Inch to Millimeter Converter
Enter the value that you want to convert inch (in) to millimeter (mm) or millimeter to inch.Also written as IN to MM conversion.
1 inch = 25.4000000 millimeter
Formula: millimeter = inch value × 25.4000000
IN to MM — inch to millimeter
10 inch = 254.00000 millimeter
Popular Length Converters:
Inch to Millimeter: The Essentials
The Inch Explained
Inch (in) is a unit of length measurement. 1 inch is equal to 25.4000000 millimeter.
The Millimeter Explained
Millimeter (mm) is a unit of length measurement. 1 millimeter is equal to 0.0393701 inch.
Length Conversions in Practice
Length conversions connect the metric system used by most of the world with the imperial system still dominant in the United States, UK construction, and aviation. Architects convert between meters and feet for international projects. Machinists work in thousandths of an inch while referencing metric specifications. Runners compare kilometer race distances to miles. Screen sizes, paper formats, and fabric measurements all require frequent conversion between systems.
inch to millimeter metric conversion table
| 0.01 in | = | 0.25400 mm |
| 0.1 in | = | 2.54000 mm |
| 1 in | = | 25.40000 mm |
| 2 in | = | 50.80000 mm |
| 3 in | = | 76.20000 mm |
| 4 in | = | 101.60000 mm |
| 5 in | = | 127.00000 mm |
| 6 in | = | 152.40000 mm |
| 7 in | = | 177.80000 mm |
| 8 in | = | 203.20000 mm |
| 9 in | = | 228.60000 mm |
| 10 in | = | 254.00000 mm |
| 11 in | = | 279.40000 mm |
| 12 in | = | 304.80000 mm |
| 13 in | = | 330.20000 mm |
| 14 in | = | 355.60000 mm |
| 15 in | = | 381.00000 mm |
| 16 in | = | 406.40000 mm |
| 17 in | = | 431.80000 mm |
| 18 in | = | 457.20000 mm |
| 19 in | = | 482.60000 mm |
| 20 in | = | 508.00000 mm |
| 30 in | = | 762.00000 mm |
| 40 in | = | 1016.00000 mm |
| 50 in | = | 1270.00000 mm |
| 60 in | = | 1524.00000 mm |
| 70 in | = | 1778.00000 mm |
| 80 in | = | 2032.00000 mm |
| 90 in | = | 2286.00000 mm |
| 100 in | = | 2540.00000 mm |
| 200 in | = | 5080.00000 mm |
| 300 in | = | 7620.00000 mm |
| 400 in | = | 10160.00000 mm |
| 500 in | = | 12700.00000 mm |
| 600 in | = | 15240.00000 mm |
| 700 in | = | 17780.00000 mm |
| 800 in | = | 20320.00000 mm |
| 900 in | = | 22860.00000 mm |
| 1000 in | = | 25400.00000 mm |
How to Convert IN to MM (Inch to Millimeter)?
We can convert inch to millimeter by using an example.
Example:
Convert 20 Inch to Millimeter?
We know 1 Inch = 25.4000000 millimeter; 1 Millimeter = 0.0393701 inch.
20 inch = ___mm
20 × 25.4000000 = 508.00000 mm (we know 1 inch = 25.4000000 millimeter)
Answer:
20 inch = 508.00000 millimeter
How to Convert Inches to Millimeters (Step-by-Step)
Converting inches to millimeters is essential in machining, precision engineering, and CNC programming where metric specifications are required. Multiply inches by 25.4 to get millimeters.
- Write down the measurement in inches (convert fractions to decimals if needed).
- Multiply the inch value by 25.4.
- The result is the equivalent length in millimeters.
- For fractional inches: first divide numerator by denominator, then multiply by 25.4.
Common Inch to Millimeter Conversions
Reference table of fractional and decimal inches converted to millimeters for machining and precision work.
| Inch | Millimeter |
|---|---|
| 1/16 inch | 1.588 mm |
| 1/8 inch | 3.175 mm |
| 1/4 inch | 6.35 mm |
| 3/8 inch | 9.525 mm |
| 1/2 inch | 12.7 mm |
| 3/4 inch | 19.05 mm |
| 1 inch | 25.4 mm |
| 2 inches | 50.8 mm |
Solved Examples: Inches to mm
Question 1: A CNC program specifies a pocket depth of 0.375 inches. Convert to mm.
