Finished hole, drill size, and plating thickness
A plated through-hole is smaller after fabrication than the nominal drill because copper plating builds on both barrel walls.
Reviewed 23 June 2026
How do drill size and plating thickness affect finished PCB hole diameter?
For a first-pass estimate, subtract twice the one-wall plating thickness from the drill diameter. The result is only a nominal geometry estimate because real finished-hole size also depends on drill tolerance, plating distribution, material movement, and the fabricator finished-hole specification.
Model summary
- Finished hole diameter: Dfinished = Ddrill - 2 * Tplating.
- Required drill diameter: Ddrill = Dfinished + 2 * Tplating.
- Implied one-wall plating thickness: Tplating = (Ddrill - Dfinished) / 2.
Worked example
For a 0.30 mm drill and 0.025 mm plating on each wall, subtract 0.050 mm from the drill diameter.
The estimated finished hole is 0.30 mm - 2 * 0.025 mm = 0.25 mm.
If the component lead or via requirement is close to 0.25 mm, use the fabricator finished-hole tolerance rather than relying on the nominal value alone.
Practical sequence
Estimate the nominal finished hole, apply the supplier finished-hole tolerance, then check lead fit, annular ring, minimum web, aspect ratio, and plating call-out together.
Fabrication drawing note
State whether the drawing calls out finished hole sizes or tool drill sizes. For plated holes, fabricators commonly expect finished size requirements and then choose the drill process that meets them.
Common mistakes
- Treating drill diameter as the finished plated opening.
- Forgetting that plating is present on both hole walls.
- Checking lead fit without annular ring, positional tolerance, aspect ratio, and fabricator capability.
When the approximation breaks down
- The simple model assumes uniform plating and a circular hole.
- Drill tolerance, desmear, plating distribution, tool wear, material movement, and supplier process limits can move the real finished dimension.
Further checks and references
- Ask the PCB fabricator for minimum finished hole, drill tolerance, plating thickness, annular ring, and aspect-ratio capability.
- For component holes, include lead diameter, lead tolerance, positional tolerance, assembly allowance, and plating tolerance.
- For vias, include board thickness, plating thickness, via barrel resistance, current sharing, thermal environment, and manufacturability.
