---
type: "drill-series"
series: "fractional"
name: "Fractional Drill Sizes"
size_count: 64
smallest: "1/64"
largest: "1"
range_in: "0.0156–1.0000"
range_mm: "0.397–25.400"
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/fractional
---

# Fractional Drill Sizes — All 64 Sizes in Inches and Millimetres

The fractional drill sizes series runs from 1/64 at 0.0156 in (0.397 mm) to 1 at 1.0000 in (25.400 mm), 64 sizes in all. Inch fractional drills in 1/64 in steps from 1/64 to 1 in.

- **Series**: Fractional Drill Sizes
- **Sizes**: 64
- **Smallest**: 1/64 — 0.0156 in
- **Largest**: 1 — 1.0000 in
- **Standard**: ANSI/ASME B94.11M; BS 328

## Every Fractional Drill Size

Each size links to its page with the nearest equivalent in the other three series and the threads it taps.

| Drill | Diameter (in) | Diameter (mm) | Fraction | Taps |
| --- | --- | --- | --- | --- |
| [1/64](https://shopmath.org/drills/fractional/1-64.md) | 0.0156 | 0.397 | 1/64 |  |
| [1/32](https://shopmath.org/drills/fractional/1-32.md) | 0.0313 | 0.794 | 1/32 |  |
| [3/64](https://shopmath.org/drills/fractional/3-64.md) | 0.0469 | 1.191 | 3/64 | #0-80 UNF |
| [1/16](https://shopmath.org/drills/fractional/1-16.md) | 0.0625 | 1.587 | 1/16 |  |
| [5/64](https://shopmath.org/drills/fractional/5-64.md) | 0.0781 | 1.984 | 5/64 |  |
| [3/32](https://shopmath.org/drills/fractional/3-32.md) | 0.0938 | 2.381 | 3/32 |  |
| [7/64](https://shopmath.org/drills/fractional/7-64.md) | 0.1094 | 2.778 | 7/64 |  |
| [1/8](https://shopmath.org/drills/fractional/1-8.md) | 0.1250 | 3.175 | 1/8 |  |
| [9/64](https://shopmath.org/drills/fractional/9-64.md) | 0.1406 | 3.572 | 9/64 |  |
| [5/32](https://shopmath.org/drills/fractional/5-32.md) | 0.1563 | 3.969 | 5/32 |  |
| [11/64](https://shopmath.org/drills/fractional/11-64.md) | 0.1719 | 4.366 | 11/64 |  |
| [3/16](https://shopmath.org/drills/fractional/3-16.md) | 0.1875 | 4.763 | 3/16 |  |
| [13/64](https://shopmath.org/drills/fractional/13-64.md) | 0.2031 | 5.159 | 13/64 |  |
| [7/32](https://shopmath.org/drills/fractional/7-32.md) | 0.2188 | 5.556 | 7/32 | 1/4-32 UNEF |
| [15/64](https://shopmath.org/drills/fractional/15-64.md) | 0.2344 | 5.953 | 15/64 |  |
| [1/4](https://shopmath.org/drills/fractional/1-4.md) | 0.2500 | 6.350 | 1/4 |  |
| [17/64](https://shopmath.org/drills/fractional/17-64.md) | 0.2656 | 6.747 | 17/64 |  |
| [9/32](https://shopmath.org/drills/fractional/9-32.md) | 0.2813 | 7.144 | 9/32 | 5/16-32 UNEF |
| [19/64](https://shopmath.org/drills/fractional/19-64.md) | 0.2969 | 7.541 | 19/64 |  |
| [5/16](https://shopmath.org/drills/fractional/5-16.md) | 0.3125 | 7.938 | 5/16 | 3/8-16 UNC |
| [21/64](https://shopmath.org/drills/fractional/21-64.md) | 0.3281 | 8.334 | 21/64 |  |
| [11/32](https://shopmath.org/drills/fractional/11-32.md) | 0.3438 | 8.731 | 11/32 | 3/8-32 UNEF |
| [23/64](https://shopmath.org/drills/fractional/23-64.md) | 0.3594 | 9.128 | 23/64 |  |
| [3/8](https://shopmath.org/drills/fractional/3-8.md) | 0.3750 | 9.525 | 3/8 |  |
| [25/64](https://shopmath.org/drills/fractional/25-64.md) | 0.3906 | 9.922 | 25/64 | 7/16-20 UNF |
| [13/32](https://shopmath.org/drills/fractional/13-32.md) | 0.4063 | 10.319 | 13/32 |  |
| [27/64](https://shopmath.org/drills/fractional/27-64.md) | 0.4219 | 10.716 | 27/64 | 1/2-13 UNC |
| [7/16](https://shopmath.org/drills/fractional/7-16.md) | 0.4375 | 11.113 | 7/16 |  |
| [29/64](https://shopmath.org/drills/fractional/29-64.md) | 0.4531 | 11.509 | 29/64 | 1/2-20 UNF |
| [15/32](https://shopmath.org/drills/fractional/15-32.md) | 0.4688 | 11.906 | 15/32 | 1/2-28 UNEF |
