Ball-cratering thin film thickness calculator. Measure the crater ring diameters and CaloCalc does the rest. 1- and 2-layer coatings, inch or mm in, μm and nm out.
Enter crater ring diameters as measured under the optical microscope.
Results
t = (b² − a²) / 8R
Session log
How it works
A precision steel ball (10–40 mm diameter) is rotated against the coated surface under a controlled abrasive slurry, grinding a spherical cap crater that cuts through the coating down to the substrate.
The crater is examined under an optical microscope. Each layer interface appears as a concentric ring — measure the diameter of each ring. Typical crater diameters are 0.5–4 mm.
a = inner ring (substrate)
b = outer ring (film surface)
or middle (2-layer)
Film thickness follows from the spherical cap geometry. The approximation holds for any practical PVD, CVD, or electroplated coating where film thickness is far less than ball radius.
t = (b² − a²) / 8R
t₁ = (b² − a²) / 8R
t₂ = (c² − b²) / 8R