How do I convert thou (mils) to millimeters?

Multiply thou by 0.0254 to get millimeters. Formula: mm = thou x 0.0254. Examples: 1 thou = 0.0254 mm, 10 thou = 0.254 mm, 100 thou = 2.54 mm (= 0.1 inch), 1000 thou = 25.4 mm (= 1 inch).

What is 10 thou in mm?

10 thou = 10 x 0.0254 = 0.254 mm. This is a very small measurement commonly used in precision engineering. A human hair is about 40-100 thou thick.

Why are thou measurements used in engineering?

Thou (mils) are used in engineering because they allow whole-number expression of small dimensions without decimals. Saying a gap is 5 thou is cleaner than 0.127 mm or 0.005 inches. It is standard in US machining, electronics (PCB trace widths), and wire gauges.

What is 0.001 inch in mm?

0.001 inch = 1 thou = 0.0254 mm. This is a common precision machining tolerance. CNC machines can routinely hold tolerances of 0.001-0.002 inch (0.025-0.051 mm).

Thou (Mils) to Millimeters Converter

Thou (Mils) to Millimeters Calculator

Thou (Mils)

thou

to Millimeters

How to Convert Thou (Mils) to Millimeters

Thou (or mil) is commonly used in engineering and manufacturing to measure small thicknesses. One thou equals 0.0254 millimeters.

The Mathematical Formula

To convert thou to millimeters multiply the value by 0.0254:


                                                Millimeters = Thou × 0.0254

Thou to Millimeters Table

Thou (mil)	Millimeters (mm)
1 mil	0.0254 mm
10 mil	0.254 mm
25 mil	0.635 mm
100 mil	2.54 mm

Thou (Mils) to Millimetres

One thou (thousandth of an inch, also called a mil) equals exactly 0.0254 mm. To convert thou to mm, multiply by 0.0254; to convert mm to thou, divide by 0.0254 (or multiply by 39.3701). This unit is used in precision engineering, machining tolerances, PCB trace widths, and film thickness. A human hair is 50–100 thou (1.27–2.54 mm); a sheet of aluminium kitchen foil is approximately 0.6 thou (0.015 mm).

Machining tolerances for precision parts are often specified in thou: a tolerance of ±1 thou (±0.025 mm) is achievable with good CNC machinery; ±0.1 thou (±0.0025 mm) requires precision grinding. Spring wire diameters are catalogued in thou and AWG (American Wire Gauge). PCB design tools in the US still default to mils (thou) for trace width, clearance, and via hole specifications, while IPC standards increasingly use millimetres.

Thou (mils)	mm	Common Application
0.4	0.0102	Precision film coating
1	0.0254	Tight machining tolerance
4	0.1016	Standard paper thickness
10	0.254	Precision drill diameter step
25	0.635	Thin PCB trace
100	2.540	One-tenth of an inch
1000	25.400	One inch

Thou (mils)

Common Application

0.4

0.0102

Precision film coating

0.0254

Tight machining tolerance

0.1016

Standard paper thickness

0.254

Precision drill diameter step

0.635

Thin PCB trace

100

2.540

One-tenth of an inch

1000

25.400

One inch

Converting Thousandths of an Inch to Millimeters

One thou (0.001 inch) equals exactly 0.0254 mm. Converting thou to millimeters: multiply by 0.0254. Reverse: divide mm by 0.0254. Engineers working with mixed US and metric specifications — common in automotive and aerospace supply chains — need this conversion constantly. A 5-thou gap (typical shim selection in engines) equals 0.127 mm. A 10-thou wall thickness in a sheet metal part equals 0.254 mm. High-precision CNC work specifies tolerances in thou because US machine tools and measuring instruments read in thou natively, but export technical drawings often use mm. Powder-coat and paint specifications quote film thickness in thou; European and Asian painters use micrometers (1 μm = 0.03937 thou). Sheet metal gauges are another area: 18 AWG steel sheet is 0.048 inches (48 thou = 1.219 mm), and knowing the thou-to-mm conversion helps when ordering material from metric suppliers.

Thou	mm	Context
1	0.0254	Fine tolerance
5	0.127	Engine shim
10	0.254	PCB trace
50	1.270	Sheet metal
1000	25.40	One inch

Thou

Context

0.0254

Fine tolerance

0.127

Engine shim

0.254

PCB trace

1.270

Sheet metal

1000

25.40

One inch

Thou (Mils) to Millimeters Calculator

How to Convert Thou (Mils) to Millimeters

The Mathematical Formula

Thou to Millimeters Table

Thou (Mils) to Millimetres

Thou to Millimetres Reference

Converting Thousandths of an Inch to Millimeters

Thousandths (Thou) to Millimeters Reference Table

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