How noise is measured

Why and how is the noise around airports measured?

The noise from planes is measured for many reasons. It is important to know whether the noise levels are going up or down over time, and if so, by how much.  

In Britain, this noise is measured by averaging out the noise levels during the day (a 16-hour day) during the summer period. The amount of noise is given in decibels (dB). This averaging-out means that the day’s high and low levels are levelled out to give a single figure. The Government calls this averaged decibel measurement ‘LAeq’, and this is the most common international measure of aircraft noise. As a measurement, it means ‘equivalent continuous noise level’.

What’s the average noise level near you?

In the UK, Government research indicates that people start being concerned by aircraft noise at 57dB, averaged over 16 hours (57dB LAeq). They use this as the starting point in airport and aircraft noise policies.

To show where the different average noise levels are around the airport, the Government has developed maps showing ‘noise contours’. Below is the ‘noise contour map’ for the area around Gatwick. The contours are an irregular shape because you get more noise at the ends of the runway (where planes take off and land) than at the sides.

The map here shows the contours for 2013, combining noise for all flights, regardless of the wind direction and therefore of the direction the planes were flying.

We produce a number of community reports for where our noise monitors are located. Read your local report here.

How many people are affected?

In the last 20 years the 57dB noise contour has shrunk. This is because aircraft are quieter than they used to be. As a result the number of people who live within this noise contour has reduced. 

In 1993, there were 14,600 people in the 57dB noise contour around Gatwick. By 2011 this had reduced to 3,050. This is despite a rapid growth in air travel at the same time, from around 191,000 flights a year in 1993 to 244,741 in 2011.