How to Use the Wall Sound Insulation (STC) Checker
Sound Transmission Class (STC) rates how well a wall blocks airborne sound like speech and TV noise — the higher the number, the quieter it is on the other side. This tool lets you pick from six common US wall assemblies, from a basic single drywall stud wall to a thick concrete party wall or a decoupled double-stud assembly, and see typical published STC ratings and a plain-language sense of how audible sound would be.
A single stud wall with one layer of drywall on each side rates around STC 33, meaning normal conversation next door is often clearly audible. Adding insulation and a second drywall layer pushes that into the high 30s. Multifamily buildings commonly target around STC 50 — achieved with 6-8 inches of concrete or a well-built double-stud wall — where ordinary speech is barely noticeable.
These are general reference values for the wall assembly alone. Real-world sound isolation also depends heavily on doors, windows, electrical outlets, and how carefully penetrations are sealed, so an assembly's lab-tested STC rating is often higher than what you'd actually hear in the field. For a project spec, use manufacturer or lab-tested assembly data.
Frequently Asked Questions
STC (Sound Transmission Class) measures how much a wall reduces airborne sound — the higher the number, the more sound is blocked. Walls in the high-30s let normal speech through faintly, while STC 50+ walls block normal conversation almost completely.
US multifamily codes commonly target around STC 50 for walls between dwelling units, often achieved with 6-8 inch concrete or a well-insulated double-stud assembly. Actual performance still depends on finishes, doors, and construction quality, so treat this as a planning estimate.