How to Calculate Room Acoustics: RT60 Reverberation Time and Acoustic Treatment
Learn how to calculate RT60 reverberation time using the Sabine and Eyring formulas, how absorption coefficients work, and how to determine how much acoustic treatment a room needs.
Related Calculators
What Is RT60?
RT60 (Reverberation Time) is the time it takes for a sound to decay by 60 dB (to one-millionth of its original energy) after the source stops. It's the primary metric for room acoustics and determines how "live" or "dead" a room sounds.
General RT60 guidelines: - Recording studio (vocal booth): 0.2–0.4 seconds - Recording control room: 0.3–0.5 seconds - Home listening room / HiFi: 0.3–0.5 seconds - Home theater: 0.3–0.5 seconds - Conference room: 0.5–0.8 seconds - Classroom: 0.6–0.8 seconds - Concert hall (classical): 1.5–2.5 seconds - Cathedral: 3–8 seconds
Sabine Formula
The most widely used RT60 formula:
RT60 = 0.161 × V / A (SI, metric) RT60 = 0.049 × V / A (imperial, feet)
Where: - V = room volume (m³ or ft³) - A = total absorption (sabins: m² or ft²) - 0.161 and 0.049 are Sabine constants
Total absorption: A = Σ(Si × αi) Where Si = surface area of material i, αi = absorption coefficient of material i
Absorption Coefficients (at 500 Hz)
Worked Example: 12 × 16 × 9 ft Bedroom Studio
Volume: 12 × 16 × 9 = 1,728 ft³
Surface areas and materials: | Surface | Area (ft²) | Material | α | Sabins | |---------|----------|---------|---|-------| | Floor | 192 | Carpet (heavy) | 0.45 | 86.4 | | Ceiling | 192 | Drywall | 0.05 | 9.6 | | Front wall | 108 | Drywall | 0.05 | 5.4 | | Back wall | 108 | Drywall | 0.05 | 5.4 | | Side walls (×2) | 288 | Drywall | 0.05 | 14.4 |
Total A = 86.4 + 9.6 + 5.4 + 5.4 + 14.4 = 121.2 sabins
RT60 = 0.049 × 1,728 / 121.2 = 84.7 / 121.2 = 0.70 seconds
This is slightly long for a recording room (target: 0.3–0.5 sec).
Treatment needed: Add 4-inch rockwool panels on walls and ceiling: Adding 100 ft² of panels (α = 0.90): A increases by 90 sabins → total A = 211 sabins New RT60 = 0.049 × 1,728 / 211 = 0.40 seconds ✓
Eyring Formula (Better for Highly Absorptive Rooms)
For rooms where average absorption > 0.3, the Eyring formula is more accurate:
RT60 = −0.049 × V / (S × ln(1 − ᾱ))
Where S = total surface area, ᾱ = average absorption coefficient (A/S), ln = natural log.
Sabine overestimates RT60 in very dead rooms; use Eyring for treated spaces.
Related Guides
Frequently Asked Questions
- What is a good RT60 for a home recording studio?
- A home recording control room should target RT60 of 0.3–0.5 seconds across most frequencies. Vocal booths need even shorter: 0.15–0.3 seconds. This short decay ensures recorded audio doesn't capture excessive room sound that conflicts with mixing. Too short (< 0.15 sec) can sound unnatural and fatiguing; too long (> 0.6 sec) causes comb filtering and muddy recording.
- How do I calculate how much acoustic treatment I need?
- 1. Calculate current RT60 using Sabine: RT60 = 0.049 × V / A (imperial). 2. Set target RT60. 3. Solve for needed absorption: A_needed = 0.049 × V / RT60_target. 4. A_to_add = A_needed − A_current. 5. Choose treatment panels: area needed = A_to_add / absorption coefficient of your panel. For 4-inch rockwool (α≈0.90), add that many sqft of panels.
- What is the Sabine formula and when is it used?
- The Sabine formula (RT60 = 0.161V/A in metric) is the fundamental equation for room reverberation time, derived by Wallace Clement Sabine in 1900. It's accurate for 'live' rooms where average absorption is below 0.3. For heavily treated rooms (studios, home theaters), the Eyring formula gives better accuracy because Sabine assumes sound fields that don't exist in absorptive spaces.
- Does room shape affect RT60 calculations?
- The Sabine formula ignores shape — it only uses volume and total absorption. Room shape mainly affects low-frequency modes (standing waves) which Sabine doesn't model. Rectangular rooms create strong axial modes that cause bass build-up at certain frequencies. Non-parallel walls and diffusion panels address modal issues that RT60 calculations alone won't capture.
Last updated 7/28/2026