Solution:
mm = inches × 25.4
= 0.375 × 25.4
= 9.525 mm
Answer: 0.375 inches = 9.525 mm (3/8 inch pocket depth)
Question 2: Convert 5/32 inch drill bit diameter to millimeters.
Solution:
First convert fraction: 5/32 = 0.15625 inches
mm = 0.15625 × 25.4
= 3.969 mm
Answer: 5/32 inch = 3.969 mm (closest metric drill: 4 mm)
Question 3: A bearing has a 1.375-inch bore. What is this in mm?
Solution:
mm = 1.375 × 25.4
= 34.925 mm
≈ 35 mm standard bearing bore
Answer: 1.375 inches = 34.925 mm (standard 35 mm bearing)
Question 4: Sheet metal is 0.032 inches thick. Convert to mm.
Solution:
mm = 0.032 × 25.4
= 0.8128 mm
≈ 0.8 mm sheet metal gauge
Answer: 0.032 inches = 0.813 mm (20-gauge sheet metal)
Practice Questions
Try solving these on your own to test your understanding:
- Convert 7/16 inch to mm. (Answer: 11.1125 mm)
- A shaft diameter is 0.750 inches. What is this in mm? (Answer: 19.05 mm)
- Convert 2.5 inches to mm. (Answer: 63.5 mm)
- A 9/64 inch drill bit equals how many mm? (Answer: 3.572 mm)
- Convert 0.001 inch (1 thou) to mm. (Answer: 0.0254 mm)
CNC Programming: Converting Imperial Drawings to Metric
When programming CNC machines in metric mode (G21) from imperial drawings, every dimension must be converted by multiplying by 25.4. Common pitfalls: forgetting to convert feed rates (IPM to mm/min: multiply by 25.4), tool diameters, and depth increments. A 0.001" tolerance becomes 0.0254 mm — often rounded to 0.025 mm in metric. Modern CAM software handles this automatically, but manual verification prevents crashes and scrap parts.
Fractional Inch Drill Bit Chart
US drill bits are sold in 1/64" increments. Key sizes and metric equivalents: 1/64" = 0.397 mm, 1/32" = 0.794 mm, 1/16" = 1.588 mm, 3/32" = 2.381 mm, 1/8" = 3.175 mm, 5/32" = 3.969 mm, 3/16" = 4.763 mm, 7/32" = 5.556 mm, 1/4" = 6.35 mm, 5/16" = 7.938 mm, 3/8" = 9.525 mm, 7/16" = 11.113 mm, 1/2" = 12.7 mm. When a specific metric size is needed, use numbered or lettered drill bits for closer matches.
Precision Measurement: Thou, Mils, and Millimeters
In precision engineering, "thou" (thousandths of an inch) is the everyday unit in imperial shops. 1 thou = 0.001 inch = 0.0254 mm = 25.4 micrometers. Common conversions: 0.5 thou = 12.7 μm (mirror finish), 1 thou = 25.4 μm (precision grinding), 2 thou = 50.8 μm (standard machining), 5 thou = 127 μm (rough machining), 10 thou = 254 μm (sheet metal tolerance). Understanding both systems is mandatory when working with international suppliers.
Key Takeaways
- Multiply inches by 25.4 to get millimeters (exact conversion).
- Convert fractional inches to decimals first: 3/8" = 0.375" = 9.525 mm.
- 1 thou (0.001") = 0.0254 mm — the bridge between imperial and metric precision.
- CNC programs in G21 (metric) need all dimensions × 25.4 from imperial drawings.
- Standard metric drill bits rarely match imperial fractions exactly.
- Memorize 1/4" = 6.35 mm and 1/2" = 12.7 mm as quick reference anchors.
Inch to Millimeter Conversion Formula
millimeter = inch × 25.4000000
1 inch = 25.4000000 millimeter
1 millimeter = 0.0393701 inch
Reverse: inch = millimeter × 0.0393701
Frequently Asked Questions
How many millimeter are in 1 inch?
There are 25.4000000 millimeter in 1 inch. To convert inch to millimeter, multiply the value by 25.4000000.
How do I convert inch to millimeter?
Multiply your inch value by 25.4000000 to get the equivalent in millimeter. For example, 5 inch = 5 × 25.4000000 = 127.00000 millimeter.
How do I convert millimeter to inch?
Multiply your millimeter value by 0.0393701 to get the equivalent in inch. Alternatively, divide by 25.4000000.
What is 10 inch in millimeter?
10 inch is equal to 254.00000 millimeter.
What is 100 inch in millimeter?
100 inch is equal to 2540.00000 millimeter.