Day-Night Average Sound Level (Ldn) Calculator
The day-night average sound level, Ldn, condenses a full day of noise into a single value in decibels. This calculator takes two equivalent levels, a daytime Leq (Ld) for 07:00 to 22:00 and a nighttime Leq (Ln) for 22:00 to 07:00, and returns Ldn to one decimal place.
Night hours carry a 10 dB penalty: 10 dB is added to Ln before the periods are combined. The two levels are then energy averaged over 24 hours, weighting 15 day hours and 9 night hours:
Built for urban planners and acoustic consultants who already have period levels from measurement or prediction, the tool shows the formula with your values substituted, so every result can be checked by hand.
Calculate Ldn
Day-night average sound level, Ldn
—dB
How to use the calculator
- Enter the daytime equivalent level Ld in dB, covering 07:00 to 22:00 (15 hours).
- Enter the nighttime equivalent level Ln in dB, covering 22:00 to 07:00 (9 hours). Do not add the 10 dB penalty yourself; the calculator applies it.
- The result updates as you type. You can also press Calculate.
- Read Ldn in dB to one decimal place, and check the formula line, which shows your typed values substituted into the equation.
Frequently asked questions
What is the day-night average sound level Ldn?
The day-night average sound level, symbol Ldn, is the 24-hour average sound level in decibels obtained after adding 10 dB to the sound levels of the night hours, 22:00 to 07:00.
Which hours do Ld and Ln cover?
Ld is the daytime equivalent level from 07:00 to 22:00, which is 15 hours. Ln is the nighttime equivalent level from 22:00 to 07:00, which is 9 hours. The calculator adds 10 dB to Ln before it averages the two periods.
Why is Ldn not the simple average of Ld and Ln?
Decibel levels are logarithmic, so the calculator converts each level to relative energy, weights it by its hours, averages over 24 hours and converts back to decibels. With the 10 dB night penalty, Ld 55 dB and Ln 55 dB give an Ldn of 61.4 dB, not 55 dB.
Can I enter 0 dB or a negative level?
Yes. 0 dB and negative levels are valid inputs. Each level must be from -50 dB to 250 dB; a value outside that range shows an error and no result is calculated.
Disclaimer
This calculator gives an estimate only and is not a substitute for a qualified engineer.
The day-night average sound level (symbol Ldn) is the 24-hour average sound level in decibels obtained after adding 10 dB to the sound levels of the night hours, 22:00 to 07:00 (source: 14 CFR 150.7, definition of day-night average sound level, 2010 edition). The formula used here is the energy average over 24 hours of 15 day hours and 9 night hours with that penalty. It uses no hourly breakdown and no evening period.