Physics

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Distance Attenuation Calculator.

Calculate inverse-square geometric spreading from a measured reference distance and intensity.

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Set your values

Results update as you type.

02 / ANSWER

Reference distance

Reference intensity

Target distance

Target intensity

0.000000relative

Intensity ratio

0.000000×

Attenuation

0.000000dB

Results update automatically as you type.

Use Cases

Estimate sound level at a distance

Given a measured sound intensity at a known distance, predict the intensity at a farther or closer location in an open environment.

Example: If a speaker produces 100 units at 1 m, what is the intensity at 10 m? (Answer: 1 unit)

Plan lighting for a room

Determine how light intensity falls off from a lamp to help position fixtures for even illumination.

Example: A lamp gives 500 lux at 2 m; find lux at 4 m.

Frequently Asked Questions

What is the inverse-square law in this calculator?: The inverse-square law states that intensity is inversely proportional to the square of the distance from the source. This calculator uses your reference distance and intensity to compute the intensity at a target distance, assuming free-field spreading.
What units should I use for reference and target distance?: Both distances must be in meters (m). The reference intensity can be in any relative unit (e.g., watts per square meter, decibels, or arbitrary units) because the result is proportional to that input.
Can I use this calculator for sound or light?: Yes, the inverse-square law applies to any point source emitting energy in three dimensions, such as sound waves in free air or light from a small bulb. However, it assumes no absorption, reflection, or obstacles.

Tips & Common Mistakes

Tips

Ensure both distances are in meters; convert if necessary (1 m = 3.28 ft).
Use consistent relative units for intensity; the result will be in the same units.
This calculator assumes free-field conditions with no reflections or absorption; real environments may differ.
For sound, remember that a 6 dB decrease corresponds to doubling distance in free space.

Common Mistakes to Avoid

Forgetting to square the distance ratio when applying the inverse-square law.
Using different units for reference and target distance (e.g., meters and feet) without conversion.
Assuming the law applies in enclosed spaces with reflections, where intensity may not follow the inverse-square rule.

Last updated: August 13, 2026

Use Cases

Estimate sound level at a distance

Given a measured sound intensity at a known distance, predict the intensity at a farther or closer location in an open environment.

Example: If a speaker produces 100 units at 1 m, what is the intensity at 10 m? (Answer: 1 unit)

Plan lighting for a room

Determine how light intensity falls off from a lamp to help position fixtures for even illumination.

Example: A lamp gives 500 lux at 2 m; find lux at 4 m.

Frequently Asked Questions

What is the inverse-square law in this calculator?

The inverse-square law states that intensity is inversely proportional to the square of the distance from the source. This calculator uses your reference distance and intensity to compute the intensity at a target distance, assuming free-field spreading.

What units should I use for reference and target distance?

Both distances must be in meters (m). The reference intensity can be in any relative unit (e.g., watts per square meter, decibels, or arbitrary units) because the result is proportional to that input.

Can I use this calculator for sound or light?

Yes, the inverse-square law applies to any point source emitting energy in three dimensions, such as sound waves in free air or light from a small bulb. However, it assumes no absorption, reflection, or obstacles.

Tips & Common Mistakes

Tips

Ensure both distances are in meters; convert if necessary (1 m = 3.28 ft).
Use consistent relative units for intensity; the result will be in the same units.
This calculator assumes free-field conditions with no reflections or absorption; real environments may differ.
For sound, remember that a 6 dB decrease corresponds to doubling distance in free space.

Common Mistakes to Avoid

Forgetting to square the distance ratio when applying the inverse-square law.
Using different units for reference and target distance (e.g., meters and feet) without conversion.
Assuming the law applies in enclosed spaces with reflections, where intensity may not follow the inverse-square rule.

Use Cases

Estimate sound level at a distance

Given a measured sound intensity at a known distance, predict the intensity at a farther or closer location in an open environment.

Example: If a speaker produces 100 units at 1 m, what is the intensity at 10 m? (Answer: 1 unit)

Plan lighting for a room

Determine how light intensity falls off from a lamp to help position fixtures for even illumination.

Example: A lamp gives 500 lux at 2 m; find lux at 4 m.

Frequently Asked Questions

What is the inverse-square law in this calculator?

What units should I use for reference and target distance?

Can I use this calculator for sound or light?

Tips & Common Mistakes

Tips

Ensure both distances are in meters; convert if necessary (1 m = 3.28 ft).
Use consistent relative units for intensity; the result will be in the same units.
This calculator assumes free-field conditions with no reflections or absorption; real environments may differ.
For sound, remember that a 6 dB decrease corresponds to doubling distance in free space.

Common Mistakes to Avoid

Forgetting to square the distance ratio when applying the inverse-square law.
Using different units for reference and target distance (e.g., meters and feet) without conversion.
Assuming the law applies in enclosed spaces with reflections, where intensity may not follow the inverse-square rule.