Coating thickness dimension calculator
Powder coat, paint, plating and PVD all sit on top of the surface, so every coated face grows. Enter the coating thickness and one dimension to see the finished size, or flip the direction to get the size to machine before coating.
Typical: 60 to 120 micron per surface
Scope of this tool. It treats coating thickness as a nominal, evenly distributed value on every surface. Real deposits vary: electroless nickel is the most uniform and follows the geometry closely, while tank plating builds thicker on corners and projections and thinner inside recesses, and powder coat runs thicker in corners and internal channels. Use the results for sizing decisions and drawing notes, and check any certified dimension against your own gauging after the parts come back.
Why coatings move dimensions at all
Finishes fall into two families, and they behave differently on a drawing. Additive coatings deposit new material on top of the surface, so the part gets bigger by the full coating thickness on every coated face. Powder coat, wet paint, electroless nickel, zinc plating, hard chrome and PVD all work this way.
Conversion coatings grow out of the base metal itself. Black oxide is the common one for steel: the layer forms partly by consuming the surface, so only about half the layer thickness shows up as growth. Anodizing is the other well known case, with roughly half the layer growing into the metal and half outward, and it has its own anodizing dimension calculator because the pre-machining compensation works differently.
- External diameter: grows by twice the per-surface growth, one growth layer on each side.
- Bore: closes by the same amount. A bore that gauged correctly bare can bind on a pin after coating.
- Length between two coated faces: grows by two growth layers, one per face.
- Threads: coating closes the thread form. Under about 10 micron of deposit threads usually still run, above that they need masking or a thread chase.
Typical thickness by coating
| Coating | Typical per surface | Behaviour | Common use on CNC parts |
|---|---|---|---|
| Powder coating | 60 to 120 micron | Additive | Enclosures, brackets, covers needing durable colour |
| Wet paint | 20 to 40 micron | Additive | Cosmetic panels, matched colour sets |
| Electroless nickel | 10 to 50 micron | Additive, very uniform | Corrosion and wear on complex geometry, threaded parts |
| Zinc plating | 5 to 25 micron | Additive | Steel corrosion protection, fasteners, fittings |
| Hard chrome | 25 to 250 micron | Additive | Wear surfaces, hydraulic rods, repair build-up |
| PVD | 1 to 5 micron | Additive, line of sight | Hard, thin films on tooling and premium consumer parts |
| Black oxide | 0.5 to 2 micron | Conversion, half grows out | Low reflective steel, light corrosion protection with oil |
The thickness value on a purchase order can mean the layer on one surface or the total build across a diameter, and suppliers do not use one convention. State it as per surface on the drawing to remove the doubt. Our powder coating and electroless nickel pages list the thickness ranges we run in production.
Coating and fits on the same drawing
A coating shift that is small next to a general tolerance can still kill a specific fit. A 25 micron electroless nickel layer closes a bore by 50 micron across the diameter, which is larger than the whole tolerance band on an H7 hole. When a coated feature must keep a precise fit, there are three ways out, and drawings usually pick one of them.
- Mask the feature. Threads, dowel holes, bearing seats and grounding faces get masked or plugged before the parts go into the tank.
- Pre-size the feature. Machine the bore oversize so the coating brings it back into band. The calculator above gives that pre-coating target directly.
- Machine after coating. For hard chrome and some plating, the surface is ground to final size after deposition, which costs more but removes the uncertainty.
For the numbers behind the fits themselves, the ISO tolerance fit calculator returns hole and shaft limits for any H7/g6 style call, so you can check how much of the tolerance band the coating consumes.
Questions that come up
Does powder coating change dimensions?
Yes, and more than most people expect. Powder coat builds 60 to 120 micron per surface, so a coated face pair moves a dimension by 120 to 240 micron. That closes threaded holes, shifts press fits and swallows a 0.1 mm tolerance entirely. Threads and tight features get masked; the rest of the part takes the build-up into account at machining time.
How much does PVD coating add to size?
One to five micron per surface for common TiN, CrN and DLC films. On most CNC dimensions that is inside the tolerance band, which is one reason PVD suits finished components and cutting tools. Mating surfaces with micron level fits still need checking, and the film reproduces the surface underneath, so polish before coating if the finish matters. Our PVD coating service page covers film types and thickness control.
Is electroless nickel thickness uniform on complex parts?
Close to it, and that is its main advantage over tank plating. Because the deposit is chemical rather than electric, current shadows and Faraday effects do not apply, so deep pockets and internal threads plate nearly as thick as open faces. Specify the thickness per surface and the shop targets the middle of that band.
What about anodizing?
Anodizing grows half into the metal and half out, so the compensation maths differs from the coatings on this page. Use the dedicated anodizing dimension calculator for Type II and Type III, and the thickness and tolerance guide for how the two interact on production parts.
Should the drawing measure before or after coating?
Say it explicitly. The cleanest convention is to dimension and tolerance everything after finishing, and put the coating callout with its thickness on the drawing. If a dimension only applies bare, flag it as machined size before coating. Ambiguity here is the single most common cause of rework on coated parts, and it costs nothing to write down.
How do I keep a bore within size after plating?
Three routes, in order of cost: leave the bore uncoated by masking, machine it oversize by twice the expected deposit and let the plating bring it back, or plate the whole part and finish the bore afterwards. For steel parts the choice between zinc and electroless nickel usually comes down to whether the bore carries a fit, since zinc distribution is less uniform. Our zinc plating guide and the hard chrome versus electroless nickel comparison cover the trade-offs.
