STC – Sound Transmission Class

STC is a rating that measures how well an entire window system-including the glass, frame, and seals-reduces airborne sound transmission from the outside into a building. It is expressed in decibels (dB) and calculated based on American testing standards, including ASTM E90 (laboratory measurement of airborne sound transmission loss) and ASTM E413 (classification method for rating sound insulation).

The higher the STC value:

• The better the window is at blocking outside noise
• The less you hear things like street traffic, conversations, or airplane noise indoors

Example STC ratings for windows:

• STC 25-30: standard single-pane windows; provide basic sound insulation but allow most street noise through
• STC 30-35: typical double-pane (insulated) windows with average acoustic performance
• STC 35-45: specialized windows, often with thicker or laminated glass; significantly improve acoustic comfort
• STC 45+: high-performance soundproof windows; commonly used near airports, in hotels, or buildings requiring strong noise control