Gold Plating Thickness Guide — Microns and Microinches

Thickness is the single most important number in any gold plating specification. It determines how long the deposit lasts, whether it meets a legal marking standard, what it costs, and whether it passes inspection. This guide covers the units, the standards, the typical ranges by application, and how thickness is actually measured.

How is gold plating thickness measured and expressed?

Gold plating thickness is expressed in microinches (millionths of an inch) in U.S. industry and in microns (micrometers) internationally, and it is measured non-destructively by X-ray fluorescence. The conversion is fixed: 1 micron equals 39.37 microinches.

Handy reference points:

| Microns | Microinches | Common name | | --- | --- | --- | | 0.05 | 2 | Flash / wash | | 0.175 | 7 | FTC minimum for "gold electroplate" | | 0.5 | 20 | FTC minimum for "gold plated" | | 1.0 | 39 | Good commercial decorative | | 2.5 | 100 | FTC "heavy gold plated"; MIL Class 2 | | 5.0 | 200 | MIL Class 3, heavy engineering |

X-ray fluorescence (XRF) reads thickness in seconds without touching the deposit, which is why it is the universal production and certification method. Cross-sectioning and coulometric (destructive) methods exist for arbitration but are rarely needed.

What do the FTC rules say about gold plating thickness on jewelry?

Under the FTC Jewelry Guides, thickness determines what a seller may legally call a gold-plated item: "gold electroplate" requires at least 0.175 micron (about 7 microinches) of fine gold, "gold plated" or "gold electroplated" in general trade practice means at least 0.5 micron (20 microinches), and "heavy gold electroplate" requires 2.5 microns (about 100 microinches).

Anything thinner than 0.175 micron must be described as "gold flashed" or "gold washed." These rules exist because thickness is invisible to the buyer: a 2-microinch flash and a 100-microinch heavy deposit look identical at the counter and differ in lifespan by two orders of magnitude. If you are comparing plated pieces against solid gold or gold-filled goods, the marking distinctions are unpacked in gold plated vs solid gold.

What thickness classes do MIL-SPEC and ASTM standards define?

MIL-G-45204 and ASTM B488 specify thickness by Class, from Class 00 at 20 microinches up to Class 6 at 1,500 microinches. Purity (Type) and hardness (Code) are specified separately, so a complete callout reads like "ASTM B488, Type II, Code C, Class 1."

The class ladder:

Class 00 — 20 microinches (0.5 micron)
Class 0 — 30 microinches (0.75 micron)
Class 1 — 50 microinches (1.25 microns)
Class 2 — 100 microinches (2.5 microns)
Class 3 — 200 microinches (5 microns)
Class 4 — 300 microinches (7.5 microns)
Class 5 — 500 microinches (12.5 microns)
Class 6 — 1,500 microinches (37.5 microns)

Classes 0 through 2 cover the overwhelming majority of connector and instrument work. The classes above that serve specialized wear, brazing, and reflectivity applications. The standards also define the "significant surface" — the functional area where minimum thickness must be met — because plated thickness naturally varies across part geometry.

How thick should gold plating be for each application?

As a working rule: 5 to 10 microinches for light decorative use, 20 to 40 microinches for quality jewelry and daily-handled items, 30 to 50 microinches for connector contacts, and 50 to 200 microinches for harsh-environment, medical, and aerospace service.

Application benchmarks:

Costume and fashion pieces: 3 to 10 microinches — attractive, short-lived
Quality jewelry, watch cases, giftware: 20 to 40 microinches of 24K gold plating
Electronics connectors and edge contacts: 30 to 50 microinches hard gold over nickel
High-reliability aerospace and defense: 50 to 100 microinches per program spec
Medical and implantable components: 50 microinches and up, high-purity soft gold
Reflectors and RF surfaces: thickness set by skin depth and emissivity requirements, often 100 microinches or more

Wear life scales roughly with thickness for a given hardness, so doubling thickness is the most direct way to buy service life.

Why not just plate everything extra thick?

Because gold is priced by mass, thickness is the dominant cost driver — doubling thickness roughly doubles the gold consumed on every square inch. Beyond cost, very heavy deposits can build internal stress, soften sharp decorative detail, and change dimensions on precision parts.

Engineering judgment means plating to the requirement plus a sensible margin, not to the maximum. On tight-tolerance components such as threads and press fits, added thickness is a dimensional change that must be accounted for in design. The economics are covered in more depth in gold plating cost factors.

Does underplating count toward gold thickness?

No — specified gold thickness means gold only, measured above any underplate. A typical engineered stack is 50 to 200 microinches of nickel beneath 30 to 50 microinches of gold, and the XRF measurement separates the layers.

The nickel underplate is not filler; it blocks copper diffusion into the gold, supports the thin gold layer against wear, and improves corrosion behavior at pores. A thin gold layer over proper nickel routinely outperforms a thicker gold layer plated directly on copper.

How do you verify you got the thickness you paid for?

Ask your plater for XRF thickness readings on the significant surfaces, referenced to the governing standard. Any professional lab measures thickness as part of process control and can report it; certification to ASTM B488 or MIL-G-45204 formalizes that reporting.

Our Vista, CA lab verifies every job by XRF and plates to your specified class or our recommendation, from single restoration pieces to high-volume production for clients between San Diego and Los Angeles. Tell us your target thickness — or let us recommend one — and we will price it transparently at $100 per square inch with a $500 minimum. Start with a free photo quote or call (760) 458-3299.