BIZOMAT MAKEOS · Manufacturing
Drill Sizes: Number, Letter, Fraction and Metric
What is the decimal size of this number or letter drill, or which drills are closest to a size?
Decimal inch and millimetre size of number (1–80) and letter (A–Z) drills, and the nearest number, letter, fractional (1/64) and metric (0.1 mm) drills to any diameter.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Look up | choice | Find drills near a size, or the size of a drill designation. |
| Diameter | mm or in | Required hole or drill diameter. |
| Unit of diameter | choice | Unit of the diameter. |
| Drill designation | choice | Number or letter drill to look up. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Look up
- What it is
- Whether to find the nearest number, letter, fractional and metric drills to a diameter, or to look up the decimal size of a number or letter drill.
- Units and format
- Choose one of 2 options from the list: Nearest drills to a diameter; Size of a number or letter drill.
- Example
- The form opens with “Nearest drills to a diameter” selected as a worked example. Choose the option that matches your case.
- Get it right
- Only Diameter and its unit are used in the first mode, and only the drill designation in the second.
What this means: Diameter
- What it is
- The hole or drill diameter you need, for example a tap drill size from a thread table or a clearance hole from a drawing.
- Units and format
- Enter a number in mm or in: millimetres or inches, as long as every length uses the same unit. The form accepts 0.000001 mm or in to 100 mm or in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6.8 mm or in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Choose the matching unit below; 6.8 read as inches would be a very different drill.
What this means: Unit of diameter
- What it is
- The unit the diameter is written in, millimetres or inches.
- Units and format
- Choose one of 2 options from the list: mm; in.
- Example
- The form opens with “mm” selected as a worked example. Choose the option that matches your case.
- Get it right
- Check this matches the diameter; inches here are decimal, so convert fractions first.
What this means: Drill designation
- What it is
- The number (No. 1 to No. 80) or letter (A to Z) drill designation whose decimal size you want. Number drills get smaller as the number rises; letter drills get larger from A to Z.
- Units and format
- Choose one of 106 options from the list: No. 1; No. 2; No. 3; No. 4; No. 5; No. 6; No. 7; No. 8; No. 9; No. 10; No. 11; No. 12; No. 13; No. 14; No. 15; No. 16; No. 17; No. 18; No. 19; No. 20; No. 21; No. 22; No. 23; No. 24; No. 25; No. 26; No. 27; No. 28; No. 29; No. 30; No. 31; No. 32; No. 33; No. 34; No. 35; No. 36; No. 37; No. 38; No. 39; No. 40; No. 41; No. 42; No. 43; No. 44; No. 45; No. 46; No. 47; No. 48; No. 49; No. 50; No. 51; No. 52; No. 53; No. 54; No. 55; No. 56; No. 57; No. 58; No. 59; No. 60; No. 61; No. 62; No. 63; No. 64; No. 65; No. 66; No. 67; No. 68; No. 69; No. 70; No. 71; No. 72; No. 73; No. 74; No. 75; No. 76; No. 77; No. 78; No. 79; No. 80; Letter A; Letter B; Letter C; Letter D; Letter E; Letter F; Letter G; Letter H; Letter I; Letter J; Letter K; Letter L; Letter M; Letter N; Letter O; Letter P; Letter Q; Letter R; Letter S; Letter T; Letter U; Letter V; Letter W; Letter X; Letter Y; Letter Z.
- Example
- The form opens with “No. 7” selected as a worked example. Choose the option that matches your case.
- Get it right
- Used only when looking up the size of a drill designation.
Method and formulas
- Number and letter drill sizes are the standard decimal equivalents (ASME B94.11M).
- Fractional drills in 1/64 in steps; metric drills in 0.1 mm steps.
- The closest drill in each series is reported with its difference from the required size.
- Example: the nearest drills to 6.8 mm are No. 1, Letter H, 17/64 in, 6.8 mm.
Limitations
- Drills cut slightly oversize; check the hole for close tolerances.
- Availability of sizes varies by supplier.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Find the size of a number or letter drill
- Find the nearest available drill to a calculated hole size
- Convert between drill series
Who it is for
- Machinists
- Toolmakers
- Maintenance fitters
What you get
- Nearest number, letter, fractional and metric drills
- Decimal size of a designation
- Difference from the required size
Interpreting the result
- For tapping, use the tap drill tool to choose the size first, then find the nearest drill here.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2695, 1015–1016. Topic reference; no source tables or recommended settings are reproduced.
- ASME B94.11M Twist Drills
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Open the Drill Sizes: Number, Letter, Fraction and Metric calculator