Clearance Hole Input Form
Plotly Graph
The chart compares the nominal diameter with close, normal, loose, and custom hole recommendations.
Formula Used
Recommended hole diameter = nominal fastener diameter + selected clearance allowance.
Minimum hole diameter = recommended hole diameter − manufacturing tolerance.
Maximum hole diameter = recommended hole diameter + manufacturing tolerance.
Hole area = π × (hole diameter ÷ 2)².
Removed volume = hole area × material thickness × number of holes.
Clearance ratio = diametral clearance ÷ nominal diameter × 100.
How to Use This Calculator
- Enter the nominal diameter of the bolt, screw, or anchor.
- Select millimeters or inches for the input unit.
- Choose close, normal, loose, or custom fit.
- Type a custom allowance if you need a special drill size.
- Add the tolerance, quantity of holes, and material thickness.
- Press the calculate button to show the result block above the form.
- Review the chart, example table, and export buttons for documentation.
Example Data Table
| Nominal Size | Fit | Allowance | Recommended Hole | Tolerance | Hole Range |
|---|---|---|---|---|---|
| 6 mm | Close | 0.20 mm | 6.20 mm | ±0.05 mm | 6.15 to 6.25 mm |
| 10 mm | Normal | 0.50 mm | 10.50 mm | ±0.10 mm | 10.40 to 10.60 mm |
| 16 mm | Loose | 1.00 mm | 17.00 mm | ±0.15 mm | 16.85 to 17.15 mm |
| 0.50 in | Custom | 0.03 in | 0.53 in | ±0.005 in | 0.525 to 0.535 in |
FAQs
1. What is a clearance hole?
A clearance hole is a drilled opening larger than the fastener diameter. It lets a bolt or screw pass through one part without threading into that part.
2. Why is clearance allowance added?
Allowance creates assembly space. It helps account for alignment error, coating thickness, field drilling variation, and easy insertion during construction or fabrication.
3. When should I use a close fit?
Use a close fit when alignment matters and movement must stay minimal. It suits precision brackets, machine bases, templates, and tightly controlled shop work.
4. When is a loose fit better?
Loose fits help with quick field assembly, coatings, galvanizing, thermal expansion, and imperfect alignment. They reduce installation difficulty when precise drilling cannot be guaranteed.
5. Does tolerance change the recommended hole?
Tolerance does not change the target diameter. It defines the acceptable lower and upper manufacturing limits around the recommended drilled size.
6. Can I enter inch values?
Yes. Choose inches in the unit field, then enter nominal diameter, custom allowance, tolerance, and thickness in inches. Results are also shown in millimeters.
7. What does removed volume mean?
Removed volume estimates how much material drilling takes out. It is useful for fabrication review, chip load planning, and rough weight-loss estimation.
8. Can this calculator replace design standards?
No. It is a planning aid. Final hole sizes should still follow project drawings, fastener manufacturer data, fabrication rules, and applicable construction standards.