STC Ratings and What They Mean for Your Home

Nov 25, 2022

When it comes to selecting new windows for your home, there are a number of factors to consider, from the window color and operating style to energy efficiency. One thing many homeowners forget to look for is the sound rating, which measures the amount of sound a window will let into their home – yet noise reduction windows can increase your home’s overall comfort and tranquility.                                   

To determine how much sound is transmitted through a window, manufacturers conduct testing to calculate ratings for two primary ratings: Sound Transmission Class (STC) and Outdoor/Indoor Transmission Class (OITC). 


What Is an STC Rating?

Sound Transmission Class (STC), also known as the Sound Transmission Coefficient, is the oldest and most widely recognized sound rating system in the window and door industry. STC ratings are measured as a difference in decibel levels, where a higher rating indicates more complete sound absorption and sound deadening performance. STC ratings of materials were originally developed to measure the sound transmission between interior walls.

The STC test to determine the rating involves settling up a sound transmitter inside the window being tested and a receiver outside of it. Sounds are played from inside the window at predetermined frequencies ranging from 125 Hz to 4000 Hz to account for noises often heard inside the home. The sound is picked up by the receiver outside the window, which measures how much sound was transferred through the window. 

The difference between the sound level inside the window and the sound level outside the window, measured in decibels, is the STC rating. For example, if the transmitter played a sound at 60 decibels and the receiver picked up 30 decibels, the STC rating would be 30. The same process is used to determine STC ratings for doors.


What Is an OITC Rating?

Outdoor/Indoor Transmission Class (OITC) is a newer rating system developed specifically for measuring sound transmission of low- and mid-frequency noises through exterior walls. Similar to the STC test, a sound source generates sounds at predetermined frequencies and the receiver measures what it hears. These frequencies have a wider range – 80 Hz to 4000 Hz – in order to account for lower-level noises often heard outdoors, such as traffic and airplanes.


What Affects the STC Ratings of Windows and Doors?

As you shop for new windows or patio doors, you’re bound to come across plenty of features that help improve energy efficiency. The factors that can influence the STC rating of windows and doors include:



Any of these factors, alone or in combination, can have an impact on the STC rating and performance of your window or door. A four-point STC improvement can cause a clearly perceptible change in your home’s acoustics, while a 10-point improvement can reduce sound by 50 percent.


What Is a Good STC Rating?

An excellent rating is an STC of 60 or higher. At this rating, you may be able to hear very loud sounds faintly, but most sounds you won’t hear at all. On the other hand, a typical window has an STC rating of 25 to 30. At this rating, you would be able to comfortably hear a conversation going on outside. 


STC Rating Chart

To understand STC ratings, it’s easiest to summarize them in a chart as we’ve done below.

STC Rating Chart, MI Windows and Doors

Maintain Your Home’s Serenity with Noise Reduction Windows

Sound reduction is an important piece of overall window and door performance, especially if you live in a noisy area. Selecting a product with an above-average STC rating will not only enhance the value of your home, but can also provide a more comfortable setting for you and your family. Plus, some of the same features that help glass block out sound also improve your home’s energy efficiency, making sound-rated windows an even better value.

If you’re ready to get a good night’s sleep, contact a Certified MI Dealer in your area and ask about our STC ratings. Our windows and patio doors have a variety of energy-efficient and sound-reducing features, so you can find the perfect match for your product.


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