Finished Hole from Drill Size Calculator
Estimate PCB finished hole diameter after plating, or solve the matching drill size or one-wall plating thickness for via and component-hole checks.
Inputs and tolerance
Select the dimension to calculate, then describe the other two dimensions with percentage tolerance or explicit input ranges.
Range: 234m mm to 266m mm
All dimensions are entered in millimetres. Plating thickness is one-wall copper thickness, so it is subtracted from both sides of the drilled diameter.
Nominal result and range
Estimated finished diameter uses finished hole = drill diameter - 2 × plating thickness.
Finished hole diameter is estimated from nominal drill diameter minus plating on both hole walls. Real finished-hole limits depend on the fabricator drill tolerance, plating process, material movement, tool wear, and stated finished-hole specification.
Estimate the plated opening before checking fit and manufacturability
A plated PCB opening is smaller than the drilled diameter because copper is deposited on both barrel walls. Use this calculator for first-pass drill-to-finished-size checks before applying the fabricator tolerance table.
Component fit
Compare the resulting diameter with the lead size, positional tolerance, insertion allowance, and assembly process.
Via review
Use the finished diameter alongside aspect ratio, annular ring, plating call-out, and current requirements.
Drawing clarity
Confirm whether the drawing and fabrication notes specify drill size, finished size, or a finished-size tolerance.
Equation and limits
The nominal relationship is finished size equals drill diameter minus twice the one-wall plating thickness. The same relationship can estimate required drill diameter or implied plating thickness when two dimensions are known.
Nominal equation
Finished size ≈ drill diameter − 2 × plating thickness.
Tolerance range
Percentage tolerance and explicit input ranges are evaluated at the geometry corners for the selected solved dimension.
Process variation
Drill tolerance, copper distribution, tool wear, material movement, and supplier allowances are outside this simple estimate.
Worked example
Inputs: drill diameter = 0.30 mm, plating thickness = 0.025 mm on each wall.
Result: finished size = 0.30 mm − 2 × 0.025 mm = 0.25 mm.
Next check: compare the 0.25 mm result with the required lead or via size, then apply the fabricator finished-size tolerance.
Related calculators and next checks
Via current guide
Review barrel geometry, copper thickness, current sharing, heat, and fabricator limits.
Engineering conversion calculator
Convert PCB dimensions and mixed engineering units before entering values.
Finished-hole sizing guide
Review assumptions, worked examples, common mistakes, and next checks.
Engineering reference
Equations, assumptions, and design guidance
Estimates plated PCB finished-hole diameter from nominal drill diameter and one-wall plating thickness, and solves the same geometry for drill size or plating thickness.
Equations and variables
Dfinished = Ddrill - 2 * TplatingDdrill = Dfinished + 2 * TplatingTplating = (Ddrill - Dfinished) / 2- Dfinished
- Finished plated hole diameter (mm)
- Ddrill
- Nominal drill diameter (mm)
- Tplating
- One-wall hole plating thickness (mm)
Assumptions and limitations
Assumptions
- Plating thickness is applied equally to both sides of the drilled opening.
- Inputs are nominal dimensions unless the tolerance controls define a range.
- The hole remains circular enough for the scalar diameter estimate to be useful.
Limitations
- Fabricator drill tolerance, finished-hole tolerance, plating distribution, tool wear, material movement, and annular-ring requirements are not modelled.
- The result is a first-pass manufacturability estimate, not a fabrication acceptance limit.
Worked example and design use
0.30 mm drill with 25 micrometre plating
Inputs: Ddrill = 0.30 mm, Tplating = 0.025 mm
Outputs: Dfinished = 0.25 mm
Design guidance
- Check the fabricator capability table and drawing notes before relying on a nominal drill-to-finished-hole conversion.
- Compare the finished-hole range with component lead diameter, via aspect ratio, annular ring, and assembly allowance.