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.

Inputs

Wall type (0-3)

Drywall layers per side

Insulation type (0-3)

Stud spacing (inches)

Resilient channel (0=no, 1=yes)

Staggered/double studs (0=no, 1=yes)

Tab to move between fields

Results

Estimated STC

Base STC (wall type only)33

Drywall bonus (pts)0

Insulation bonus (pts)0

Decoupling bonus (pts)0

Assembly grade (0-3)0

Improvement potential (pts)17

Est. fire rating (min)30

How to Use This Calculator

Enter Wall type (0-3), Drywall layers per side, and Insulation type (0-3).
Set Stud spacing (inches), Resilient channel (0=no, 1=yes), and Staggered/double studs (0=no, 1=yes).
Review the Estimated STC result.
Use Base STC (wall type only) and Drywall bonus (pts) to inform your decision.

What each input means

Wall type (0-3): 0 = Wood stud, 1 = Steel stud, 2 = Concrete block (CMU), 3 = Poured concrete.
Drywall layers per side: Number of gypsum board layers on each side (1 = standard, 2 = double layer, 3 = triple).
Insulation type (0-3): 0 = None, 1 = Fiberglass batt, 2 = Mineral wool (Rockwool), 3 = Spray foam. Mineral wool is best for sound.
Stud spacing (inches): On-center stud spacing in inches. 24" OC is slightly better acoustically.
Resilient channel (0=no, 1=yes): Whether resilient channels are used to decouple drywall from studs. Major STC improvement for stud walls.
Staggered/double studs (0=no, 1=yes): Staggered studs on a wider plate or double-stud wall with air gap. Best decoupling method.

What each result means

Estimated STC: Estimated Sound Transmission Class rating for the assembly. STC 50+ recommended between dwellings.
Base STC (wall type only): STC of the bare wall type with minimal treatment.
Drywall bonus (pts): STC points gained from additional drywall layers.
Insulation bonus (pts): STC points gained from cavity insulation.
Decoupling bonus (pts): STC points gained from resilient channel and/or staggered studs.
Assembly grade (0-3): 0 = Basic (<38), 1 = Improved (38-44), 2 = Good (45-54), 3 = Premium (55+).
Improvement potential (pts): Estimated STC points available through recommended upgrades.
Est. fire rating (min): Rough fire resistance estimate based on drywall layers (30 min or 60 min).

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Wall type (0-3) = 0, Drywall layers per side = 1, Insulation type (0-3) = 0, Stud spacing (inches) = 16 = 6 input(s) provided
Calculate Estimated STC
Estimated STC
33 = 33
Calculate Base STC
33 = 33
Calculate Drywall bonus
Drywall bonus
0 = 0

Engine last updated July 28, 2026. Checked against 3 independently-derived tests — how we verify calculators.

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