Ldn / CNEL Community Noise Calculator

Q: What is Ldn, the day-night average sound level?

Ldn (also written DNL) is the A-weighted average sound level over 24 hours, with a 10 dB penalty added to every nighttime hour (10pm to 7am) to account for greater sensitivity to noise while sleeping. It is the metric the U.S. EPA, HUD, and the FICON use to judge community noise and residential land-use compatibility.

Q: What Ldn level is acceptable for residential land use?

HUD's site-acceptability standard (24 CFR Part 51) treats 65 dB Ldn or below as Acceptable, above 65 up to 75 dB as Normally Unacceptable, and above 75 dB as Unacceptable. Many local ordinances and the FICON use the same 65 DNL threshold for residential compatibility, so above 65 dB Ldn a project typically needs noise mitigation or a special approval.

Enter the average daytime, evening, and nighttime sound levels at a property line or receptor. This tool computes the day-night average sound level (Ldn / DNL) or the California CNEL, applying the +10 dB night and +5 dB evening penalties, and flags it against the HUD 65 dB Ldn guideline for residential land use used by EPA, HUD, and FICON.

Method reviewed by CSTI's INCE Board-Certified engineers

Community noise inputs

Enter A-weighted average sound levels (dBA) for each daily period. The night and evening penalties are applied automatically.

Daytime Ld = 7am–10pm (15 h). Nighttime Ln = 10pm–7am (9 h, +10 dB penalty).

Daytime average — Ld (dBA)

Nighttime average — Ln (dBA), 10pm–7am

Result

Ldn (DNL) · HUD 65 dB residential guideline

Ldn

62.6dB

Near limit

vs HUD 65 dB

−2.4dB

Within 5 dB

The method (EPA / HUD / FICON)

Ldn = 10·log₁₀[ (1/24)( 15·10^(Ld/10) + 9·10^((Ln+10)/10) ) ] (day 15 h · night +10 dB)

CNEL = 10·log₁₀[ (1/24)( 12·10^(Ld/10) + 3·10^((Le+5)/10) + 9·10^((Ln+10)/10) ) ] (evening +5 dB · night +10 dB)

Worked example: Ld = 60 dBA (day), Ln = 55 dBA (night), Ldn mode. Day term = 15·10^(60/10) = 1.5×10⁷. Night term = 9·10^((55+10)/10) = 9·10^6.5 = 2.846×10⁷. Sum = 4.346×10⁷; ÷ 24 = 1.811×10⁶. Ldn = 10·log₁₀(1.811×10⁶) = 62.6 dB — HUD-acceptable, but only 2.4 dB under the 65 dB residential guideline. Daytime is 7am–10pm (15 h) for Ldn and 7am–7pm (12 h) for CNEL; night (10pm–7am, 9 h) always carries a +10 dB penalty. A monitored measurement per ANSI S12.9 gives the defensible number of record — this estimate sizes the exposure. See HUD 24 CFR Part 51 and the EPA Levels Document.

Frequently asked

What is Ldn, the day-night average sound level?

Ldn (also written DNL) is the A-weighted average sound level over 24 hours, with a 10 dB penalty added to every nighttime hour (10pm–7am) to account for greater sensitivity to noise while sleeping. It is the metric the U.S. EPA, HUD, and the FICON use to judge community noise and residential land-use compatibility. This Ldn calculator combines your daytime and nighttime averages into the single day-night average sound level.

What is the difference between Ldn (DNL) and CNEL?

Both are 24-hour, penalty-weighted averages. Ldn/DNL splits the day into daytime (7am–10pm) and night (10pm–7am, +10 dB). CNEL — the Community Noise Equivalent Level used in California CEQA and airport-noise work — adds a separate evening period (7–10pm) with a +5 dB penalty and shortens daytime to 7am–7pm. For the same environment CNEL is usually within about 1 dB of Ldn, and slightly higher. Toggle this CNEL calculator to compare the two.

What Ldn level is acceptable for residential land use?

HUD's site-acceptability standard (24 CFR Part 51) treats 65 dB Ldn or below as “Acceptable,” above 65 up to 75 dB as “Normally Unacceptable,” and above 75 dB as “Unacceptable.” Many local ordinances and the FICON use the same 65 DNL threshold for residential compatibility. Above 65 dB Ldn, a project typically needs noise mitigation or a special approval.