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Laser Power Density: What, Why, and How to Calculate It

If you have a scalpel, you want to know how sharp it is.

If you have a hammer, you want to know how strong it is.

If you have a laser beam, you want to know its power density.

This can be argued, but I believe there is no single parameter that better characterizes how a laser will perform. Lasers are complex and you will likely want to measure many other aspects of it, but this one value will give you a lot of information.

If you are cutting sheet metal, the power density will determine how fast it can cut (and the quality of the cut as well). If you are performing laser surgery, the power density will need to be within a narrow range to ensure a successful operation. If you are testing the laser for safety purposes, the power density must be below a specific threshold where eye damage can occur.

Why is power density so important?

The secret to power density is it’s really two values combined into one. The power density is determined by the power of the laser divided by its cross-sectional area or beam size. Whether using the laser as a tool or ensuring its safety, you don’t just want to know the overall power, but how much power is hitting a particular area.

How to calculate power density

Ophir has a simple calculator for easily determining the power density of your laser.


  • Enter the diameter of your laser beam (in mm)
  • Enter its power level
  • Click “Calculate,”

… and you will get your laser power density, in W/cm2:

For pulsed laser beams, you can enter the power or energy level to get the power or energy density of the laser. If you include you beam repetition rate, the calculator will automatically give you both values.

Finally, be sure to select the correct parameters for your laser mode (profile) and beam shape, as these affect the results significantly.

Click here to use the laser power density calculator, or click here for all our laser calculators.



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