Millimeters to Inches Converter

Convert millimeters to inches instantly with our free online tool. Essential for engineering, drill bits, and 3D printing.

Length Converter

1 mm = 0.0393700787 in

The quick answer for 1 Millimeters — type any value below for the exact result

Enter Millimeters

Millimeters

Result in Inches

Inches

mm to in Conversion Formula

To convert millimeters to inches, divide the millimeter value by 25.4. This works because one inch is defined as exactly 25.4 millimeters, so 1 mm = 0.03937 in.

1 mm = 0.0393700787 in

Millimeters and Inches Explained

Millimeters (mm)

The millimeter is a metric unit of length equal to one thousandth of a meter — about 0.039 inches, roughly the thickness of a credit card (0.76 mm) or a grain of rice width. It is the default unit on technical drawings, machining tolerances, drill bits, bolts, and calipers worldwide. Because it is small enough for precise work yet easy to scale up (1,000 mm = 1 m), it anchors most engineering measurement in metric countries.

Where it is used: Used worldwide in machining, construction fasteners, medicine (tumor sizes), photography (film and filters), and rainfall records.

Origin: Created with the metric system in 1795 from the Latin "mille" for thousand; it became the workhorse unit of industrial measurement during the 19th century.

Inches (in)

The inch is a US customary and imperial unit of length equal to exactly 25.4 millimeters, or one twelfth of a foot. It is the standard unit for screen diagonals, pipe threads, lumber, and wrench sizes in the United States. In machine-shop practice it is often divided into 1/64-inch increments or expressed as thousandths ("thou"), so 0.5 in reads as 500 thou — a habit that makes metric-inch conversion a daily necessity.

Where it is used: Dominant in US manufacturing, plumbing, and carpentry, and used internationally for display sizes and some aviation dimensions.

Origin: Derived from the Roman "uncia" (one twelfth), traditionally the width of a thumb; fixed at exactly 2.54 cm by the 1959 international yard and pound agreement.

Millimeters to Inches Conversion Table

Millimeters (mm)	Inches (in)
0.5 mm	0.0196850394 in
1 mm	0.0393700787 in
1.5 mm	0.0590551181 in
2 mm	0.0787401575 in
2.5 mm	0.0984251969 in
3 mm	0.1181102362 in
4 mm	0.157480315 in
5 mm	0.1968503937 in
6 mm	0.2362204724 in
8 mm	0.3149606299 in
10 mm	0.3937007874 in
12 mm	0.4724409449 in
15 mm	0.5905511811 in
20 mm	0.7874015748 in
25 mm	0.9842519685 in
50 mm	1.968503937 in
100 mm	3.937007874 in

Inches to Millimeters Conversion Table

Inches (in)	Millimeters (mm)
0.0625 in	1.5875 mm
0.125 in	3.175 mm
0.25 in	6.35 mm
0.5 in	12.7 mm
0.75 in	19.05 mm
1 in	25.4 mm
2 in	50.8 mm
4 in	101.6 mm
8 in	203.2 mm
12 in	304.8 mm
16 in	406.4 mm

Millimeters to Inches in Everyday Objects

Common real-world examples that make Millimeters and Inches easy to picture at a glance.

	Millimeters (mm)	Inches (in)
A credit card thickness	0.76 mm	0.0299212598 in
A pencil lead diameter	0.7 mm	0.0275590551 in
A CD disc thickness	1.2 mm	0.0472440945 in
A grain of rice	6 mm	0.2362204724 in
An M8 bolt diameter	8 mm	0.3149606299 in
A US dime diameter	17.91 mm	0.7051181102 in

When You Need Millimeters to Inches Conversions

Tire Tread Depth Checks

Tread gauges sold in Europe read millimeters while US charts use 32nds of an inch. Converting the 4 mm warning level to 0.157 in (about 5/32 in) tells you whether the tires survive another season.

3D Printer Layer Heights

Slicer profiles mix a 0.4 mm nozzle with layer heights quoted in inches on US forums. A 0.2 mm layer converts to 0.00787 in, which fits the "about 8 thou" advice threads give for first-layer calibration.

Matching Drill Bits to Bolts

A metric clearance hole for an M6 bolt is 6.5 mm. The imperial bit box starts at 1/4 in, so converting 6.5 mm to 0.2559 in confirms the 1/4 bit (6.35 mm) is a touch tight and a letter-size F bit fits better.

Machining Tolerances on Mixed Drawings

A shaft journal specified at 19.05 mm ±0.05 mm must mate with a bearing bore drawn in inches. Converting 19.05 mm to exactly 0.75 in keeps the press fit inside the 0.002 in tolerance band the customer expects.

