Sound Insulation Calculator
STC improvement from insulation type in wall assembly.
About this calculator
This calculator estimates the Sound Transmission Class (STC) rating of a wall assembly after adding soundproofing treatments, and translates that rating into an approximate perceived-loudness reduction. Wall assembly is the input with the largest effect: switching from a bare single 2×4 wall (STC 33) to a double 2×4 wall with an air gap (STC 50) moves the baseline by 17 points before any treatment is applied — more than double the swing available from choosing among the six insulation types (a 7-point spread between mineral wool and no insulation). Insulation type, resilient channel, Green Glue compound, and an extra drywall layer each add their own STC bump, but the engine applies diminishing returns once more than one treatment is stacked: the combined boost is multiplied by a factor between 0.85 and 1.0 rather than summed at full value, reflecting that real assemblies don't get the full benefit of every add-on simultaneously.
Perceived noise reduction is derived from STC improvement alone, on the rule of thumb that every 10 STC points sounds roughly half as loud. Wall area only scales the material cost estimate — it has no effect on the acoustic rating itself. The estimate is a design-stage approximation based on published assembly ratings, not a substitute for a lab-tested STC number or an acoustical consultant's flanking-path analysis.
Inputs
Results
Final STC rating
40
Perceived noise reduction
38%
How to Use This Calculator
- Pick the Wall assembly closest to your framing — it sets the Base STC and moves the final rating more than any single treatment.
- Choose an Insulation type; mineral wool adds the most STC, closed-cell spray foam the least.
- Toggle Resilient channel, Green Glue compound, and an extra drywall layer on or off to see their combined (diminishing-returns) effect.
- Enter Wall area to size the material cost estimate — it does not change the STC rating.
- Review Final STC rating and Perceived noise reduction, then check Material cost for the selected treatments.
What each input means
- Wall assembly
- Base wall framing and sheathing type.
- Insulation type
- Cavity insulation. Mineral wool is best for sound; closed-cell foam is worst.
- Resilient channel
- Metal channels that decouple drywall from studs (+6 STC). Very effective.
- Green Glue compound
- Viscoelastic damping compound between drywall layers (+4 STC).
- Add extra drywall layer
- Second layer of drywall adds mass (+5 STC). Best with Green Glue.
- Wall area
- Total wall area to soundproof.
What each result means
- Base STC (before treatments)
- Starting STC rating of the wall assembly alone.
- Final STC rating
- Achieved STC after all treatments. STC 50+ is recommended between units.
- STC improvement
- Total STC points gained from treatments.
- Perceived noise reduction
- Approximate perceived loudness reduction. Every 10 STC sounds half as loud.
- Material cost
- Estimated material cost for selected treatments.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersWall assembly = 0, Insulation type = 2, Resilient channel = 0, Green Glue compound = 0 = 6 input(s) provided
- Calculate Final STC ratingFinal STC rating40 = 40
- Calculate Perceived noise reductionPerceived noise reduction38 = 38
- Calculate Base STCBase STC33 = 33
- Calculate STC improvementSTC improvement7 = 7
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What has the single biggest effect on the final STC rating?
Wall assembly. The five framing options span STC 33 to STC 50 — a 17-point range — before any insulation or treatment is added. That's more than double the 7-point spread between the best insulation (mineral wool, +7) and the worst (closed-cell spray foam, +2), so upgrading the underlying wall construction matters more than any single add-on treatment.
If I add resilient channel, Green Glue, and an extra drywall layer, do I get the full +15 STC?
No. The calculator adds full value for a single treatment, but once more than one treatment is combined it multiplies the total by a diminishing-returns factor between 0.85 and 1.0 rather than summing every boost at face value. Stacking treatments still helps, just not as much as adding their individually advertised STC ratings would suggest.
Why doesn't changing Wall area affect the Final STC rating?
Wall area only feeds the material cost estimate — it multiplies the selected treatments' per-square-foot cost to get a total dollar figure. The STC rating comes entirely from the wall assembly, insulation type, and treatment toggles, so a 10 square-foot closet and a 500 square-foot wall with identical construction get the same acoustic rating.
What does the Perceived noise reduction percentage actually mean?
It converts the STC improvement into an approximate loudness change using the rule that every 10 STC points sounds about half as loud to the human ear. A 7-point STC improvement (mineral wool alone) computes to roughly a 38% perceived loudness reduction, even though the STC scale itself only moved 7 points.
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