Alkoc Labs
Home/Tools/Metric Tap Drill Calculator
DESIGN & MANUFACTURING

A starting point for your tap drill.

Estimate a pre-drill diameter for metric cutting taps. Keep the approximation and its limits visible.

No installation or accountCalculated in this tabCopy or download your result

01 · Your inputs

Cutting taps only. This D − P estimate is not a manufacturer-approved drill selection. Do not use it for forming taps or threaded inserts.

Axial distance between neighbouring thread crests, not threads per inch.

Decimal point or comma and scientific notation accepted. No thousands separators. Results update as you type.

02 · Your result

Ready to calculate

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Illustrative geometry; numerical results are listed below.
Calculated values — display rounded to up to 15 significant digits

Inputs stay in this tab. Nothing is uploaded or saved automatically.

Understand the calculation

Formula & assumptions
Approximate drill diameter = D − P
Inches = millimetres / 25.4

Enter your metric thread diameter and pitch. The familiar M8 × 1.25 example gives an approximate 6.75 mm opening; select an actual drill only after checking the tap manufacturer’s recommendation.

    Sources & limitations

    No thread-percentage claim, standard-combination validation or material-specific recommendation is made. Forming taps require a different, carefully controlled pre-hole.

    Alkoc Labs calculation engine v0.4.0. Educational and preliminary engineering use; independently verify inputs and results for consequential decisions. Display precision is not measurement uncertainty.

    Keep your next step simple.

    Need a different unit? Open the engineering unit converter. Have a measurement series to present? Open Graph Studio. Browse all tools →

    JSON exports include inputs, units, results, assumptions and source links. They do not contain your files or browser history. Inputs are lost when this tab is closed or reloaded; export anything you need to keep.