Related Length Conversions

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Feet to Meters Converter

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Kilometers to Miles Converter

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Miles to Kilometers Converter

Miles → Kilometers

Yards to Meters Converter

Yards → Meters

Meters to Yards Converter

Meters → Yards

Feet to Inches Converter

Feet → Inches

Kilometers to Meters Converter

Kilometers → Meters

Meters to Kilometers Converter

Meters → Kilometers

Nautical Miles to Kilometers Converter

Nautical Miles → Kilometers

Micrometers to Millimeters Converter

Micrometers → Millimeters

Decimeters to Centimeters Converter

Decimeters → Centimeters

How to Use

1

Enter the Millimeter Value

Type the dimension in millimeters — for example, enter 16 for a 16 mm lug bolt on a European car
2

See the Inch Result

The equivalent appears instantly: 16 mm = 0.62992 in, so you reach for a 5/8-inch socket (0.625 in)
3

Copy or Swap

Copy the result to your clipboard or click Swap to convert inches back to millimeters
4

Use the Conversion Table

Check the table for common values like 6 mm = 0.23622 in or 25 mm = 0.98425 in

Why Use Be Converter?

Instant Precision Conversion

Get exact millimeter to inch results in real-time as you type — ideal at the drill press or lathe

Machining-Grade Accuracy

Uses the exact standard of 25.4 mm per inch, so an M8 bolt shank converts to 0.31496 in with full precision

Workshop Reference Table

Common metric sizes at a glance — from a 2 mm drill bit to a 50 mm camera filter thread

Swap with One Click

Toggle between mm and in instantly — essential when matching metric parts to imperial tooling

Free & Unlimited

No signup, no limits. Convert as many dimensions as your project needs — always free

Completely Private

All calculations run locally in your browser. Your engineering drawings never leave your device

Frequently Asked Questions

How many inches are in 1 millimeter?

1 millimeter equals 0.03937 inches. This comes directly from the definition of 1 inch as exactly 25.4 mm — one millimeter is therefore 1/25.4 of an inch.

How do I convert mm to inches manually?

Divide the millimeter value by 25.4. For example, a 12 mm wrench target is 12 ÷ 25.4 = 0.47244 in. A quick estimate: divide mm by 25 — 12 ÷ 25 = 0.48 in, within 2% of the exact answer.

What is 10 mm in inches?

10 millimeters equals 0.3937 inches — just under 4/10 of an inch. This is a common size for jewelry, sensor stacks, and standoffs, and it sits between the 3/8 in (9.525 mm) and 7/16 in (11.1125 mm) imperial marks.

How many mm is a 1/4 inch drill bit?

A 1/4 inch bit is 6.35 mm exactly. Other common equivalences: 1/8 in = 3.175 mm, 1/2 in = 12.7 mm, and 3/4 in = 19.05 mm. Metric bit sets skip these values, so conversion is routine in mixed workshops.

What is 6 mm in inches for wrench sizes?

6 mm equals 0.23622 in, which is just under 1/4 inch (0.25 in). In practice a 6 mm fastener needs a 6 mm socket — the nearest imperial size, 1/4 in, is loose enough to round off the hex corners.

What is 100 mm in inches?

100 millimeters equals 3.937 in — almost exactly 4 inches (101.6 mm). Cabinet makers use this shortcut constantly: think "25 mm per inch" and you are within 1.6% of the exact 25.4 factor.

Is 5 mm bigger than 1/4 inch?

No. 5 mm converts to 0.19685 in, which is smaller than 0.25 in (6.35 mm). The crossing point matters in tire tread depth gauges: the UK legal limit of 1.6 mm is about 2/32 in, while a new tire starts near 8 mm (10/32 in).

Why do engineers prefer millimeters over inches?

Metric drawings in millimeters avoid fractional and decimal-inch mixing — 1/64 in increments force awkward numbers like 0.396875 mm. Millimeters also scale cleanly with micrometers (0.001 mm) and meters (1,000 mm), which keeps tolerances, sheet-metal gauges, and CAD units consistent.

About Millimeters to Inches Converter

Our free online millimeters to inches converter provides instant, precise small-dimension conversions for engineering, machining, and DIY work. Whether you are matching a metric bolt to an imperial socket, sizing drill bits, reading a European parts catalog, checking tire tread depth, or setting up a 3D printer, this tool delivers reliable results. Millimeters dominate technical drawings worldwide, while inches remain common in US workshops, so this conversion bridges the two systems at the precision where it matters most.

Expert Tips for mm to in Conversion

The exact factor is 1 mm = 0.0393701 in, because 1 inch is defined as exactly 25.4 mm. Dividing by 25.4 always gives the exact answer — never round before the final step.

Memorize socket landmarks: 8 mm = 0.31496 in, 10 mm = 0.3937 in, 13 mm = 0.51181 in (close to 1/2 in), and 17 mm = 0.66929 in. These cover most automotive fasteners.

For 3D printing, a standard 0.4 mm nozzle extrudes layers from 0.1 to 0.32 mm — that is 0.00394 to 0.0126 in. Slicers mix units, so keep the 25.4 factor handy.

Tire tread: new passenger tires start near 8 mm (0.315 in) and the common replacement threshold is 3 mm (0.118 in). US gauges marked in 32nds need 4/32 in ≈ 3.2 mm.

Printed circuit board work jumps between units constantly: a 1.6 mm standard board is 0.06299 in, and 2.54 mm pin pitch equals exactly 0.1 in — the classic DIP spacing.