How thick is zinc plating?

Between 5 and 50 µm depending on the service class. ASTM B633 SC1 is 5 to 8 µm for indoor use, SC2 is 8 to 13 µm for general commercial service, and SC4 is 25 to 50 µm for severe exposure. Hot-dip galvanizing is far thicker at 45 to 100 µm.

Does plating change the dimensions of a part?

Yes — an electroplated coating adds its full thickness to each surface, so a shaft grows by twice the coating thickness in diameter. Threads and close fits need allowance for this, which is what the 6g metric thread class provides. Mask features that cannot tolerate the growth.

How much does anodizing grow a part?

Roughly half the coating thickness per surface, because anodizing converts the base aluminium into oxide rather than depositing material on top. A 25 µm Type II coating grows the part about 12 µm per surface; a 100 µm hard anodize grows it about 50 µm — enough to close a fit.

What is the difference between Type II and Type III anodizing?

Type II is the standard sulfuric anodize at 5 to 25 µm, used for appearance, corrosion protection and dyeing. Type III is hard anodizing at 25 to 100 µm, harder and more abrasion resistant but more brittle and darker, and it grows the part much more.

Why must high-strength steel be baked after plating?

Because electroplating generates hydrogen that can diffuse into the steel and cause hydrogen embrittlement — delayed cracking under load. Parts above roughly 1,000 MPa tensile must be baked shortly after plating to drive the hydrogen out. Above 1,200 MPa, mechanical coatings are preferred over electroplated ones.

How thick is powder coating?

Typically 50 to 150 µm, several times thicker than most plating. That thickness matters because it can bridge small gaps and will not fit into threads or close-tolerance features, which must be masked before coating.

Coating Thickness Chart

Typical thickness ranges for fifteen coatings from 0.25 µm decorative chrome to 500 µm hard chrome, with what each one does to the part's dimensions.

Data verified 2026-09-29 · based on ASTM B633-23

Find a coating

Coating Thickness Ranges

Coating^[2]	Minimum µm^[2]	Maximum µm^[2]	Typical use^[2]	Notes^[2]
Zinc electroplating (ASTM B633 SC1) #	5	8	Decorative and light-duty corrosion protection indoors	The thinnest commercial zinc coating. Adequate indoors, insufficient for outdoor exposure.
Zinc electroplating (ASTM B633 SC2) #	8	13	General indoor and sheltered outdoor service	The common commercial plating thickness for fasteners and brackets.
Zinc electroplating (ASTM B633 SC3) #	13	20	Outdoor exposure, moderate corrosion	Where the part will see weather but not salt or chemicals.
Zinc electroplating (ASTM B633 SC4) #	25	50	Severe outdoor and industrial exposure	The thickest electroplated zinc. Requires baking after plating to avoid hydrogen embrittlement on high-strength steel.
Hot-dip galvanizing (ASTM A123) #	45	100	Structural steel outdoors, 20–50 year service	Much thicker than electroplating and metallurgically bonded, giving far longer life. Thickness varies with steel section — thicker sections get thicker coatings.
Electroless nickel (ASTM B733) #	10	50	Wear resistance with corrosion protection, uniform on complex shapes	Deposits evenly on any shape, unlike electroplating which favours edges and high-current areas.
Electroplated hard chrome #	25	500	Wear resistance on shafts, hydraulic rods, moulds	Applied heavily to rebuild worn dimensions as well as for wear resistance. Requires grinding after plating.
Decorative chrome over nickel #	0.25	0.8	Appearance with corrosion protection underneath	The chrome layer is a thin flash over a much thicker nickel deposit — the nickel does the corrosion protection.
Anodizing Type II (MIL-A-8625) #	5	25	Aluminium appearance, corrosion protection, dyeing	The standard sulfuric anodize. Grows the part by roughly half the coating thickness per surface.
Hard anodizing Type III (MIL-A-8625) #	25	100	Aluminium wear resistance, abrasion	Thicker and harder but more brittle and darker than Type II. Grows the part substantially — significant on threads and close fits.
Black oxide #	0.5	2	Dimensional stability, mild corrosion protection with oil	Barely changes dimensions, which is why it is used where a coating cannot be tolerated. Requires oil to provide corrosion protection.
Powder coating #	50	150	Durable finish on fabricated parts	Applied thickly by comparison with plating. Mask threads and close-tolerance features.
Wet paint (liquid) #	25	75	General protective and decorative finish	Thickness is specified as dry film thickness, not wet.
PVD coating (TiN, TiAlN, CrN) #	2	5	Cutting tools, wear surfaces, decorative	Very thin but extremely hard. Applied by physical vapour deposition at relatively low temperature.
CVD coating #	5	20	Cutting tools, high-temperature wear surfaces	Thicker and harder than PVD but applied at high temperature, which limits the substrates it can be used on.

Most coatings grow the part, and the growth is one-sided where it matters. An electroplated coating is deposited on the surface, so it adds its full thickness to each dimension — a 13 µm zinc coating on a shaft makes it 26 µm larger in diameter because both sides are coated.

Anodizing is different and worse. It converts the base metal into oxide rather than depositing on top, so the part grows by roughly half the coating thickness per surface while also consuming aluminium. On a hard-anodized 100 µm coating that means about 50 µm growth per surface — enough to close a thread or an interference fit completely.

The practical consequences are the same in both cases: threads must have allowance for coating, which is what the 6g thread class provides on metric fasteners, and close-tolerance features should be masked or machined after coating. Where a part must be coated and still hold a tolerance, the drawing should state the pre-coating dimension and the coating thickness rather than a single finished dimension, so the shop can allow for the growth rather than guessing.

