Leq, the equivalent continuous sound level, is the steady level that would deliver the same total sound energy as a noise that varies over the same period. If a street averages an Leq of 72 dBA over an hour, its mix of quiet moments, cars and trucks carries the same energy as a constant 72 dBA tone for that hour. It’s the standard way to express “how loud was it, on average,” and it’s what hearing limits and most noise rules are based on.
The key point is that Leq is an energy average, not an ordinary average of decibel readings. Loud moments count for much more than quiet ones.
Why not just average the decibel readings? #
Because decibels are logarithmic. Suppose a room is at 60 dB for half an hour and 80 dB for the other half. The arithmetic average of the two readings is 70 dB. The energy average is:
10 × log10((10^6 + 10^8) ÷ 2) ≈ 77 dB
The loud half carries 100 times the energy of the quiet half, so it dominates. An arithmetic average would understate the exposure by 7 dB, which under the NIOSH guideline is the difference between about 2.5 hours and about 30 minutes of safe time. For the underlying math, see how decibels add up.
This is why a noise that’s mostly quiet with frequent loud spikes can have a surprisingly high Leq, and why cheap meters that show a simple average can mislead.
How is Leq calculated? #
In words: convert each moment’s level to energy, average the energy over the period, and convert back to decibels.
Leq = 10 × log10( (1/T) × sum of 10^(L/10) over the period )
For equal-length samples, that’s 10 × log10 of the mean of 10^(L/10) across the readings. A digital meter does this continuously, adding up the energy in each short slice of time.
What is LAeq? #
LAeq is simply Leq measured with A-weighting, the frequency curve that approximates human hearing. You’ll also see:
| Term | Meaning |
|---|---|
| Leq | Equivalent continuous level (weighting not stated) |
| LAeq | Equivalent continuous level, A-weighted |
| LAeq,T | LAeq over a stated period, such as LAeq,1h or LAeq,8h |
| LCeq, LZeq | C-weighted or unweighted equivalent level |
| Lnight | LAeq over the night period, used in night-noise guidelines |
| Lden | Day-evening-night level: a 24-hour LAeq with penalties added to evening and night noise |
The WHO’s night noise guideline for Europe, for example, targets an Lnight of 40 dB outside homes. That’s an equivalent continuous level over the night. See dB vs dBA for more on weighting.
How does Leq relate to noise exposure limits? #
NIOSH’s recommended limit of 85 dBA for 8 hours, with a 3 dB exchange rate, is an Leq-based limit. A 3 dB exchange rate is exactly what equal-energy averaging produces: double the energy (+3 dB) for half the time gives the same total. So if your LAeq over an 8-hour shift is 85 dBA, you’re at the NIOSH limit, however the noise was distributed through the day.
OSHA uses a 5 dB exchange rate, which isn’t a pure energy average. Its time-weighted average (TWA) gives loud, short periods less weight than Leq would. That’s one reason the same shift can look acceptable under OSHA and over the limit under NIOSH. See NIOSH vs OSHA noise limits.
Leq vs max vs min: which should you report? #
| Reading | What it tells you | Good for |
|---|---|---|
| Leq | The energy average over the period | Typical level, exposure, comparing rooms or days |
| Max | The loudest time-weighted reading | Individual loud events such as doors, horns, bass hits |
| Peak | The highest instantaneous pressure | Impulse noise such as hammering or gunshots |
| Min | The quietest reading | The background level |
Report Leq for “how loud was it” and max for “how loud did it get.” For sleep and neighbor noise, the max and how often it happens matter alongside the Leq, because sudden events are what wake people. See safe noise level for sleeping.
How long should you measure Leq? #
Long enough to capture a representative sample. For steady noise such as a fan, 30 seconds is plenty. For a busy road, a class or a party, measure several minutes. For exposure over a workday, you need the whole shift or a dosimeter. A short Leq of a varying noise can be misleading if you happened to catch a quiet or loud stretch.
How do you read Leq on a phone? #
Many sound meter apps show only a live number and an arithmetic average. Sound Meter dB shows a true Leq on its stats row, next to min and max and a session timer. Internally, it accumulates every measurement in the energy domain and only converts to decibels for display, as the sound level meter standard defines. Saved sessions keep a per-second Leq timeline, so you can see when the loud stretches happened and export the data as CSV.
Readings from any phone are estimates, since the microphone isn’t a calibrated instrument. The Leq math is the same one a professional meter uses, though. See how accurate phone sound meters are.
Frequently asked questions #
What does Leq stand for? #
Leq stands for “equivalent continuous sound level,” often written L_eq. It’s the constant level that carries the same sound energy as the varying noise measured over the same time.
Is Leq the same as average dB? #
It’s an average, but of sound energy, not of decibel numbers. Because decibels are logarithmic, the energy average is higher than the simple average whenever the level varies, sometimes by many dB.
What is a good Leq for an office? #
It depends on the kind of work, and guidelines vary. Quiet private offices are often in the 40s dBA, and busy open-plan offices with conversation can reach the 60s. For focused work, lower is better, and speech is usually the most distracting part.
Is LAeq the same as TWA? #
Not exactly. LAeq is the energy average over the time measured. TWA expresses exposure as an equivalent 8-hour level. With a 3 dB exchange rate, a TWA is essentially the Leq normalized to 8 hours. OSHA’s TWA uses a 5 dB exchange rate, so it differs from a true Leq.