Hole Size Calculator

When to use this CAD/mechanical design tool

• Use while preparing CAD holes before drawing callouts.
• Use before the Hole and Thread Callout Helper.
• Use when comparing close, normal, and free clearance choices.

How to use

1. Enter one mechanical-design case using typed dimensions, counts, RPM values, tolerances, or drafting selections.
2. Click the exact action button for the selected tool; default values, typing, URL-prefilled values, and worked examples do not generate results automatically.
3. Review the output cards, warnings, assumptions, visual summary, copy text, and downloads before using the result in CAD, drawing, supplier, or inspection workflow.
4. Verify final values against applicable standards, supplier catalogs, validated CAD documentation, manufacturing limits, inspection practice, and qualified engineering review.

Input guide

Nominal fastener diameter

Diameter basis for clearance, pilot, dowel, or custom hole estimate.

Fit purpose

Close, normal, free, pilot, dowel, or custom planning mode.

Tolerance allowance

Optional non-negative extra allowance for review.

Notation

Output interpretation

• Estimated hole diameter is a planning value.
• The review range is not a standard tolerance grade.
• Dowel and pilot modes need standards and supplier verification.

Supported CAD/mechanical design use cases

• typed nominal size planning
• simple clearance classes
• pilot and dowel preliminary checks

Unsupported patterns

• thread tables
• reamer selection
• press-fit standards
• hole-position tolerance
• supplier-approved drill charts

How to interpret the output

• Free clearance increases assembly ease but reduces location control.
• Close clearance may need tighter manufacturing and inspection control.
• Dowel fits are not safely defined by a generic allowance alone.

CAD and mechanical-design guidance

• Use standards and supplier tables for final hole sizes.
• Coordinate clearance with tolerance stack-up and assembly process.
• Add clear drawing callouts for depth, quantity, finish, and inspection.

Worked examples

Assumptions

• Inputs are typed planning values and are not extracted from CAD files, supplier catalogs, drawings, PLM, CAM, ERP, or inspection systems.
• Metric calculations use millimetres unless the output explicitly states another unit; inch calculations use inches unless the output explicitly states another unit.
• The result is a preliminary calculator or drafting helper and not a certified standards database, CAD kernel, inspection report, or supplier approval.
• Simple allowance rules are used for planning.
• No material, process, drill-series, reamer, or thread-standard table is embedded.

Practical guidance

• Use Thread Size Calculator for thread geometry.
• Use Hole and Thread Callout Helper for drawing note text.

Common mistakes

• Treating a clearance estimate as a tap drill.
• Ignoring tolerance stack-up and fastener position.
• Not distinguishing close, normal, and free clearance intent.

Limitations

• No ISO fit table, ANSI clearance table, tap-drill table, reamer catalog, process capability, or inspection tolerance is included.
• ScholarTool CAD and mechanical-design calculators provide general engineering calculation and planning support. They do not replace supplier requirements, certified standards, CAD software documentation, manufacturing review, inspection standards, or professional engineering judgement.
• The tool does not open, upload, parse, repair, or validate CAD files, drawings, STEP, STL, DXF, DWG, CAM, or CNC data.
• The tool does not perform strength certification, fatigue validation, finite-element analysis, supplier catalog selection, standards compliance certification, or inspection programming.

Related workflow links