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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Echo is measured as reverberation time: how long a sound takes to fade by 60 dB. Sabine's equation, RT60 = 0.049 × volume ÷ absorption, turns the gap between the time your room has now and the time you want into square feet of absorption, and that into a number of panels. A 12 × 15 × 8 ft office that rings for 0.8 s needs about 88 more sabins to reach 0.4 s: twelve 2 × 4 ft panels with an NRC of 0.95.
With these inputs:
| Result | Value |
|---|---|
| Acoustic panels needed | 12 panels |
| Absorption to add | 88.2 sabins |
| RT60 after the panels | 0.39 s |
| Room volume | 1,440 cu ft |
| Average absorption coefficient now | 0.111 |
What reverberation time should a room have?. Shorter is clearer for speech, and a room can be made too dead for music. The one widely cited US target is the classroom acoustics standard ANSI/ASA S12.60, which asks for 0.6 s or less in learning spaces up to 10,000 cu ft. Home offices and video-call rooms are usually aimed lower than that, and listening rooms are tuned by ear around the result you like. Set your own target and the calculator does the arithmetic. Sabine's equation assumes sound is spread evenly through the room. It is a planning tool for ordinary rooms; very small booths, rooms with one very absorbent surface and large halls need measurement or a more detailed model. Panels treat echo, not noise from next door. Absorption shortens the echo inside a room. It does very little to stop sound passing through a wall, which depends on mass, airtightness and decoupling. To keep noise in or out, see the soundproofing calculator for insulated cavities and wall assemblies. Spread panels over several walls and the ceiling rather than covering one wall, start at the first reflection points beside and above where you sit, and remember that soft furnishings, rugs and bookcases add absorption too: measure again after moving in.
RT60 = 0.049 × V ÷ A (V in cu ft, A in sabins) — Sabine; metric 0.161 × V ÷ A · Absorption now = 0.049 × V ÷ RT60 now; absorption needed = 0.049 × V ÷ RT60 target · Sabins per panel = panel face area × NRC · Panels = (absorption needed − absorption now) ÷ sabins per panel, rounded up
| Room | Volume | Sabins to add | Panels |
|---|---|---|---|
| Bedroom 12 × 12 × 8 ft | 1,152 cu ft | 70.6 | 10 |
| Home office 12 × 15 × 8 ft | 1,440 cu ft | 88.2 | 12 |
| Living room 16 × 20 × 9 ft | 2,880 cu ft | 176.4 | 24 |
| Basement studio 20 × 25 × 8 ft | 4,000 cu ft | 245 | 33 |
Computed with this calculator. Halving RT60 always means doubling the room's absorption.
With Sabine's equation: RT60 = 0.049 × room volume in cubic feet ÷ total absorption in sabins (0.161 × volume in m³ ÷ absorption in m² sabins). A sabin is one square foot of perfect absorption; a panel adds its face area times its absorption coefficient.
Work out the absorption the room needs for your target RT60 (0.049 × volume ÷ target), subtract what it has now (0.049 × volume ÷ current RT60), and divide by the sabins per panel (area × NRC). A 12 × 15 × 8 ft room going from 0.8 s to 0.4 s needs 88.2 sabins: twelve 2 × 4 ft panels at NRC 0.95.
The noise reduction coefficient: the average of a material's absorption coefficients at 250, 500, 1,000 and 2,000 Hz, measured to ASTM C423 and rounded to the nearest 0.05. 0 reflects everything; 1 absorbs everything in that range.
Use a free reverberation-time app on a phone: make a sharp sound such as a clap or balloon pop and the app times the decay. Take a few readings in different spots and use the average.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.