Lens Focal Length Calculator
Calculate the focal length of a lens using the lensmaker's equation with refractive index and curvature radii
About this calculator
The Lens Focal Length Calculator determines the focal length of a lens using the fundamental lensmaker's equation, which relates the lens's refractive index and the curvature radii of its surfaces. This tool is essential for optical engineers, physics students, and lens designers who need to predict how light will converge or diverge through a lens system. By inputting the material's refractive index and the radius of curvature for both lens surfaces, you can accurately calculate the focal length needed for your optical applications.
How to use
Enter the refractive index of the lens material (typically between 1.3-1.9 for common optical materials). Input the radius of curvature for the first surface (R1) and second surface (R2) in your preferred units. Use positive values for convex surfaces and negative for concave surfaces. Click calculate to get the focal length result.
Frequently asked questions
What is the lensmaker's equation?
The lensmaker's equation relates focal length to refractive index and surface curvatures: 1/f = (n-1)(1/R1 - 1/R2), where f is focal length, n is refractive index, and R1, R2 are curvature radii.
How do I determine the sign of radius values?
Use positive radius values for convex surfaces (curving outward from the lens center) and negative values for concave surfaces (curving inward toward the lens center).
What refractive index should I use for common materials?
Common values include: crown glass (1.52), flint glass (1.62), acrylic (1.49), and polycarbonate (1.59). Check material specifications for precise values at your operating wavelength.