One warning worth carrying: electroplating can cause hydrogen embrittlement in high-strength steel, which is why parts above roughly 1,000 MPa tensile must be baked after plating, and why 12.9 property class bolts are normally supplied with a mechanical coating rather than an electroplated one.

Choosing a Coating by What It Must Survive

Corrosion protection scales broadly with thickness, but the mechanism matters as much as the number.

Zinc coatings protect by sacrificing themselves — the zinc corrodes in place of the steel, including at scratches and cut edges where a barrier coating would fail. That is why galvanising works so well on structural steel and why its life is set by thickness and environment rather than by the quality of the surface preparation.

Barrier coatings protect by excluding the environment — paint, powder coat and the nickel under decorative chrome. They fail at any breach, so their performance depends entirely on surface preparation and on avoiding damage. A scratch in a powder coat is a corrosion site; a scratch in galvanising is protected by the surrounding zinc.

Anodizing is a conversion coating on aluminium and behaves as a hard, inert barrier. It is not sacrificial — anodized aluminium does not protect bare aluminium next to it.

Wear coatings are a separate question from corrosion. Hard chrome, electroless nickel, hard anodizing and PVD all exist primarily for abrasion resistance, and their corrosion performance is incidental. Selecting on hardness and then checking corrosion resistance is the right order for those.

Frequently Asked Questions

How thick is zinc plating?: Between 5 and 50 µm depending on the service class. ASTM B633 SC1 is 5 to 8 µm for indoor use, SC2 is 8 to 13 µm for general commercial service, and SC4 is 25 to 50 µm for severe exposure. Hot-dip galvanizing is far thicker at 45 to 100 µm.
Does plating change the dimensions of a part?: Yes — an electroplated coating adds its full thickness to each surface, so a shaft grows by twice the coating thickness in diameter. Threads and close fits need allowance for this, which is what the 6g metric thread class provides. Mask features that cannot tolerate the growth.
How much does anodizing grow a part?: Roughly half the coating thickness per surface, because anodizing converts the base aluminium into oxide rather than depositing material on top. A 25 µm Type II coating grows the part about 12 µm per surface; a 100 µm hard anodize grows it about 50 µm — enough to close a fit.
What is the difference between Type II and Type III anodizing?: Type II is the standard sulfuric anodize at 5 to 25 µm, used for appearance, corrosion protection and dyeing. Type III is hard anodizing at 25 to 100 µm, harder and more abrasion resistant but more brittle and darker, and it grows the part much more.
Why must high-strength steel be baked after plating?: Because electroplating generates hydrogen that can diffuse into the steel and cause hydrogen embrittlement — delayed cracking under load. Parts above roughly 1,000 MPa tensile must be baked shortly after plating to drive the hydrogen out. Above 1,200 MPa, mechanical coatings are preferred over electroplated ones.
How thick is powder coating?: Typically 50 to 150 µm, several times thicker than most plating. That thickness matters because it can bridge small gaps and will not fit into threads or close-tolerance features, which must be masked before coating.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASTM A123/A123M — Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products	standard	ASTM A123/A123M-17
[2]	ASTM B633 — Electrodeposited Coatings of Zinc on Iron and Steel	standard	ASTM B633-23
[3]	ASTM B689 — Electroplated Engineering Nickel Coatings	standard	ASTM B689-97(2018)
[4]	ASTM B733 — Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal	standard	ASTM B733-22
[5]	ISO 7599 — Anodizing of aluminium and its alloys	standard	ISO 7599:2018
[6]	MIL-A-8625 — Anodic Coatings for Aluminum and Aluminum Alloys	standard	MIL-A-8625F

Data Sources

Standard	Revision	What it covers on this page
ASTM B633 — Electrodeposited Coatings of Zinc on Iron and Steel	ASTM B633-23	the zinc plating service classes SC1 to SC4
ASTM A123/A123M — Zinc (Hot-Dip Galvanized) Coatings	ASTM A123/A123M-17	the hot-dip galvanizing thickness requirements
MIL-A-8625 — Anodic Coatings for Aluminum and Aluminum Alloys	MIL-A-8625F	the Type II and Type III anodize thicknesses
ASTM B733 — Autocatalytic Nickel-Phosphorus Coatings	ASTM B733-22	the electroless nickel thickness classes

Cross-checked against:

Coating thicknesses checked against the governing specification for each finish
The dimensional growth of anodizing verified against the conversion mechanism — growth is about half the coating thickness per surface
Thickness ranges cross-checked between two coating suppliers' published capability tables
Four values held as known-value checks spanning the thinnest and thickest finishes

Thickness ranges are typical for the finish; the governing specification sets the acceptance limits, and those vary with the service class and the substrate. Coating growth must be allowed for on threads and fits, and high-strength steel requires post-plating baking to avoid hydrogen embrittlement.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

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Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Coating Thickness Chart." https://refmanual.com/charts/coating-thickness/ (accessed 2026-09-29). Data from ASTM B633 — Electrodeposited Coatings of Zinc on Iron and Steel, ASTM B633-23.

BibTeX

@misc{coating-thickness,
  title        = {Coating Thickness Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/coating-thickness/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASTM B633 — Electrodeposited Coatings of Zinc on Iron and Steel, ASTM B633-23}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Coating Thickness Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/coating-thickness/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASTM B633 — Electrodeposited Coatings of Zinc on Iron and Steel, ASTM B633-23
ER  -

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