---
type: "drill"
designation: "13.5 mm"
series: "metric"
series_name: "Metric Drill Sizes"
diameter_in: 0.531496
diameter_mm: 13.5
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/metric/13-5mm
---

# 13.5 mm Drill Bit Size — 0.5315 in / 13.500 mm

A 13.5 mm drill bit is 0.5315 in (13.500 mm) in diameter. It belongs to the metric series of standard twist drills.

- **Designation**: 13.5 mm
- **Series**: Metric
- **Diameter**: 0.5315 in (13.500 mm)

## 13.5 mm Drill Diameter

| Property | Value |
| --- | --- |
| Designation | 13.5 mm |
| Series | Metric |
| Diameter (in) | 0.5315 |
| Diameter (mm) | 13.500 |

## 13.5 mm Drill Equivalents in the Other Size Series

The nearest standard drill to 13.5 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 | -0.3035 in |
| Letter | [Z](https://shopmath.org/drills/letter/z.md) | 0.4130 | 10.490 | -0.1185 in |
| Fractional | [17/32](https://shopmath.org/drills/fractional/17-32.md) | 0.5313 | 13.494 | -0.0002 in |

## Sources and Method for the 13.5 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 13.5 mm Drill Bit

### What size is a 13.5 mm drill bit size?

A 13.5 mm drill bit is 0.5315 in (13.500 mm) in diameter.

### What fraction is a 13.5 mm drill bit?

13.5 mm is 0.5315 in (13.500 mm), which is not itself a fractional size. The closest fractional drill is 17/32 at 0.5313 in (13.494 mm).

## Related pages

- Next size down (any series): [17/32](https://shopmath.org/drills/fractional/17-32.md) — 0.5313 in (13.494 mm)
- Next size up (any series): [13.6 mm](https://shopmath.org/drills/metric/13-6mm.md) — 0.5354 in (13.600 mm)
- Previous in the metric series: [13.4 mm](https://shopmath.org/drills/metric/13-4mm.md)
- Next in the metric series: [13.6 mm](https://shopmath.org/drills/metric/13-6mm.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/13-5mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*