db to distance calculator

Estimate how far you need to be from a sound source to reach a target sound level using free-field sound propagation.

Formula: L₂ = L₁ - 20 log₁₀(d₂/d₁)
Rearranged for distance: d₂ = d₁ × 10^{((L₁ - L₂)/20)}

Sound level at known distance (dB)

Known distance from source

Unit of known distance

Target sound level (dB)

If target dB is higher than reference dB, the result will be a closer distance.

What This dB to Distance Calculator Does

This calculator converts a sound level difference in decibels (dB) into an estimated distance from a source. It is useful in audio setup, noise control planning, workplace safety checks, live event design, and general acoustics work.

You provide:

A measured or known sound level at a known distance.
Your target sound level.

The calculator returns the distance where that target level is expected, assuming open-air conditions and no strong reflections.

How the Math Works

Inverse Distance Rule for Sound Pressure

In a free field, sound pressure level from a point source drops by roughly 6 dB every time distance doubles. That behavior comes from:

Level change (dB) = 20 × log₁₀(distance ratio)

Rearranging gives the direct distance equation used above. This makes it easy to solve for unknown distance when both dB levels are known.

Quick Rule of Thumb

Double the distance → about −6 dB
Half the distance → about +6 dB
10× farther → about −20 dB

Step-by-Step Usage

Enter the sound level measured at a known point (for example, 90 dB at 1 meter).
Enter that known distance and its unit (meters or feet).
Enter the target level you want to reach (for example, 70 dB).
Click Calculate Distance to see the predicted distance in meters and feet.

Worked Example

Suppose a speaker reads 96 dB at 1 m. You want to know how far away it will be about 78 dB.

Difference = 96 − 78 = 18 dB
Distance factor = 10^(18/20) ≈ 7.94
Distance ≈ 1 m × 7.94 = 7.94 m

So you would expect around 7.9 meters (about 26 feet) in free-field conditions.

Important Assumptions and Limits

This calculator is a practical estimate, not a full acoustic simulation. Accuracy depends on conditions:

Point-source behavior: Real sources can be directional, not perfectly point-like.
No room effects: Reflections in rooms can increase levels versus open-space predictions.
No air absorption model: Long distance and high frequencies can lose extra energy.
No obstacles: Walls, barriers, and crowds affect propagation.

For critical design work (compliance, permitting, detailed venue planning), use professional measurement and modeling tools.

Common Use Cases

Setting safe listener distances near speakers.
Planning equipment placement for events and rehearsals.
Estimating noise exposure around machinery.
Checking approximate impact zones for alarms or public-address systems.

FAQ

Is dB linear with distance?

No. dB is logarithmic, so distance changes create non-linear dB changes.

Why use 20 and not 10 in the formula?

We are relating sound pressure level to distance. Pressure ratios use 20·log10, while power ratios use 10·log10.

Can I use this indoors?

Yes for rough estimates, but indoor reflections can make actual levels higher than free-field predictions.