STC Calculator | FreeAcoustics.tools

What is STC?

Sound Transmission Class (STC) measures how well a wall, floor, or ceiling blocks airborne sound like voices, TV, and music. It's the primary rating for speech privacy between rooms. Unlike IIC which measures footsteps, STC focuses on sounds that travel through the air.

Higher STC = better blocking. STC 25 means loud speech is clearly understood; STC 50 means loud speech is inaudible; STC 60+ provides studio-grade isolation where most sounds are completely blocked.

Transmission Loss by Frequency (dB) ?

Note: Enter TL values from lab test per ASTM E90. STC is computed per ASTM E413 curve-fitting method.

Common Wall Assemblies

Note: STC ratings match published industry data. TL curves are representative estimates based on typical wall behavior. For exact values, use Manual Entry with data from an ASTM E90 test report.

Mass Law Estimation ?

Surface Mass

Units

Mass Law: TL ≈ 20 log₁₀(m × f) − 47 dB (for single leaf panels at normal incidence). Add 6 dB for each doubling of mass. This is a theoretical estimate; real assemblies may vary ±5 STC due to coincidence effects and flanking paths.

Sound Transmission Class ?

Enter TL data

Code Requirements

IBC 2021 (dwelling units) STC 50

HUD Min. Property Standards STC 45

Hotel/Motel (privacy) STC 50

Hospital patient rooms STC 50

Recording studio STC 60+

What You'll Hear

Enter STC data to see expected sound isolation performance.

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