Calculator inputs
Use the fields below to estimate STC for common wall and partition assemblies.
Example data
These examples show how changes affect the estimate. Use them as a starting point for your own scenarios.
| Scenario | Preset | Layers A/B | Channels | Sealing | Openings | Estimated STC |
|---|---|---|---|---|---|---|
| Basic office partition | Wood studs 2x4 + insulation | 1 / 1 | None | Careful | No | ~38 |
| Improved meeting room wall | Wood studs 2x4 + insulation | 2 / 2 | One side | Excellent | No | ~52 |
| Block wall with door | Concrete block 200mm (grouted) | — | — | Careful | Solid core | ~42 |
| High isolation studio partition | Double stud wall | 2 / 2 | One side | Excellent | No | ~63 |
Numbers are approximate and depend on workmanship, detailing, and flanking.
Formula used
This estimator uses a practical, assembly-based method. It starts from a baseline STC for a typical partition type, then applies gains and penalties for upgrades and real-world weak points.
- Extra board layers: about +3 per added layer.
- Heavier board: about +2 for thicker boards.
- Resilient channels: about +5 (one side) to +8 (both).
- Cavity insulation in stud walls: about +3 to +4.
- Careful sealing: about +2 to +3 for airtightness.
- Penetrations and unsealed services: roughly −1 to −5.
- Windows: roughly −0.5 per 1% window area.
- Doors: roughly −3 to −10 depending on door type.
- Flanking: roughly −2 to −5 if not controlled.
How to use this calculator
- Select the closest Assembly preset for your wall.
- Adjust layers, thickness, insulation, and channels to match your design.
- Enter openings and penetrations; these often reduce actual isolation.
- Set sealing and flanking risk based on detailing and site conditions.
- Click Estimate STC to view the result and breakdown.
- Use Download CSV or Download PDF for records.
STC estimating guide for construction planning
Sound Transmission Class (STC) is a single-number rating used to compare how well a wall or partition reduces airborne sound between adjacent spaces. In practice, STC is influenced by both the assembly (mass, stiffness, and decoupling) and the details (air sealing, penetrations, and flanking paths). This calculator is designed for early design and budgeting stages, when you need a fast comparison of multiple wall options before committing to a tested system.
The estimate begins with a baseline STC for a typical construction type, then adjusts the result using common performance drivers. Adding board layers increases surface mass and can improve mid-to-high frequencies. Resilient channels reduce structural coupling and often provide a noticeable jump. Cavity insulation in stud walls reduces resonance and improves transmission loss through the cavity. Finally, airtightness matters: small gaps at perimeters, electrical boxes, or service penetrations can reduce the apparent rating even when the core wall is strong.
Openings usually control the outcome. A door, glazing, or repeated penetrations can pull the effective performance down to the weakest element. For example, an improved meeting room wall using a wood-stud insulated preset with 2 / 2 layers, one-side channels, and excellent sealing may estimate near STC 52. If you add a standard solid core door without full perimeter seals, the effective estimate can drop into the low-to-mid 40s. That change can be the difference between “speech is a murmur” and “speech is audible.”
Use the example table above as reference data. A basic office partition often lands around STC 38, suitable for general separation but not confidential meetings. A double-stud wall with extra layers and good sealing can exceed STC 60 and is better for studios or sensitive rooms. For masonry or concrete, the baseline is higher due to mass, but detailing still matters because flanking through slabs, ceilings, or ducts can reduce real-world performance.
When comparing options, document the exact inputs you assumed, including board count, stud depth, insulation type, and any openings. Keep a consistent basis across alternatives so the relative differences remain meaningful. Exporting the CSV or PDF helps teams review selections and track revisions during design.
Treat this output as a screening estimate. When the target STC is contractual or regulatory, select a lab-tested assembly and verify the full construction details (seals, back-to-back boxes, ceilings, and services). The best results come from combining a strong wall design with careful workmanship and flanking control.
FAQs
1) What does an STC number actually tell me?
STC compares airborne sound isolation of partitions. Higher numbers mean better speech privacy. It does not directly rate impact noise, vibration, or low-frequency bass performance.
2) Why can a good wall still perform poorly on site?
Air leaks, gaps, unsealed penetrations, and flanking through ceilings, slabs, or ducts can bypass the wall. Real performance depends heavily on detailing and workmanship.
3) Do resilient channels always improve the result?
They usually help by reducing vibration coupling, but improper installation, short-circuiting, or heavy fixtures can reduce the benefit. Follow spacing, fastener, and backing guidance.
4) Is insulation useful if the wall already has multiple layers?
Yes for stud walls. Insulation dampens cavity resonance and improves mid-frequency loss, even when mass is increased. It is less relevant for solid concrete or fully grouted masonry.
5) How should I treat doors and glazing in STC planning?
Openings often become the weak link. Use sealed acoustic door sets and appropriate glazing. Even a strong wall can be limited by an unsealed door or large glazed percentage.
6) What STC ranges suit common room types?
Around 35–40 fits general offices, 45–50 supports meeting rooms, and 55+ is typical for high privacy or studios. Targets vary with background noise and occupant expectations.
7) Can this estimate replace a tested assembly report?
No. Use it for early comparison and budgeting. For final design, select assemblies with verified laboratory ratings and coordinate details for sealing, flanking, and services.