Understanding your result
The headline is the laboratory STC range published for the assembly you chose, and the line under it says whether that range meets your target, may meet it, or does not. “May meet” means the target is inside the range: the wall can reach it in a lab, but a real house, with its outlets and gaps, may not. The bars show every assembly in the list on the same scale, so you can see what each step up buys.
The tiles and the table list what the assembly takes for your wall: sheets on each side, studs (two rows for staggered and double walls), resilient channel where the assembly uses it, mineral wool packs, and the acoustic sealant at the perimeter of both sides. The materials are the assembly’s, and the rating belongs to the assembly as tested; a substitution changes both.
The notes say where the numbers came from and what costs points in the field. To count one material in detail, use the Green Glue calculator for damping compound, the resilient channel calculator for the channel, and the insulation calculator for the batts. Ceilings are a separate problem with their own clips, in the isolation clip calculator.
How we calculate this
The STC ranges come from the Gypsum Association’s Fire Resistance and Sound Control Design Manual (GA-600) where we could cite a file number, and from published summaries of laboratory tests (ASTM E90) for the common single-stud builds. They are collected with their sources on the sound and fire assemblies page. The calculator does not interpolate: if you add a layer to an assembly that has not been tested that way, the honest answer is the nearest tested assembly, not a new number.
Insulation is counted at Rockwool’s published pack coverage for 3 in mineral wool; the stud count follows the site’s shared stud layout.
The assumptions behind the numbers
| Assembly | Lab STC | Source |
|---|---|---|
| Single 2 × 4 studs, one layer each side, no insulation | 33–35 | GA-600 single-stud listings; published summaries |
| Single studs, one layer each side, insulation | 34–39 | GA-600 listings; published summaries |
| Single studs, insulation, two layers on one side | 41–44 | Published summaries of lab tests |
| Single studs, insulation, resilient channel and two layers on one side | 48–52 | Published summaries of lab tests |
| Staggered studs on a 2 × 6 plate, one layer each side, insulation | 46–49 | Published summaries (about STC 48) |
| Staggered studs, two layers of type X each side (2-hour) | 50–54 | GA-600 file WP 3910 |
| Double 2 × 4 studs, 1 in apart, two layers each side (2-hour) | 55–59 | GA-600 file WP 3810 |
| Field results | 3 to 5 points below lab | Published field-test comparisons |
Assumptions last reviewed October 8, 2026.
The calculator covers walls only. It does not rate ceilings and floors, which also have an impact rating (IIC); it does not rate steel-stud walls, which have their own listings; and it does not model doors, windows or ducts in the wall, which are usually the weak point. Why mass, damping and decoupling work, and which is cheapest per point, is in the soundproofing basics guide; the ceiling version is in the ceilings guide.
Two worked examples
A 14 × 8 ft bedroom wall: insulated single studs, target STC 45
- Assembly: single 2 × 4 studs, one layer each side, insulation: STC 34–39
- Does not meet STC 45; the lightest assembly in the list that does is two layers on one side (STC 41–44 is still short), so the calculator points to resilient channel (48–52)
- Materials as chosen: 4 sheets each side, 13 studs, 2 packs of mineral wool, 88 ft of perimeter to seal
Insulating an ordinary wall is worth doing but will not reach 45. Adding channel and a second layer on one side is the smallest change that does.
A 16 × 9 ft media room wall: staggered studs, two layers each side, target STC 50
- Assembly: GA-600 WP 3910 type, STC 50–54, also a two-hour wall when built with type X
- Meets STC 50 in the lab; build carefully, because the field takes 3 to 5 points
- Materials: 10 sheets each side, 30 studs on 2 × 6 plates, 3 packs of mineral wool, 100 ft of sealant
A staggered wall is only 2 in thicker than a normal one and needs no channel. The back-to-back outlet rule matters most here: offset the boxes by a stud bay.
Where to find your inputs
Assembly. The one you plan to build, or the closest to what is already there plus what you will add.
Wall size. Length and height of the wall between the rooms.
Target. STC 45 for a quieter bedroom or office, 50 for privacy and the multifamily code level, 55 for a media room or a bedroom next to one.
Sheet size. The board size you will hang; it changes the sheet count, not the rating.
Common mistakes
- Adding parts to a rating. Ratings are for tested assemblies. Two layers plus channel plus Green Glue is not the sum of their marketing numbers.
- Back-to-back outlets. They make a hole through the wall. Offset boxes by at least one stud bay and seal them.
- Unsealed perimeter. A gap at the floor or ceiling leaks more than the wall stops. Acoustic sealant on both sides.
- Shorting the channel. One board screw into a stud and the channel is bypassed.
- Ignoring the door. A hollow-core door is about STC 20. A good wall around it is wasted without a solid, gasketed door.
- Expecting bass to stop. STC is weighted to speech; low-frequency sound from a subwoofer needs more mass and decoupling than the rating suggests.
Questions people ask
- What is the STC of a normal interior wall?
- A single 2 × 4 stud wall with one layer of drywall on each side and nothing in the cavity tests at about STC 33 to 35. With insulation in the cavity it is about 34 to 39. Normal speech is clearly understood through STC 35 and is only faintly heard through STC 50.
- How do I get an STC 50 wall?
- The usual routes are decoupling and mass: resilient channel with two layers of board on one side of an insulated single-stud wall (about STC 48 to 52 in lab tests), or a staggered-stud wall with two layers each side (GA-600 file WP 3910, STC 50 to 54). Field results run 3 to 5 points below the lab.
- What STC does a double stud wall get?
- A double row of 2 × 4 studs with a 1 in gap, two layers of type X each side and insulation is listed in GA-600 file WP 3810 at STC 55 to 59, and it is also a two-hour fire-rated wall. It is the most effective of the common builds and takes the most floor space.
- Does insulation make a wall soundproof?
- It helps, by a few points: insulation in the cavity of a single-stud wall raises it from about STC 33 to 35 to about 36 to 39 in published tests. The large improvements come from adding mass (more board), damping between layers, and decoupling the two sides.
- Why is my wall quieter in the lab than in my house?
- Lab tests measure only the wall. In a house, sound also travels around it: through outlets back to back, gaps at the floor and ceiling, ducts, doors and the floor structure. Field ratings (ASTC) typically come in 3 to 5 points lower, and a single unsealed gap can cost 10 points or more.
- What STC rating do I need between rooms?
- The International Building Code requires STC 50 (45 field-tested) between dwelling units in multifamily buildings. Inside a house there is no requirement; STC 45 to 50 makes a bedroom or office noticeably private, and STC 55 or more is home-theatre territory.