How are decibels calculated?

Power and intensity ratios use 10 times the base-10 logarithm of the ratio. Pressure and amplitude ratios use 20 times the base-10 logarithm.

Why can decibel levels not be added normally?

Decibels are logarithmic values. Each level must be converted to linear energy, combined, and converted back to decibels.

What happens when two 60 dB sources are combined?

Two independent 60 dB sound sources produce a combined level of approximately 63 dB.

How much does sound decrease when distance doubles?

Under ideal free-field conditions, doubling the distance from a point sound source reduces the sound pressure level by approximately 6 dB.

Can this calculator replace a sound level meter?

No. The calculator processes entered measurements, while a calibrated sound level meter is required to measure real environmental noise.

Acoustic Measurement Tool

Decibel Calculator

Calculate sound pressure levels, sound intensity, power ratios, combined noise levels, and expected decibel changes over distance.

Calculate a Decibel Value

Select a calculation type and enter your measurements.

Sound intensity (I)

Enter intensity in watts per square metre.

Reference intensity (I₀)

Standard air reference: 1 × 10⁻¹² W/m².

Sound intensity formula L = 10 × log₁₀(I ÷ I₀)

Sound pressure (p)

Enter RMS sound pressure in pascals.

Reference pressure (p₀)

Standard air reference: 20 µPa.

Sound pressure level formula SPL = 20 × log₁₀(p ÷ p₀)

Output power (P₂)

Reference power (P₁)

Power ratio formula dB = 10 × log₁₀(P₂ ÷ P₁)

Output amplitude (A₂)

Reference amplitude (A₁)

Amplitude ratio formula dB = 20 × log₁₀(A₂ ÷ A₁)

Individual sound levels (dB)

Decibel levels cannot be added using ordinary arithmetic. The calculator combines their logarithmic sound energies.

Combined level formula Ltotal = 10 × log₁₀(Σ 10^Li/10)

Initial sound level

Measured sound level in decibels.

Initial distance

New distance

Distance unit

Free-field distance formula L₂ = L₁ − 20 × log₁₀(r₂ ÷ r₁)

6 Calculation Modes Pressure, intensity, ratios, distance, and more.

Instant Results Calculations update directly in your browser.

Private Processing Your measurement values are not uploaded.

Mobile Friendly Use the calculator on desktop, tablet, or mobile.

How It Works

Calculate Decibels in Three Simple Steps

Choose the formula that matches your measurement and let the calculator perform the logarithmic conversion.

Select a Calculation

Choose sound intensity, pressure, power ratio, amplitude ratio, combined levels, or distance change.

Enter Your Values

Add the measured value, reference value, sound levels, or distances required by the selected formula.

Review the Result

Receive the decibel result with its calculation type, ratio information, and general sound category.

What Is a Decibel Calculator?

A decibel calculator converts a ratio between two physical quantities into decibels. Decibels are commonly used to describe sound pressure, sound intensity, electrical gain, signal loss, and power relationships.

The decibel scale is logarithmic rather than linear. A change of 10 dB represents a tenfold change in power or intensity. For amplitude quantities such as pressure or voltage, a change of approximately 20 dB represents a tenfold ratio.

Why Decibels Use Logarithms

Sound intensity can vary across an extremely large numerical range. A logarithmic scale compresses those values into numbers that are easier to compare and communicate.

A 3 dB increase is approximately twice the sound power.
A 10 dB increase represents ten times the intensity.
Two equal sound sources increase the total by about 3 dB.
Doubling distance often reduces free-field sound by about 6 dB.

Sound Pressure and Sound Intensity

Sound pressure level uses a factor of 20 because pressure is an amplitude quantity. Sound intensity and acoustic power use a factor of 10 because they are power quantities.

Typical Sound Level Examples

Sound source	Approximate level
Breathing	10 dB
Quiet library	30–40 dB
Normal conversation	55–65 dB
Vacuum cleaner	70–80 dB
Motorcycle	90–100 dB
Live concert	100–115 dB
Jet aircraft nearby	120–140 dB

Sound examples are approximate. Actual exposure depends on distance, environment, equipment, duration, and the accuracy of the measuring device.

Frequently Asked Questions

Decibel Calculator FAQs

Learn how decibel measurements, sound ratios, and combined noise levels are calculated.

Power and intensity ratios use 10 × log₁₀(value ÷ reference). Pressure, voltage, and other amplitude ratios use 20 × log₁₀(value ÷ reference).

Decibels represent logarithmic ratios. To combine noise sources, each level must first be converted to linear energy, added, and then converted back into decibels.

Two independent sources measuring 60 dB each produce a combined level of approximately 63 dB, not 120 dB.

Under ideal free-field conditions, doubling the distance from a point source reduces the sound pressure level by approximately 6 dB.

The commonly used reference sound pressure in air is 20 micropascals, equal to 0.00002 pascals.

No. This calculator processes measurements you enter. A calibrated sound level meter is needed to measure real environmental noise accurately.