Clearance Hole Calculator

Advanced tool for calculating clearance hole sizes with selectable fit categories close normal and loose supports metric and imperial inputs auto applies smart tolerances provides visual guidance lets you add rows edit values and download results as CSV or generate a polished PDF ready for shop floor use with helpful notes and example data

Inputs

Unit System *

Nominal Fastener Size *

Diameter of the bolt/screw (not the pitch).

Fit Class *

Hole Count For batch planning and material estimates.

Optional Extra Allowance

Accounts for coating, misalignment, or jig tolerances.

Close ≈ small clearance Normal ≈ general purpose Loose ≈ assembly friendly

Results

#	Units	Nominal Size	Fit	Base Allowance k	Extra Allowance	Recommended Hole	Count	Notes	Action

Formula used

We estimate the clearance hole diameter as:

d_clearance = d_nominal + k_fit(d_nominal) + extra

where k_fit is an empirically chosen allowance that scales with the nominal fastener size and the required fit. These heuristics are practical shop rules and do not replace standards.

Metric (mm):
- Close: k = 0.15 + 0.01·d
- Normal: k = 0.30 + 0.02·d
- Loose: k = 0.60 + 0.03·d
Imperial (in):
- Close: k = 0.004 + 0.001·d
- Normal: k = 0.008 + 0.002·d
- Loose: k = 0.015 + 0.003·d

Round up to available drill sizes as needed. For mission‑critical designs, consult ISO 273 or ASME guidance.

Example data

Units	Nominal	Fit	Extra	Count
mm	3	close	0	4
mm	6	normal	0.1	8
mm	12	loose	0.2	6
in	0.25	close	0	10
in	0.5	normal	0.005	12
in	0.75	loose	0.01	2

Click “Load Example Data” then export as CSV or PDF.

Inputs

Results

Formula used

Example data

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