A comprehensive resource for safe and responsible laser use

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Beam Diameter and Irradiance Calculator

If you know the power and divergence of a visible, continuous wave laser, you can use the online calculator below to find out the beam diameter and irradiance at a given distance. The calculator also includes results for the Nominal Ocular Hazard Distance, beyond which the beam is considered to be safe for direct viewing.

We also have a full-featured Laser Hazard Distance Calculator, with the NOHD, ED50, and FAA visual interference distances.
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Beam Diameter and Irradiance Calculator
This calculator is valid only for lasers emitting visible (400-700 nanometers), continuous wave (CW) laser light, over long distances.
Enter the laser’s power in milliwatts.
If you know the power in watts, multiply the watts by 1000 to get milliwatts. For example, for a 1 watt laser, enter 1000; for a 1.5 watt laser, enter 1500; for a 40 watt laser enter 40000.
If you don’t know the beam divergence, use 1 milliradian for lasers under 500 milliwatts in power, and 1.5 milliradians for lasers 500 milliwatts and above.
Enter the distance from the laser output to the target or other desired distance. Just enter the distance number. Then use the drop-down list below to tell the calculator which distance unit you’re using: meters, kilometers, feet, miles, or nautical miles.
Results are below, in black. The beam diameter and NOHD results use the distance unit selected above. Results are continuously updated as you enter new information — you do not have to click a “=“ or “Calculate” button.
[dist] * [units]
Beam diameter result
A Gaussian laser beam is brightest in the center, and gradually falls off to the edges. The diameter listed here is the area where 63% of the beam power is contained, called the “1/e width.”

Specifically, “the distance between diametrically opposed points in that cross section of a beam where the power per unit area is 1/e (0.368) times that of the peak power per unit area.” This definition comes from the laser safety standard ANSI Z136.1.
NOTE: If all results are “.0000”, then the calculator does not work with your browser, which is probably Internet Explorer. Please use a different, up-to-date browser.
Irradiance result
Irradiance is the power of the laser, spread out over an area. Because laser beams diverge, the irradiance will be higher (more hazardous) closer to the laser, and will be lower (less hazardous) farther from the laser.
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.000 mW/cm²
[mw] / ( ( [beam-diameter] * [beam-diameter] ) * 7854 )
In watts per square meter: .000 W/m²
( [mw] / ( ( [beam-diameter] * [beam-diameter] ) * 7854 ) ) * 10
In watts per square centimeter: .000 W/cm². (Note: Because this online calculator only shows four decimal places, this may not be sufficient precision. If so, just divide the irradiance in mW/cm² by 1000 to get W/cm² with more decimal places.)
( [mw] / ( ( [beam-diameter] * [beam-diameter] ) * 7854 ) ) / 1000
Click for more details
Eye hazard result
The NOHD distance depends only on the power and divergence of the laser. It does not depend on the distance that you entered above.

Starting at the NOHD distance, laser light directly entering the eye is at the Maximum Permissible Exposure (MPE) and is generally considered safe. Specifically, at the NOHD there is “a negligible probability of damage” according to the laser safety standard ANSI Z136.1.

The farther one gets from the NOHD, the lower the irradiance, meaning that the light is even safer.
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( 32.8 / [mrad] ) * ( sqrt ( 0.5 * [mw] ) ) * 0.3048 / [units]
Compare with the beam diameter/irradiance distance you entered above. If the NOHD is greater than the beam diameter/irradiance distance, then there is an eye safety hazard (if a person’s eyes are allowed to view laser light at the beam diameter/irradiance distance).
For a full-featured Laser Hazard Distance Calculator, with the NOHD, ED50, and FAA visual interference distances, click here.
SAFETY NOTICE: The calculator above is intended for the educational, instructional and informational purposes of the user and is not to be considered a substitute for a knowledgeable and trained Laser Safety Officer (LSO) with the duties and responsibilities as defined in the ANSI Z136 standard. Consult with an LSO for safety-critical usage or special cases. While care has been taken to ensure accurate calculations, we are not responsible for errors. (If you do find errors please contact us with details.)

Additional laser hazard calculators

For a full-featured Laser Hazard Distance Calculator, with the NOHD, ED50, and FAA visual interference distances, click here.

We also have information about other calculators and dedicated programs. These can analyze complex situations involving multiple simultaneous colors, pulsed lasers, non-visible lasers, and/or atmospheric attenuation.

If you are a member of the International Laser Display Association, you can use ILDA’s free online Skyzan professional laser hazard calculator.