Annular Ring Calculator
Worst-case annular ring from pad, hole and fab allowance — pass/fail against your minimum and the pad size needed to fix it.
“Finished hole” is after plating — the drill is ~0.1 mm larger. IPC Class 2 (most commercial work) actually tolerates some breakout on external layers; Class 3 (high-rel) requires ≥ 0.05 mm ring all round. Via-in-pad and teardrops are the standard escapes when this check fails on dense BGA fanout.
Annular Ring Calculator computes the worst-case copper ring left around a drilled hole after fab tolerances — free, instant and private in your browser. Designers pushing BGA fanout density and anyone whose fab flagged annular-ring DRC errors use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Annular Ring Calculator
Annular Ring Calculator computes the worst-case copper ring left around a drilled hole after fab tolerances using the standard engineering relation: ring = (padØ − holeØ)/2 − allowance/2, checked against your minimum; pad needed = hole + 2·ring + allowance. Worked live: a 1.0 mm pad on a 0.5 mm hole with 0.2 mm fab allowance leaves a 0.15 mm worst-case ring — passes a 0.125 mm minimum. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Annular Ring Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Annular Ring Calculator?
- ✓Implements the real formula — ring = (padØ − holeØ)/2 − allowance/2, checked against your minimum — with the substitution shown, not a black box
- ✓Built for designers pushing BGA fanout density and anyone whose fab flagged annular-ring DRC errors
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate annular ring?+
The worst-case copper ring left around a drilled hole after fab tolerances follows ring = (padØ − holeØ)/2 − allowance/2, checked against your minimum; pad needed = hole + 2·ring + allowance. For example, a 1.0 mm pad on a 0.5 mm hole with 0.2 mm fab allowance leaves a 0.15 mm worst-case ring — passes a 0.125 mm minimum. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
What annular ring do PCB fabs require?+
Standard service commonly wants ≥ 0.125 mm (5 mil) after their drill/registration allowance (~0.2 mm); advanced services accept 0.05 mm with tighter allowances. IPC Class 2 even tolerates some breakout on external layers — Class 3 demands ≥ 0.05 mm intact ring.
My BGA fanout fails the ring check — what are the escapes?+
Teardrops add copper exactly where misregistration bites; smaller finished holes (0.2–0.25 mm) free pad area; and via-in-pad with filling/capping removes the dogbone entirely. Each costs a little money — teardrops are free, via-in-pad is not.
Is the Annular Ring Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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