---
type: "drill"
designation: "12.3 mm"
series: "metric"
series_name: "Metric Drill Sizes"
diameter_in: 0.484252
diameter_mm: 12.3
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/metric/12-3mm
---

# 12.3 mm Drill Bit Size — 0.4843 in / 12.300 mm

A 12.3 mm drill bit is 0.4843 in (12.300 mm) in diameter. It belongs to the metric series of standard twist drills.

- **Designation**: 12.3 mm
- **Series**: Metric
- **Diameter**: 0.4843 in (12.300 mm)

## 12.3 mm Drill Diameter

| Property | Value |
| --- | --- |
| Designation | 12.3 mm |
| Series | Metric |
| Diameter (in) | 0.4843 |
| Diameter (mm) | 12.300 |

## 12.3 mm Drill Equivalents in the Other Size Series

The nearest standard drill to 12.3 mm 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 | -0.2563 in |
| Letter | [Z](https://shopmath.org/drills/letter/z.md) | 0.4130 | 10.490 | -0.0713 in |
| Fractional | [31/64](https://shopmath.org/drills/fractional/31-64.md) | 0.4844 | 12.303 | +0.0001 in |

## Sources and Method for the 12.3 mm 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 12.3 mm Drill Bit

### What size is a 12.3 mm drill bit size?

A 12.3 mm drill bit is 0.4843 in (12.300 mm) in diameter.

### What fraction is a 12.3 mm drill bit?

12.3 mm is 0.4843 in (12.300 mm), which is not itself a fractional size. The closest fractional drill is 31/64 at 0.4844 in (12.303 mm).

## Related pages

- Next size down (any series): [12.2 mm](https://shopmath.org/drills/metric/12-2mm.md) — 0.4803 in (12.200 mm)
- Next size up (any series): [31/64](https://shopmath.org/drills/fractional/31-64.md) — 0.4844 in (12.303 mm)
- Previous in the metric series: [12.2 mm](https://shopmath.org/drills/metric/12-2mm.md)
- Next in the metric series: [12.4 mm](https://shopmath.org/drills/metric/12-4mm.md)
- All metric sizes: [Metric drill sizes](https://shopmath.org/drills/metric.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/metric/12-3mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*