Essential for 3D printing, international manufacturing, and metric system projects. Convert fractional inches (1/2", 1/4", 1/8") to precise millimeter values.
3D Printing • 0-6"
Range: 0-6" • Step: 0.125" • Precision: 1 decimal
| Inches (Fraction) | Inches (Decimal) | Millimeters (mm) |
|---|---|---|
| 0" | 0.0000" | 0 mm |
| 1/8" | 0.1250" | 3.2 mm |
| 1/4" | 0.2500" | 6.3 mm |
| 3/8" | 0.3750" | 9.5 mm |
| 1/2" | 0.5000" | 12.7 mm |
| 5/8" | 0.6250" | 15.9 mm |
| 3/4" | 0.7500" | 19 mm |
| 7/8" | 0.8750" | 22.2 mm |
| 1" | 1.0000" | 25.4 mm |
| 1 1/8" | 1.1250" | 28.6 mm |
| 1 1/4" | 1.2500" | 31.8 mm |
| 1 3/8" | 1.3750" | 34.9 mm |
| 1 1/2" | 1.5000" | 38.1 mm |
| 1 5/8" | 1.6250" | 41.3 mm |
| 1 3/4" | 1.7500" | 44.4 mm |
| 1 7/8" | 1.8750" | 47.6 mm |
| 2" | 2.0000" | 50.8 mm |
| 2 1/8" | 2.1250" | 54 mm |
| 2 1/4" | 2.2500" | 57.1 mm |
| 2 3/8" | 2.3750" | 60.3 mm |
| 2 1/2" | 2.5000" | 63.5 mm |
| 2 5/8" | 2.6250" | 66.7 mm |
| 2 3/4" | 2.7500" | 69.8 mm |
| 2 7/8" | 2.8750" | 73 mm |
| 3" | 3.0000" | 76.2 mm |
| 3 1/8" | 3.1250" | 79.4 mm |
| 3 1/4" | 3.2500" | 82.5 mm |
| 3 3/8" | 3.3750" | 85.7 mm |
| 3 1/2" | 3.5000" | 88.9 mm |
| 3 5/8" | 3.6250" | 92.1 mm |
| 3 3/4" | 3.7500" | 95.3 mm |
| 3 7/8" | 3.8750" | 98.4 mm |
| 4" | 4.0000" | 101.6 mm |
| 4 1/8" | 4.1250" | 104.8 mm |
| 4 1/4" | 4.2500" | 107.9 mm |
| 4 3/8" | 4.3750" | 111.1 mm |
| 4 1/2" | 4.5000" | 114.3 mm |
| 4 5/8" | 4.6250" | 117.5 mm |
| 4 3/4" | 4.7500" | 120.6 mm |
| 4 7/8" | 4.8750" | 123.8 mm |
| 5" | 5.0000" | 127 mm |
| 5 1/8" | 5.1250" | 130.2 mm |
| 5 1/4" | 5.2500" | 133.3 mm |
| 5 3/8" | 5.3750" | 136.5 mm |
| 5 1/2" | 5.5000" | 139.7 mm |
| 5 5/8" | 5.6250" | 142.9 mm |
| 5 3/4" | 5.7500" | 146 mm |
| 5 7/8" | 5.8750" | 149.2 mm |
| 6" | 6.0000" | 152.4 mm |
Formula: mm = inches × 25.4
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Essential tips for converting inches to millimeters accurately
Our chart displays common fractions (1/2", 1/4", 1/8", 1/16") alongside their decimal equivalents and exact mm values.
Example:
1/2" = 0.500" = 12.7 mm
3/8" = 0.375" = 9.5 mm
Tip: Most tape measures use 1/16" as the smallest division. For finer work, use digital calipers.
Select step size based on your application:
⚠️ Note: Finer steps create longer charts. Balance detail vs. length.
⚠️ Important: Verify accuracy by measuring a known distance on the printed chart before use.
Real-world scenarios where inches to mm conversion is essential
Most 3D modeling software (Fusion 360, Blender, Tinkercad) uses millimeters as the default unit. Convert American measurements to create accurate models and ensure proper fit.
