the mic uncovered, stay quiet during the run, and read the Leq over at least 30 to 60 seconds — longer when the sound surges and dips, like a classroom or a cafe lunch rush. Calibrate that phone against a known reference at the same spot first, keep the same case and settings, and never reuse another device's offset. Below around 30 dBA the mic floor reads high and near 95 to 100 dBA it clips, so treat garage-band peaks as screening hints. The phone guide and decibel chart help you sanity-check the average before you paste it here.

Mistakes that bend your percentage

• Typing the maximum instead of the Leq — a 102 dBA drum hit inside an 88 dBA rehearsal does not make the whole hour 102 dBA.
• Measuring ten seconds from a pocket and calling it a shift average; fabric alone can swing the reading by double digits.
• Mixing C-weighted bass peaks into an A-weighted dose, or measuring a subwoofer at 30 cm and applying it to a sofa 3 metres away.
• Treating a screening percentage as proof for a workplace file or a complaint — formal findings need Class 1 or 2 gear, as the noise exposure guide and common questions explain.

Noise exposure guide → · What a sound level meter is →