# Clearance Hole Calculator

URL: https://speedycalculator.com/calculators/construction/clearance-hole/
Last updated: 2026-10-25

> The clearance hole calculator gives the close, normal and loose fit clearance hole diameters for metric bolts (ISO 273) and inch bolts and screws (ASME B18.2.8), in millimetres and inches with the nearest fraction.

## Inputs

- System
- Metric size
- Inch size
- Fit

## Results

- Clearance hole diameter
- Nearest fraction

## Formula

```
Hole diameter from ISO 273 (metric) or ASME B18.2.8 (inch) tables for the chosen fit
```

## Explanation

A clearance hole lets a bolt or screw pass through a part without engaging threads. Close-fit holes locate parts accurately, normal fit is the default for general assembly, and loose fit allows for misalignment between several parts. Standards list the diameters so parts made in different shops fit together.

### How to use the Clearance Hole Calculator

- **System**
- **Metric size**
- **Inch size**
- **Fit**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Choose metric or inch, the fastener size and the fit class. The calculator looks up the hole diameter from the standard table.

### Metric clearance holes (ISO 273, mm)

SizeCloseNormalLooseM1.61.71.82M22.22.42.6M2.52.72.93.1M33.23.43.6M44.34.54.8M55.35.55.8M66.46.67M88.4910M1010.51112M121313.514.5M141515.516.5M161717.518.5M20212224M24252628M30313335M36373942

### Inch clearance holes (in)

SizeCloseNormalLoose#20.0940.0960.106#40.1160.1250.141#60.1440.1560.172#80.1770.1880.203#100.2010.2190.234¼0.2660.2810.2975/160.3280.3440.359⅜0.3910.4060.4227/160.4530.4690.484½0.5160.5310.562⅝0.6560.6880.719¾0.7810.8120.844⅞0.9060.9380.96911.0311.0621.094

### Tips for an accurate estimate

- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer's coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.

### Common mistakes to avoid

- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.

### Inputs explained

FieldWhat to enterSystemChoose one: Metric (ISO 273), Inch (ASME B18.2.8)Metric sizeChoose one: M1.6, M2, M2.5, M3 …Inch sizeChoose one: #2, #4, #6, #8 …FitChoose one: Close, Normal, Loose

## Worked example

Inputs — System: Metric (ISO 273); Metric size: M6; Inch size: ¼; Fit: Normal.

Results — **Clearance hole diameter = 6.6 mm**; Nearest fraction = 17/64.

## FAQ

**What clearance hole for an M6 bolt?**
6.4 mm close, 6.6 mm normal and 7.0 mm loose fit (ISO 273).

**What clearance hole for a ¼ in bolt?**
0.266 in (H drill) close, 0.281 in (9/32) normal and 0.297 in (19/64) loose.

**Why not just drill the bolt size?**
Without clearance the bolt binds; small differences in hole position then make assembly impossible.

**What formula does the Clearance Hole Calculator use?**
Hole diameter from ISO 273 (metric) or ASME B18.2.8 (inch) tables for the chosen fit.


## Sources

- [ISO 273 – Fasteners: clearance holes for bolts and screws](https://www.iso.org/standard/4170.html)