💡 Recommended: 0-12" range with 1/8" or 0.1" steps
PCB layouts typically use metric units (mm), but many electronic components are sized in inches. Ensure proper fit when mixing American and international parts.
💡 Recommended: 0-6" range with 0.1" decimal steps
When sourcing parts globally or collaborating with international teams, convert American specifications to metric standards for accurate communication and production.
💡 Recommended: 1-12" range with 1/16" fraction steps
The Formula
Example Calculation:
Problem: Convert 2.5 inches to mm
Step 1: 2.5 × 25.4
Step 2: = 63.5
Answer: 2.5 inches = 63.5 mm
The magic number 25.4 comes from the 1959 international agreement that standardized the inch across all countries.
1 inch = exactly 25.4 millimeters
This definition is exact (not an approximation), which means:
💡 Memory Trick: "Twenty-five point four" - say it out loud 3 times and you'll never forget!
For quick estimates, multiply by 25 instead of 25.4
Memorize common conversions and scale from there
Common fractions have easy-to-remember mm values
Why calculate when you can look it up instantly?
Understand the difference and choose the right chart for your needs
| Aspect | 📏 Inches to MMThis Page | 📐 MM to Inches |
|---|---|---|
| Primary Users | 🇺🇸 US, Canada (imperial countries) | 🌍 Europe, Asia, South America (metric countries) |
| Common Scenarios |
|
|
| Input Format | Fractions (1/2", 1/4") or decimals (0.5", 0.25") | Whole numbers (1mm, 10mm, 50mm) |
| Output Precision | 1-2 decimal places (6.4mm, 12.70mm) | Fractions (25/64") or decimals (0.394") |
| Typical Range | 1" - 12" (small to medium objects) | 1mm - 100mm (small parts) |
| Formula | mm = inches × 25.4 | inches = mm ÷ 25.4 |
Need the reverse conversion?
Go to MM to Inches ChartExplore more free printable charts to complete your toolkit
Reverse conversion from millimeters to inches
Convert inch fractions to decimal values
Centimeter to inch conversion for height & length
AWG to mm² wire size conversion
1 inch equals exactly 25.4 millimeters. This is the internationally standardized definition established in 1959. The conversion is exact (not an approximation), meaning there's no rounding error when you multiply or divide by 25.4. For example: 1 inch = 25.4 mm (exact), 2 inches = 50.8 mm, and 10 inches = 254 mm.
First convert the fraction to a decimal, then multiply by 25.4. For example, to convert 3/8 inch to mm: Step 1: 3 ÷ 8 = 0.375 inches. Step 2: 0.375 × 25.4 = 9.525 mm. Answer: 3/8" = 9.525 mm (or rounded to 9.5 mm). Our chart shows both fractions and their mm equivalents - no math needed!
For most 3D printing projects, a 0-12 inch range with 1/8" or 0.1" steps works perfectly. This covers small prints (0-3 inches / 0-76mm), medium prints (3-6 inches / 76-152mm), and large prints (6-12 inches / 152-305mm). If your printer bed is larger (e.g., 16" × 16"), consider extending the range to 0-16 inches.
Use decimals for technical work (3D printing, CNC programming, digital calipers, CAD software) where precision is key. Use fractions for traditional measuring (reading tape measures, woodworking with traditional tools, following American blueprints, communicating with non-technical users). Our chart shows both formats - choose what you need!
Our conversion is mathematically exact. We use the official conversion factor (25.4) without any rounding until the final display. 1 decimal place (6.4mm) gives ±0.05mm accuracy - perfect for general use. 2 decimal places (6.35mm) gives ±0.005mm accuracy - suitable for precision work. For 99% of applications (including professional machining), 1-2 decimal places is more than sufficient.
Yes! PCB design frequently requires mixing imperial and metric units. Common conversions include: Standard pin spacing (0.1" = 2.54mm), SMD component sizes (0603 in inches vs 1608 in mm), mounting holes (1/8" = 3.175mm), and board thickness (1/16" = 1.6mm). Recommended settings for PCB work: Range 0-2 inches, Steps 0.01" or 0.1" decimals, Precision 2 decimal places for mm.
We're here to help with your conversion needs.
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