What is the inverse square law for radiation?

The inverse square law states that radiation dose rate is proportional to the inverse of the distance squared. Doubling the distance reduces dose rate to one quarter; tripling the distance reduces it to one ninth.

What units can I use?

Distance can be entered in meters, centimeters, or feet. Dose rate can be entered in mSv/h, μSv/h, mR/h, or R/h. The output uses the same unit you select for dose rate.

Does this account for shielding or scatter?

No. This calculator assumes a point source in open air with no shielding or scattering material. Real-world scenarios with walls, shielding, or large sources require additional factors.

Why does dose rate change so fast with distance?

Because the inverse square law is quadratic. A small increase in distance produces a large drop in dose rate, which is why distance is the most effective and cheapest radiation protection measure.

Can I use this for light or sound intensity too?

Yes. The inverse square law applies to any point source radiating uniformly in all directions: radiation, light, gravity, and sound intensity all obey the same relationship.

Radiation Distance Dose Calculator

Enter a known dose rate and reference distance to find the dose rate at any new distance using the inverse square law.

Known Reference Point

Dose Rate at Reference Distance

Reference Distance

New Distance

Exposure Time (optional — for total dose)

Results

Enter values and press Calculate.

Distance vs. Dose Rate — Quick Reference

Relative to reference point (×1). Values update after each calculation.

Multiplier	Distance	Dose Rate	% of Reference
Calculate first to populate table.

Summary

The Radiation Distance Dose Calculator applies the inverse square law (D2 = D1 × (r1/r2)²) to compute the dose rate at any distance from a point radiation source. Enter a known dose rate at a reference distance, then provide the new distance to instantly see how dose rate changes. An optional exposure time field converts dose rate to total accumulated dose for safety planning.

How it works

Enter the known dose rate at a reference distance (e.g. 2 mSv/h at 1 meter).
Enter the new distance where you want to find the dose rate.
The tool applies the inverse square law: D2 = D1 × (r1 / r2)².
Read the calculated dose rate at the new distance.
Use the exposure time field to get total accumulated dose.

Use cases

Determine safe working distances around radiation sources.
Estimate dose rates at different positions in a radiation facility.
Plan shielding layouts by understanding distance attenuation.
Verify compliance with occupational dose limits during source handling.
Calculate dose for patient or worker positioned at a specific distance.
Train radiation safety officers with live inverse-square-law examples.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu