Mass Law Transmission Loss Calculator
The mass law predicts how much airborne sound a single, limp wall or panel blocks. Transmission loss climbs by about 6 decibels each time you double the panel's surface mass or the frequency, so heavier barriers and higher pitches are blocked more effectively. This calculator applies the field-incidence mass law to estimate transmission loss in decibels from a panel's surface mass and a frequency. Surface mass density is a user input because it depends on your material and thickness.
Mass law formula
transmission loss = 20 * log10(surface mass * frequency) - 47
one octave up = 20 * log10(surface mass * 2 * frequency) - 47
mass doubled = 20 * log10(2 * surface mass * frequency) - 47
each doubling of mass or frequency adds about 6 dB
This field-incidence form uses surface mass in kilograms per square metre and frequency in hertz. The 47 decibel constant accounts for random incidence; a normal-incidence form uses about 42.
Sound isolation facts
- Doubling panel mass adds roughly 6 decibels of transmission loss.
- Each octave higher in frequency adds about 6 decibels.
- The mass law ignores stiffness, so real panels dip at the coincidence frequency.
- Two separated leaves can far exceed the mass law of a single panel.
- Low frequencies are the hardest to block, needing the most mass.
Transmission loss: frequently asked questions
What is the mass law in acoustics?
The mass law describes how a single, limp partition blocks airborne sound. Transmission loss rises with both the surface mass of the panel and the frequency: roughly 6 decibels per doubling of either mass or frequency. Heavier walls and higher pitches are blocked more.
What is the mass law formula?
A common field-incidence form is transmission loss = 20 times log base 10 of (surface mass times frequency) minus 47 decibels, with surface mass in kilograms per square metre and frequency in hertz. The 47 constant is for random (field) incidence.
Why 6 dB per octave and per doubling of mass?
Because the loss depends on the logarithm of mass times frequency multiplied by 20, doubling either term adds 20 times log base 10 of 2, which is about 6 decibels. So each octave up, or each doubling of weight, adds roughly 6 decibels of isolation.
When does the mass law not apply?
The mass law ignores stiffness, damping and resonances. Real panels show a coincidence dip at high frequencies and resonance effects at low frequencies, so measured isolation can be lower than the mass law near those regions. Use it as a single-panel estimate.
What is surface mass density?
It is the mass per unit area of the panel, in kilograms per square metre, equal to material density times thickness. It is a user input because it depends on your specific material and thickness, which you can look up or measure.
Official sources
- International Organization for Standardization: ISO 717 rating of sound insulation.
- Acoustical Society of America: building acoustics references.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.