| [31/64](https://shopmath.org/drills/fractional/31-64.md) | 0.4844 | 12.303 | 31/64 | 9/16-12 UNC |
| [1/2](https://shopmath.org/drills/fractional/1-2.md) | 0.5000 | 12.700 | 1/2 |  |
| [33/64](https://shopmath.org/drills/fractional/33-64.md) | 0.5156 | 13.097 | 33/64 | 9/16-24 UNEF, 9/16-18 UNF |
| [17/32](https://shopmath.org/drills/fractional/17-32.md) | 0.5313 | 13.494 | 17/32 | 5/8-11 UNC |
| [35/64](https://shopmath.org/drills/fractional/35-64.md) | 0.5469 | 13.891 | 35/64 |  |
| [9/16](https://shopmath.org/drills/fractional/9-16.md) | 0.5625 | 14.287 | 9/16 |  |
| [37/64](https://shopmath.org/drills/fractional/37-64.md) | 0.5781 | 14.684 | 37/64 | 5/8-24 UNEF, 5/8-18 UNF |
| [19/32](https://shopmath.org/drills/fractional/19-32.md) | 0.5938 | 15.081 | 19/32 |  |
| [39/64](https://shopmath.org/drills/fractional/39-64.md) | 0.6094 | 15.478 | 39/64 |  |
| [5/8](https://shopmath.org/drills/fractional/5-8.md) | 0.6250 | 15.875 | 5/8 |  |
| [41/64](https://shopmath.org/drills/fractional/41-64.md) | 0.6406 | 16.272 | 41/64 | 11/16-24 UNEF |
| [21/32](https://shopmath.org/drills/fractional/21-32.md) | 0.6563 | 16.669 | 21/32 | 3/4-10 UNC |
| [43/64](https://shopmath.org/drills/fractional/43-64.md) | 0.6719 | 17.066 | 43/64 |  |
| [11/16](https://shopmath.org/drills/fractional/11-16.md) | 0.6875 | 17.462 | 11/16 | 3/4-16 UNF |
| [45/64](https://shopmath.org/drills/fractional/45-64.md) | 0.7031 | 17.859 | 45/64 | 3/4-20 UNEF |
| [23/32](https://shopmath.org/drills/fractional/23-32.md) | 0.7188 | 18.256 | 23/32 |  |
| [47/64](https://shopmath.org/drills/fractional/47-64.md) | 0.7344 | 18.653 | 47/64 |  |
| [3/4](https://shopmath.org/drills/fractional/3-4.md) | 0.7500 | 19.050 | 3/4 |  |
| [49/64](https://shopmath.org/drills/fractional/49-64.md) | 0.7656 | 19.447 | 49/64 | 13/16-20 UNEF, 7/8-9 UNC |
| [25/32](https://shopmath.org/drills/fractional/25-32.md) | 0.7813 | 19.844 | 25/32 |  |
| [51/64](https://shopmath.org/drills/fractional/51-64.md) | 0.7969 | 20.241 | 51/64 |  |
| [13/16](https://shopmath.org/drills/fractional/13-16.md) | 0.8125 | 20.637 | 13/16 | 7/8-14 UNF |
| [53/64](https://shopmath.org/drills/fractional/53-64.md) | 0.8281 | 21.034 | 53/64 | 7/8-20 UNEF |
| [27/32](https://shopmath.org/drills/fractional/27-32.md) | 0.8438 | 21.431 | 27/32 |  |
| [55/64](https://shopmath.org/drills/fractional/55-64.md) | 0.8594 | 21.828 | 55/64 |  |
| [7/8](https://shopmath.org/drills/fractional/7-8.md) | 0.8750 | 22.225 | 7/8 | 1-8 UNC |
| [57/64](https://shopmath.org/drills/fractional/57-64.md) | 0.8906 | 22.622 | 57/64 | 15/16-20 UNEF |
| [29/32](https://shopmath.org/drills/fractional/29-32.md) | 0.9063 | 23.019 | 29/32 |  |
| [59/64](https://shopmath.org/drills/fractional/59-64.md) | 0.9219 | 23.416 | 59/64 | 1-12 UNF |
| [15/16](https://shopmath.org/drills/fractional/15-16.md) | 0.9375 | 23.813 | 15/16 |  |
| [61/64](https://shopmath.org/drills/fractional/61-64.md) | 0.9531 | 24.209 | 61/64 | 1-20 UNEF |
| [31/32](https://shopmath.org/drills/fractional/31-32.md) | 0.9688 | 24.606 | 31/32 |  |
| [63/64](https://shopmath.org/drills/fractional/63-64.md) | 0.9844 | 25.003 | 63/64 | 1 1/8-7 UNC |
| [1](https://shopmath.org/drills/fractional/1.md) | 1.0000 | 25.400 | 1 | 1 1/16-18 UNEF, 1 1/8-18 UNEF, 1 1/8-12 UNF, 1 3/16-18 UNEF, 1 1/4-18 UNEF, 1 1/4-12 UNF, 1 1/4-7 UNC, 1 5/16-18 UNEF, 1 3/8-18 UNEF, 1 3/8-12 UNF, 1 3/8-6 UNC, 1 7/16-18 UNEF, 1 1/2-18 UNEF, 1 1/2-12 UNF, 1 1/2-6 UNC, 1 9/16-18 UNEF, 1 5/8-18 UNEF, 1 11/16-18 UNEF, 1 3/4-5 UNC, 2-4 UNC, 2 1/4-4 UNC, 2 1/2-4 UNC, 2 3/4-4 UNC, 3-4 UNC, 3 1/4-4 UNC, 3 1/2-4 UNC, 3 3/4-4 UNC, 4-4 UNC |

