Smart Drill Size Finder — Fractional, Number, Letter & Metric Cross-Reference

How It Works

1. Enter Any Drill Size

   Type a drill size in any format: "3/16" for fractional, "#29" for number, "F" for letter, "5.0mm" for metric, or "0.1875" for decimal inches. Auto-detection handles the rest.

2. View Decimal Equivalents

   See the drill diameter in decimal inches and millimeters with nearest standard drill and deviation.

3. Check All Four Systems

   Result panel shows nearest match in fractional, number, letter, and metric systems with deviations.

4. Review Neighbors Table

   See the 3 drills smaller and 3 drills larger regardless of system, sorted by decimal diameter.

5. Cross-Reference Tap Drills

   Tap drill reference shows which drills serve as tap drills for 27 common thread sizes.

Built For

• Machinists converting between number, letter, fractional, and metric drill sizes
• CNC programmers looking up decimal equivalents for drill call-outs on older drawings
• Tool crib operators identifying unlabeled drills by measured diameter
• Maintenance mechanics finding substitute drill sizes from available inventory
• Engineering students learning the four drill size systems
• Purchasing agents cross-referencing drill sizes across suppliers

Features & Capabilities

Smart Input Parser

Auto-detects fractional, number, letter, metric, and decimal formats. Just type and it figures out the system.

570+ Drill Database

28 fractional, 60 number, 26 letter, and metric drills from 0.5mm to 25mm. Complete standard coverage.

Neighbors Table

3 drills smaller and 3 larger sorted by decimal diameter across all systems.

Tap Drill Cross-Reference

27 common thread sizes linked to standard tap drills with automatic flagging.

Full Filterable Chart

Browse complete database sorted by diameter with columns for all four naming systems.

PDF Export

Export results as a branded PDF for toolbox reference or job documentation.

Assumptions

• Fractional drill sizes in 1/64-inch increments from 1/64 to 1 inch per ASME B94.11M
• Number drill sizes #1 through #60 per ANSI standard wire gauge drill numbering
• Letter drill sizes A through Z per ANSI letter drill designations
• Metric drill sizes in 0.1mm increments from 0.5mm to 25mm per ISO 235
• Nearest-match algorithm finds the drill with smallest absolute deviation from the target diameter
• Tap drill cross-reference assumes 75% thread engagement per conventional shop practice

Limitations

• Actual drill diameters vary by manufacturer tolerance class (per ASME B94.11M, up to +0.003 inch for standard drills)
• Worn or resharpened drills may cut oversize by 0.001-0.005 inches beyond nominal
• Drill database covers standard sizes only; jobber, stub, and extra-length drills have the same diameters but different length specifications
• Does not include spade drill, indexable drill, or specialized core drill sizes
• Sub-millimeter metric drills (below 1mm) may not be available from all suppliers
• Tap drill recommendations are for cutting taps only; form taps require different pilot hole sizes

References

• ASME B94.11M - Twist Drills (standard drill diameters, tolerances, and length specifications)
• ANSI/ASME B94.11M - Number and Letter Drill Size Designations
• ISO 235 - Twist Drills with Parallel Shanks (metric drill specifications)
• Machinery's Handbook, 31st Edition - Drill Size Tables and Cross-Reference Charts
• ASME B1.1 - Unified Inch Screw Threads (tap drill sizing basis)
• ANSI B212.15 - High-Speed Steel Twist Drill Blanks (diameter tolerances by size range)

Frequently Asked Questions