Anodizing Dimension Change Calculator
Estimate how much anodizing changes part dimensions: growth per surface, outside diameter, bore and thread allowance for Type II and Type III (hard) anodizing.
About half of an anodic layer grows into the metal and half builds up on the surface, for both decorative (Type II) and hard (Type III) anodizing. Confirm the ratio with your anodizer.
Typical coating thickness
- Decorative / Type II anodizing: usually about 5–25 µm.
- Hard / Type III anodizing: usually about 25–75 µm.
Because the layer grows on every surface, an outside diameter gets larger by about one coating thickness and a bore gets smaller by the same amount. Threads, bearing seats and press fits often need machining allowance or masking. State on the drawing whether dimensions apply before or after anodizing.
FAQ
How much does anodizing add to a part?
About half the coating thickness per surface. A 20 µm coating adds about 10 µm per surface, so a diameter grows by about 20 µm.
Do threads need masking for anodizing?
Often yes, or extra allowance, because the coating builds up on the flanks and can stop the mating part from fitting.