Exact inch to millimeter reference

1/8 inch to mm: 3.1750 mm

Convert 1/8 inch to millimeters for CNC setup sheets, drawings, inspection notes, and supplier communication. The formula uses the exact international inch standard.

Answer first

1/8 inch =

3.1750 mm

2 decimals: 3.17
3 decimals: 3.175
4 decimals: 3.1750

Formula and precision policy

mm = inch × 25.4 → 0.125 × 25.4 = 3.1750 mm

The exact conversion uses 1 inch = 25.4 mm. This page displays 3.1750 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

1/8 inch = 0.125 inch
0.125 inch × 25.4 = 3.1750 mm
3.17 mm rounded to 2 decimals; 3.175 mm rounded to 3 decimals

Nearby inch to mm values

Value	Decimal inch	Millimeters	Reference
1/16 inch	0.0625	1.5875 mm	Open page
3/16 inch	0.1875	4.7625 mm	Open page
1/4 inch	0.25	6.3500 mm	Open page
5/16 inch	0.3125	7.9375 mm	Open page
3/8 inch	0.375	9.5250 mm	Open page
7/16 inch	0.4375	11.1125 mm	Open page

Manufacturing context and caveat

A 1/8 inch value appears in stock, drill, wrench, and spacing references. Treat the converted millimeter value as a base dimension only.

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 1/8 inch?

1/8 inch equals 3.1750 mm using the exact conversion factor 1 inch = 25.4 mm.

What formula converts 1/8 inch to mm?

Use mm = inch × 25.4. For this page, 0.125 × 25.4 = 3.1750 mm.

Should I round 3.1750 mm for CNC or inspection work?

Use the precision required by the drawing, process plan, or inspection method. This page shows 3.17 mm, 3.175 mm, and 3.1750 mm so you can choose the appropriate display precision.

Is 1/8 inch the same as 0.125 inch?

Yes. 1/8 inch is represented here as 0.125 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.