Measurements · Noise
Equivalent Continuous Level (Leq)
Also known as average noise level, equivalent continuous sound level
Equivalent continuous sound level (time-averaged energy), the core occupational-noise metric.
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What it is
What is Leq (equivalent continuous sound level)?
Leq is the single most important metric in environmental and occupational noise monitoring. Real-world noise is constantly fluctuating (traffic passes, machines cycle, voices rise and fall), so a single instantaneous decibel reading tells you little. Leq solves this by expressing the equivalent continuous level: the steady sound level that would deliver the same total acoustic energy over the measurement period as the actual varying noise did. In effect it averages the energy, not the decibels, so a few loud events count heavily. It is almost always A-weighted (written LAeq) to reflect how the human ear responds to frequency.
Because it captures total exposure in one number, Leq underpins nearly every noise limit and assessment.
Band resolution: reported broadband plus 1/1 octave and 1/3 octave. The metric and its frequency band are independent. Check the sound-capable devices below for what each one reports.
Health and operational effects
Sustained noise exposure damages hearing irreversibly, and beyond the ears it disturbs sleep, raises stress and blood pressure, impairs concentration and learning, and generates the complaints that drive planning disputes and enforcement. Occupational noise causes one of the most common and most preventable workplace injuries; environmental noise around construction, industry, transport, and entertainment venues is a persistent community-health and nuisance issue.
For site operators, employers, and event organizers, Leq is the number in the permit, the risk assessment, and the complaint file. Managing it is both a legal duty and a community-relations task.
Limits
Equivalent Continuous Level (Leq) Limit Values
The published values, by averaging period; each links to the standard that sets it.
Lden, road traffic
Lnight, road traffic
Lden, railway
Lnight, railway
Lden, aircraft
Lnight, aircraft
Lden, wind turbines
LAeq,24h yearly average, leisure noise
- WHO noise 2018 45 dB: conditional recommendation
- WHO noise 2018 70 dB: all leisure sources combined
Leq is reported in decibels (dB, or dB(A) when A-weighted) over a stated period. The averaging time is part of the metric, so a 15-minute LAeq and a 12-hour LAeq are different quantities. Occupational limits (such as an 85 dB(A) daily exposure action value) and environmental limits are both expressed through Leq and related indices. Interpret it as an energy average: a short burst of loud noise raises Leq far more than its brief duration suggests, which is why a handful of loud events can push a long-period Leq over its limit.
How it is measured
How Equivalent Continuous Level (Leq) Is Measured
Leq is computed by a sound level meter or noise monitor built to the IEC 61672 standard, which defines Class 1 (precision) and Class 2 (general-purpose) instruments. The microphone captures the fluctuating sound pressure, the instrument applies A-weighting and integrates the energy over the set period to produce Leq, alongside related metrics such as Lmax (loudest level), Lpeak (peak pressure, important for impulsive noise), and statistical levels like L90 (the background) and L10 (the intrusive level). For unattended environmental monitoring, instruments log Leq continuously over days or weeks with weather protection on the microphone.
Built into Aethair PRO1
Measured by the monitor's own sensors, calibrated before it ships: nothing to add.
An instrument on Thiamis2
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing noise monitors
For environmental and boundary monitoring, place the microphone at the position of the affected receptor or the site boundary, at a standard height and clear of reflecting surfaces that would inflate the reading, with a windshield fitted since wind noise corrupts measurements. For occupational assessment, a noise dosimeter is worn near the worker's ear to capture personal exposure. Because measured Leq depends heavily on distance and screening, consistent, standard-compliant positioning is essential for defensible results.
Every device and option that measures Equivalent Continuous Level (Leq) 3
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
Aethair PRO built-in sensors | Built-in sensors | Aethair PRO | Equivalent Continuous Level (Leq)Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1 |
 Cirrus Research · 151B, 152B, 151A… | Noise Monitors | Thiamis | |
 TSI · SP-SE-1, SP-SE-1-1/1, SP-SE-1-1/3… | Noise Monitors | Thiamis | Equivalent Continuous Level (Leq)Average Level (Lavg)Max Level (Lmax)Min Level (Lmin)Peak Level (Lpeak)Sound Pressure Level (SPL)TWA / Noise Dose |
Where it is monitored
Solutions That Monitor Equivalent Continuous Level (Leq)
Each one links to the solution page showing what that industry measures it for.
Cabin Air Quality
Core parameterMining and quarrying are persistently noisy (drilling, blasting, crushing, and heavy haulage).
Noise Monitoring
Core parameterEnvironmental noise assessment, whether for planning, industry, transport, or entertainment venues, is built on the equivalent continuous level (Leq) measured against limits at the affected receptor.
Perimeter Monitoring
Core parameterConstruction noise, expressed as the equivalent continuous level (Leq), is regulated at the site boundary in most permits because equipment, breakers, and haul trucks carry sound far beyond the site fence.
Article Library
Reading on Equivalent Continuous Level (Leq)
Air Quality Near Data Centers: What Communities Should Know
Air quality near data centers: construction dust, diesel generator emissions, and noise, and how communities get independent monitoring data.
Data Center Air Quality Monitoring, Inside and Out
Data center air quality monitoring for operators: ISO 14644 cleanliness in the white space, construction dust, generator emissions, and perimeter noise.
Related
More in Noise
Questions
Equivalent Continuous Level (Leq) FAQ
Why use Leq instead of just measuring decibels?
Because real noise fluctuates constantly, a single decibel reading is meaningless for exposure. Leq gives the equivalent steady level with the same total energy over the period, capturing the cumulative impact of a varying sound in one comparable number, which is why noise limits are written in terms of Leq rather than instantaneous levels.
What is the difference between Leq, Lmax, and Lpeak?
Leq is the energy-average level over the whole period; Lmax is the highest level reached (with a time weighting); Lpeak is the true instantaneous peak sound pressure, important for sudden impulsive noise like impacts or gunfire. A full assessment reports several together because they answer different questions about the same noise.
What does Class 1 versus Class 2 mean?
These are IEC 61672 accuracy grades for sound level meters. Class 1 (precision) has tighter tolerances and is required for many regulatory and legal assessments; Class 2 (general-purpose) is adequate for routine surveys and screening. The right class depends on what the measurement will be used for.
How do I monitor environmental or workplace noise?
Pair a Thiamis gateway with an IEC 61672 sound level meter or noise dosimeter for continuous, weatherproofed logging of Leq and related metrics. Use the configurator to combine noise with PM10 and PM2.5 in a construction-site configuration, since dust and noise are usually permitted and monitored together.
Monitor Equivalent Continuous Level (Leq) on the Record
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