_Diameters are nominal. The taps column lists the threads this drill is the recommended tap drill for at the default engagement._

## Sources and Method for the Fractional Drill Series

### Fractional drill sizes

- **Source**: Number/letter: bd_warehouse drill_sizes.csv (Apache-2.0) cross-checked against Wikipedia Drill bit sizes (CC BY-SA 4.0). Fractional: computed 1/64 in steps per ANSI B94.11M. Metric: computed BS 328 increment pattern.
- **Method**: computed
- **Verified against**: Wikipedia Drill bit sizes (CC BY-SA 4.0); 31/31 checks passed

### Assumptions

- Drill diameters are nominal. A worn or run-out drill cuts oversize.
- Dataset scope: Number sizes #61-#80 are stored but tagged demandTier 'extended' — query-space-map.md Appendix A found the tail thinning in the 60s. Sizes below #80 and metric sizes above 25.0 mm excluded.

**Data last verified**: August 1, 2026

## Related pages

- All drill series: [Drill bit size reference](https://shopmath.org/drills.md)
- Every series interleaved by diameter: [Drill size chart](https://shopmath.org/charts/drill-sizes.md)
- Tap drills by thread: [Tap drill chart](https://shopmath.org/charts/tap-drill.md)

---

*Source: [ShopMath](https://shopmath.org/drills/fractional) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*