Noise Reduction Coefficient Calculator

Analyze sound flanking transmission paths. Input the STC of the direct path and each flanking path (walls, floor, ceiling) to find the apparent STC and weakest link.

Inputs

Direct path STC

Flanking wall 1 STC

Flanking wall 2 STC

Flanking floor STC

Flanking ceiling STC

Tab to move between fields

Results

Apparent STC

47.4

Flanking penalty (dB)2.6

Weakest path (0-4)0

Weakest path contribution (%)54.6

Max achievable STC50

Improvement potential (dB)2.6

How to Use This Calculator

Enter Direct path STC, Flanking wall 1 STC, and Flanking wall 2 STC.
Set Flanking floor STC and Flanking ceiling STC.
Review the Apparent STC result.
Use Flanking penalty (dB) and Weakest path (0-4) to inform your decision.

How the result changes with Direct path STC

Direct path STC	Apparent STC
26	26
41	40.6
59	50.2
74	50.8

What each input means

Direct path STC: STC rating of the primary separating wall or floor assembly (the direct sound path).
Flanking wall 1 STC: STC of the first flanking wall path (sound traveling through the side wall around the partition).
Flanking wall 2 STC: STC of the second flanking wall path (opposite side wall).
Flanking floor STC: STC of the floor flanking path (sound traveling through or under the floor).
Flanking ceiling STC: STC of the ceiling flanking path (sound traveling through or above the ceiling plenum).

What each result means

Apparent STC: Combined STC considering all transmission paths. Always lower than the direct path STC.
Flanking penalty (dB): How many STC points are lost due to flanking paths (direct STC minus apparent STC).
Weakest path (0-4): Path transmitting the most sound. 0 = Direct, 1 = Wall 1, 2 = Wall 2, 3 = Floor, 4 = Ceiling.
Weakest path contribution (%): Percentage of total transmitted sound energy coming through the weakest path.
Max achievable STC: Maximum apparent STC if all flanking were eliminated (equals the direct path STC).
Improvement potential (dB): Possible dB improvement if all flanking paths were perfectly treated.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Direct path STC = 50, Flanking wall 1 STC = 55, Flanking wall 2 STC = 55, Flanking floor STC = 60 = 5 input(s) provided
Calculate Apparent STC
Apparent STC = -10 * log10(tauTotal)
47.4 = 47.4
Calculate Flanking penalty
Flanking penalty = directSTC - apparentSTC
2.6 = 2.6
Calculate Weakest path
Weakest path
0 = 0

Engine last updated July 28, 2026. Checked against 2 independently-derived tests — how we verify calculators.

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Acoustics

STC Rating Calculator

Estimate Sound Transmission Class (STC) for wall assemblies based on wall type, drywall layers, insulation, stud spacing, resilient channel, and staggered studs.

Acoustics