Exact inch to millimeter reference

1/4 inch to mm: 6.3500 mm

Convert 1/4 inch to millimeters for CNC setup sheets, drawings, inspection notes, and supplier communication. The formula uses the exact international inch standard.

Answer first

1/4 inch =

6.3500 mm

2 decimals: 6.35
3 decimals: 6.350
4 decimals: 6.3500

Formula and precision policy

mm = inch × 25.4 → 0.25 × 25.4 = 6.3500 mm

The exact conversion uses 1 inch = 25.4 mm. This page displays 6.3500 mm by default. For CNC, inspection, RFQ, or supplier documents, keep the precision required by the drawing, tolerance block, process plan, or inspection equipment.

Equivalent forms

1/4 inch = 0.25 inch
0.25 inch × 25.4 = 6.3500 mm
6.35 mm rounded to 2 decimals; 6.350 mm rounded to 3 decimals

Nearby inch to mm values

Value	Decimal inch	Millimeters	Reference
3/16 inch	0.1875	4.7625 mm	Open page
5/16 inch	0.3125	7.9375 mm	Open page
1/8 inch	0.125	3.1750 mm	Open page
3/8 inch	0.375	9.5250 mm	Open page
1/16 inch	0.0625	1.5875 mm	Open page
7/16 inch	0.4375	11.1125 mm	Open page

Manufacturing context and caveat

A 1/4 inch dimension can describe thickness, spacing, or nominal hardware context. Do not infer thread, drill, or fastener interchangeability from the conversion alone.

Reference-only caveat: this conversion does not certify tolerance, fit, pressure, load, code compliance, material equivalence, or interchangeability. Confirm the controlling drawing, standard, supplier data, and engineering approval before manufacturing.

FAQs

How many millimeters is 1/4 inch?

1/4 inch equals 6.3500 mm using the exact conversion factor 1 inch = 25.4 mm.

What formula converts 1/4 inch to mm?

Use mm = inch × 25.4. For this page, 0.25 × 25.4 = 6.3500 mm.

Should I round 6.3500 mm for CNC or inspection work?

Use the precision required by the drawing, process plan, or inspection method. This page shows 6.35 mm, 6.350 mm, and 6.3500 mm so you can choose the appropriate display precision.

Is 1/4 inch the same as 0.25 inch?

Yes. 1/4 inch is represented here as 0.25 inch before multiplying by 25.4 to get millimeters.

Can this conversion decide fit, tolerance, or replacement parts?

No. This is a reference unit conversion only. Confirm drawing tolerances, standards, material specifications, supplier certificates, and engineering approval before manufacturing or substituting parts.