What is an STC - Sound Transmission Class?

The numerical rating of a material's ability to block sound transmission.


An STC, or Sound Transmission Class, rating is a standardized measurement used across the construction and interior design industries to quantify how well a building material is able to prevent sound from passing through it. This measurement is crucial for ensuring privacy and minimizing noise disruption in both residential and commercial spaces. The higher the STC rating, the more effective the material is at blocking sound.

To determine the STC rating, a sample of the material is placed in a laboratory setting where it is subjected to a range of frequencies typically found in human speech (125 to 4000 Hz). The sound levels on both sides of the material are measured, and the results are used to calculate the STC rating. This process allows for consistent comparisons between different materials and provides a reliable metric for architects, designers, and builders when selecting materials for sound insulation.

STC ratings are especially important in multi-unit housing, hotels, office buildings, and any environment where controlling sound transmission is critical. They play a significant role in the selection of windows, doors, walls, and flooring materials. Understanding and utilizing STC ratings can greatly enhance the comfort, privacy, and usability of a space.


For example, when designing a conference room in an office building, an interior designer might specify a wall with a high STC rating to ensure conversations remain confidential and are not disturbed by noises from adjacent areas. Similarly, in a residential apartment complex, specifying doors with adequate STC ratings can greatly reduce noise transmission from common areas into individual living spaces.


  • How is the STC rating determined?

    The STC rating is determined by measuring the ability of a material to block sound at frequencies between 125 to 4000 Hz in a laboratory setting. The sound levels on both sides of the material are measured, and these measurements are used to calculate the rating.

  • What is considered a good STC rating?

    A good STC rating varies depending on the application but generally, ratings between 50 to 60 are considered good for preventing speech from being audible. Higher ratings indicate better sound-blocking capabilities.

  • Can STC ratings be applied to all materials?

    STC ratings are primarily applied to materials used in building construction such as walls, floors, doors, and windows. However, not all materials are rated; the rating is most relevant for those intended to provide sound insulation.

  • How can I improve the STC rating of a space?

    Improving the STC rating of a space can be achieved by adding mass, using sound-absorbing materials, and employing construction techniques designed to decrease sound transmission. This might include adding additional layers of drywall, using specialized insulation, or installing soundproof windows and doors.

Practical Application

In practice, understanding and applying STC ratings is essential for creating spaces that are both functional and comfortable. When embarking on a construction or renovation project, consider the requirements of each space and choose materials with STC ratings that meet or exceed these needs. This will ensure that sound is properly managed, enhancing the occupant experience and usability of the space.