Physics

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Laser Spot Size Calculator.

Calculate the diffraction-limited Airy-disk diameter for a circular aperture with explicit wavelength and focal geometry.

On-device calculationNo signup
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Set your values

Results update as you type.

Airy angular radius: 0.0000771 rad

Airy angular radius

0.00000000rad
Airy diameter: 0.00000771 m

Airy diameter

0.00000000m

Results update automatically as you type.

The model is the circular-aperture Airy pattern (2.44 λf/D), not a Gaussian-beam, lens-aberration, alignment, or power-density estimate.

Use Cases

Optical System Design

Determine the minimum achievable spot size for focusing a laser beam with a lens or mirror, helping to select appropriate optics for applications like laser cutting or microscopy.

Example: A 532 nm laser with a 10 mm focal length and 5 mm aperture gives a spot diameter of about 2.6 µm.

Beam Characterization

Estimate the diffraction-limited spot size to compare with actual measured spot sizes, assessing the quality of an optical setup.

Example: If your measured spot is larger than the calculated Airy diameter, your system may have aberrations.

Frequently Asked Questions

What is the Airy spot diameter?
The Airy spot diameter is the diameter of the central bright spot in the diffraction pattern of a circular aperture, given by 2.44 * wavelength * focal length / aperture diameter. It represents the minimum focused spot size for a perfect, diffraction-limited system.
How is the laser spot size calculated?
The calculator uses the formula for the Airy disk diameter: D = 2.44 * λ * f / d, where λ is the wavelength, f is the focal length, and d is the aperture diameter. All inputs must be in meters.
What does diffraction-limited mean?
Diffraction-limited means the optical system is perfect, with no aberrations, so the focused spot size is limited only by diffraction. The Airy spot diameter is the theoretical minimum spot size for a given wavelength and aperture.

Tips & Common Mistakes

Tips

  • Ensure all input values are in meters (m) to get the spot diameter in meters.
  • Use consistent units: convert nanometers to meters by multiplying by 1e-9.
  • The formula assumes a circular aperture and uniform illumination; real beams may have different profiles.
  • For Gaussian beams, the spot size is often defined differently (1/e² radius), so this calculator is specific to Airy patterns.

Common Mistakes to Avoid

  • Forgetting to convert wavelength from nanometers to meters, leading to incorrect results.
  • Using the aperture radius instead of the diameter in the formula.
  • Assuming the result is the radius, but the calculator outputs the full diameter of the Airy spot.

Last updated: August 13, 2026