Soundproofing Calculator
Estimate how much noise passes through a wall based on STC rating. Enter the source noise level, select a wall type, and optionally set a target noise level to see if your wall construction meets your goals.
Estimated noise on the other side — Quiet
Soundproofing Calculator: Understanding STC Ratings and Noise Reduction
Whether you are building a home studio, a home theater, or simply trying to reduce noise between rooms, understanding how sound travels through walls is an essential first step. Soundproofing relies on mass, decoupling, absorption, and sealing, but quantifying the result starts with a single number: the Sound Transmission Class (STC) rating. This calculator uses your wall's STC rating and your source noise level to estimate how much sound passes through to the other side.
What Is STC Rating?
Sound Transmission Class (STC) is a numerical rating of how well a building partition such as a wall, floor, or ceiling attenuates airborne sound. The rating is determined by laboratory testing across a range of frequencies from 125 Hz to 4,000 Hz. A higher STC number indicates greater sound reduction. The scale is relative: each additional 10 STC points roughly corresponds to a perceived halving of loudness.
STC ratings are widely used in building codes and architectural specifications. A standard wall with a single layer of drywall on each side of wood studs typically achieves around STC 33. Code minimums for party walls between dwelling units in the US are generally STC 45 or higher, while high-performance assemblies used in recording studios can reach STC 65 or above.
How the Calculation Works
The simplified model used in this calculator subtracts the wall's STC rating from the source noise level in decibels. For example, if a television produces 65 dB and your wall is rated STC 40, the estimated transmitted noise on the other side of the wall would be 65 minus 40, which equals 25 dB — near the threshold of silence. While this is a useful approximation, real-world results depend on many additional factors.
The decibel scale is logarithmic. A 10 dB increase corresponds to roughly twice the perceived loudness, while a 3 dB difference is just barely perceptible. This means that improving your wall from STC 33 to STC 43 is a substantial improvement in perceived quiet, even though the numbers appear similar.
Common Wall Construction Types
A standard single-stud wall with one layer of 5/8-inch drywall on each side (STC 33 to 36) is typical residential construction. It allows speech to be heard clearly through the wall. Adding a second layer of drywall with acoustical damping compound raises performance to around STC 40 to 45, where speech becomes harder to discern but loud music remains audible.
Staggered stud construction places studs alternately on opposite edges of a wider plate, so the two drywall surfaces are not directly connected. This decoupling significantly reduces vibration transfer and typically achieves STC 45 to 55, depending on the number of drywall layers and the use of acoustic insulation in the cavity. Double-wall construction takes this further by building two entirely separate stud walls with an air gap between them, achieving STC 55 to 65 in well-executed assemblies.
Mass Loaded Vinyl (MLV) is a dense, flexible material that can be added to existing walls to increase mass without significantly increasing thickness. It typically adds 5 to 10 STC points when combined with existing construction. Resilient channels and sound isolation clips decouple the drywall from the studs mechanically, which is one of the most effective and cost-efficient ways to increase STC ratings in retrofits.
Flanking: The Weak Link
One of the most common reasons soundproofing projects underperform is flanking, the transmission of sound around a partition rather than directly through it. Sound travels through floors, ceilings, ductwork, electrical outlets, pipes, and any other shared structural element. A wall rated STC 55 in a laboratory can perform at STC 40 or lower in the field if flanking paths are not addressed.
Effective soundproofing requires treating the room as a system rather than focusing on a single partition. Sealing all penetrations, using resilient floor underlayments, and decoupling ceiling assemblies are all important complements to high-STC walls. The weakest element in any assembly, often a door or a single electrical outlet, governs the overall performance.
Setting a Target Noise Level
To use the target feature in this calculator, enter the maximum acceptable noise level on the quieter side of the wall. Common targets include 40 to 45 dB for sleeping areas, 45 to 50 dB for offices, and 50 to 55 dB for general living spaces. Libraries typically maintain 35 to 40 dB. Recording studios and home theaters often target 25 to 30 dB or lower.
If the calculator indicates your target is not met, the additional STC needed is shown. This can help you decide whether to upgrade the wall assembly, add additional layers of drywall, or consider supplementary treatments such as acoustic panels or door seals.
Limitations of This Calculator
This calculator provides a simplified estimate based on the airborne STC rating of a wall assembly. It does not account for low-frequency impact noise (such as footsteps or bass), which requires Impact Isolation Class (IIC) ratings for floors and ceilings. It also does not model flanking transmission, room acoustics, or the composite STC of assemblies that include doors or windows.
STC ratings are measured under controlled laboratory conditions. Field Sound Transmission Class (FSTC) values are typically 3 to 5 points lower than laboratory ratings. For critical applications such as recording studios, home theaters, or healthcare facilities, consulting an acoustic professional is recommended.
Frequently Asked Questions
What is STC rating and what does it mean?
STC (Sound Transmission Class) is a numerical rating of a wall or partition's ability to reduce airborne sound. The higher the number, the more sound is blocked. A standard drywall partition rates around STC 33, while high-performance double-wall assemblies can exceed STC 60. Each 10-point increase corresponds to roughly half the perceived loudness on the other side.
How is transmitted noise calculated?
The simplified formula is: Transmitted Noise (dB) = Source Noise (dB) minus STC Rating. For example, a 70 dB traffic noise source through an STC 40 wall would result in approximately 30 dB on the other side. This is an estimate; real-world results are affected by flanking paths, doors, and construction quality.
What STC rating do I need for a home studio?
A functional home studio typically requires STC 55 or higher to achieve meaningful isolation from everyday residential noise. Professional recording environments often target STC 65 to 70. Achieving these ratings requires double-wall or room-within-a-room construction with careful attention to flanking, doors, and HVAC penetrations.
Why is my wall not as quiet as the STC rating suggests?
STC ratings are measured in controlled laboratory conditions. In real buildings, sound travels through flanking paths including floors, ceilings, shared framing, ductwork, and electrical outlets, not just directly through the wall. These paths can reduce effective performance by 5 to 15 STC points or more. Sealing all penetrations and treating the room as a system is essential.
Does adding more drywall always improve soundproofing?
Adding mass (more drywall layers) does improve STC ratings, but with diminishing returns. The most effective approaches combine mass with decoupling (resilient channels, staggered or double studs) and absorption (acoustic insulation in the cavity). A decoupled wall with less total mass often outperforms a heavier but rigidly connected assembly.