MM to Inches Converter
Convert millimeters to inches and vice versa with instant, accurate results
Convert Length Units
Enter value in millimeters
Result in inches
Conversion Results
Common MM to Inches Conversions
| Millimeters (mm) | Inches (decimal) | Inches (fraction) |
|---|---|---|
| 1 mm | 0.0394" | ~1/25" |
| 5 mm | 0.1969" | ~13/64" |
| 10 mm | 0.3937" | ~25/64" |
| 25 mm | 0.9843" | ~63/64" |
| 25.4 mm | 1.0000" | 1" |
| 50 mm | 1.9685" | ~2" |
| 100 mm | 3.9370" | ~4" |
| 254 mm | 10.0000" | 10" |
| 500 mm | 19.6850" | ~19 11/16" |
| 1000 mm | 39.3701" | ~39 3/8" |
Quick Reference
Metric System
Millimeter (mm)
1/1000 of a meter
Imperial System
Inch (in)
1/12 of a foot
Conversion Factor
1 inch = 25.4 mm
Exact conversion
Conversion Tips
Use fractional inches for woodworking and construction
Decimal inches work best for engineering drawings
Millimeters provide more precision for small measurements
Always double-check conversions for critical applications
Understanding MM to Inches Conversion
What is a Millimeter?
A millimeter (mm) is a unit of length in the metric system, equal to one-thousandth of a meter. It's commonly used for precise measurements in engineering, manufacturing, and science.
Common Uses of Millimeters
- •Engineering drawings and technical specifications
- •Manufacturing and machining tolerances
- •Scientific measurements and laboratory work
- •Screen sizes and electronic components
What is an Inch?
An inch (in or ") is a unit of length in the imperial system, equal to 1/12 of a foot or exactly 25.4 millimeters. It's primarily used in the United States, United Kingdom, and Canada for everyday measurements.
Common Uses of Inches
- •Construction and carpentry measurements
- •Screen sizes for TVs, monitors, and phones
- •Plumbing pipe sizes and hardware
- •Height measurements and clothing sizes
Conversion Formula
Inches = Millimeters ÷ 25.4
To convert mm to inches, divide by 25.4
Millimeters = Inches × 25.4
To convert inches to mm, multiply by 25.4
Practical Applications
🔧 Engineering & Manufacturing
Convert between metric and imperial units for accurate machining, 3D printing, and product design.
- CNC machining specifications
- 3D printing dimensions
- Product design tolerances
- Quality control measurements
🏗️ Construction & Woodworking
Convert measurements for building materials, lumber, and construction plans across different systems.
- Lumber dimensions
- Hardware and fastener sizes
- Architectural drawings
- Door and window measurements
📱 Technology & Electronics
Convert screen sizes, component dimensions, and electronic specifications between units.
- Screen and display sizes
- PCB component spacing
- Connector dimensions
- Case and enclosure sizing
🎨 Arts & Crafts
Convert measurements for DIY projects, crafting supplies, and artistic creations.
- Paper and canvas sizes
- Frame dimensions
- Jewelry making
- Model building scales
🚗 Automotive & Mechanical
Convert bolt sizes, part dimensions, and mechanical specifications for vehicle maintenance.
- Bolt and nut sizes
- Tire specifications
- Engine component dimensions
- Tool sizes (wrenches, sockets)
🔬 Science & Medical
Convert precise measurements for laboratory equipment, medical devices, and scientific research.
- Laboratory glassware
- Medical device specifications
- Sample dimensions
- Scientific instrument calibration
Understanding Fractional Inches
Common Fractions Reference
| Fraction | Decimal | MM |
|---|---|---|
| 1/16" | 0.0625" | 1.59 mm |
| 1/8" | 0.1250" | 3.18 mm |
| 3/16" | 0.1875" | 4.76 mm |
| 1/4" | 0.2500" | 6.35 mm |
| 5/16" | 0.3125" | 7.94 mm |
| 3/8" | 0.3750" | 9.53 mm |
| 7/16" | 0.4375" | 11.11 mm |
| 1/2" | 0.5000" | 12.70 mm |
| 5/8" | 0.6250" | 15.88 mm |
| 3/4" | 0.7500" | 19.05 mm |
| 7/8" | 0.8750" | 22.23 mm |
| 1" | 1.0000" | 25.40 mm |
Reading a Ruler
Imperial Ruler (Inches)
- Longest marks: Whole inches (1", 2", 3")
- Second longest: Half inches (1/2")
- Medium marks: Quarter inches (1/4")
- Shorter marks: Eighth inches (1/8")
- Shortest marks: Sixteenth inches (1/16")
Metric Ruler (Millimeters)
- Longest marks: Centimeters (10 mm)
- Medium marks: 5 millimeters
- Short marks: Individual millimeters
- Benefit: Easier to read decimal values
- Precision: More accurate for small measurements
Pro Tips
- Use millimeters for greater precision
- Fractional inches are easier for quick estimates
- Always start measuring from the 1" mark, not the end
- Double-check critical measurements
Frequently Asked Questions
How do I convert mm to inches?
To convert millimeters to inches, divide the millimeter value by 25.4. For example, 100 mm ÷ 25.4 = 3.937 inches. This conversion factor (25.4) is exact and defined by international standards.
How many mm in an inch?
There are exactly 25.4 millimeters in one inch. This is the official definition used worldwide and provides a precise conversion between the metric and imperial systems.
Should I use mm or inches?
It depends on your location, industry, and application. Use millimeters for: engineering specifications, international projects, and scientific work. Use inches for: construction in the US/UK, woodworking, and consumer products in imperial countries. When in doubt, check industry standards or project requirements.
How accurate is the mm to inches conversion?
The conversion factor (25.4 mm = 1 inch) is exact by definition, so conversions are mathematically precise. However, practical accuracy depends on your measuring tools. Digital calipers can measure to 0.01 mm, while standard rulers typically show 1 mm or 1/16 inch increments.
What's the easiest way to estimate mm to inches?
For quick mental estimates, remember these approximations:
- 25 mm ≈ 1 inch (actual: 25.4 mm)
- 10 mm ≈ 3/8 inch (actual: 0.394 inches)
- 5 mm ≈ 3/16 inch (actual: 0.197 inches)
- 1 mm ≈ 1/25 inch (actual: 0.039 inches)