---
type: "drill"
designation: "3/8"
series: "fractional"
series_name: "Fractional Drill Sizes"
diameter_in: 0.375
diameter_mm: 9.525
fraction_label: "3/8"
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/fractional/3-8
---

# 3/8 Drill Bit Size — 0.3750 in / 9.525 mm

A 3/8 drill bit is 0.3750 in (9.525 mm) in diameter. It belongs to the fractional series of standard twist drills.

- **Designation**: 3/8
- **Series**: Fractional
- **Diameter**: 0.3750 in (9.525 mm)
- **Fraction**: 3/8

## 3/8 Drill Diameter

| Property | Value |
| --- | --- |
| Designation | 3/8 |
| Series | Fractional |
| Diameter (in) | 0.3750 |
| Diameter (mm) | 9.525 |
| Fractional call-out | 3/8 |

## 3/8 Drill Equivalents in the Other Size Series

The nearest standard drill to 3/8 in each of the other three series. Nothing here is an exact match unless the difference column reads 0.0000 in.

| Series | Nearest drill | Diameter (in) | Diameter (mm) | Difference |
| --- | --- | --- | --- | --- |
| Number | [#1](https://shopmath.org/drills/number/1.md) | 0.2280 | 5.791 | -0.1470 in |
| Letter | [V](https://shopmath.org/drills/letter/v.md) | 0.3770 | 9.576 | +0.0020 in |
| Metric | [9.5 mm](https://shopmath.org/drills/metric/9-5mm.md) | 0.3740 | 9.500 | -0.0010 in |

## Sources and Method for the 3/8 Drill Size

### Drill index

- **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; measure the hole, not the shank, when the fit matters.
- 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

## Common Questions About the 3/8 Drill Bit

### What size is a 3/8 drill bit size?

A 3/8 drill bit is 0.3750 in (9.525 mm) in diameter. The nearest fractional call-out is 3/8.

### What is the metric equivalent of a 3/8 drill bit?

The closest metric drill to 3/8 (0.3750 in (9.525 mm)) is 9.5 mm at 0.3740 in (9.500 mm) — a difference of 0.0010 in.

## Related pages

- Next size down (any series): [9.5 mm](https://shopmath.org/drills/metric/9-5mm.md) — 0.3740 in (9.500 mm)
- Next size up (any series): [V](https://shopmath.org/drills/letter/v.md) — 0.3770 in (9.576 mm)
- Previous in the fractional series: [23/64](https://shopmath.org/drills/fractional/23-64.md)
- Next in the fractional series: [25/64](https://shopmath.org/drills/fractional/25-64.md)
- All fractional sizes: [Fractional drill sizes](https://shopmath.org/drills/fractional.md)
- All drill sizes: [Drill bit size reference](https://shopmath.org/drills.md)
- Complete index 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/3-8) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*