Have you ever encountered foreign product dimensions and wondered: "How many centimeters is a 32-inch monitor?", "What diameter in millimeters is a 1/4-inch screw?", or "How many millimeters will a 100-pixel digital element measure when printed?"
While Japan and most of the world use the metric system (millimeters and centimeters), imports, display screens, jeans waist sizes, tripod mounts, and digital web design frequently rely on inches and pixels.
This comprehensive guide covers exact mathematical conversion formulas between mm, cm, inches, and pixels, fraction-to-millimeter charts, screen DPI/PPI math, and practical tips for switching units instantly on Jougi Online.
1. Fundamental Length Units & Conversion Formulas
By international treaty (the International Yard and Pound Agreement), 1 inch is legally and precisely defined worldwide as:
1 inch = 25.4 millimeters = 2.54 centimeters
Conversion Formulas Summary
- Millimeters to Centimeters:
cm = mm / 10 - Centimeters to Millimeters:
mm = cm × 10 - Inches to Millimeters:
mm = inch × 25.4 - Millimeters to Inches:
inch = mm / 25.4 ≈ mm × 0.03937 - Inches to Centimeters:
cm = inch × 2.54 - Centimeters to Inches:
inch = cm / 2.54 ≈ cm × 0.3937
2. Whole Inches to Millimeters & Centimeters Lookup Table (1" to 30")
| Inches (in) | Millimeters (mm) | Centimeters (cm) | Common Reference Example |
|---|---|---|---|
| 1/4" (0.25 in) | 6.35 mm | 0.635 cm | Camera tripod screw (UNC 1/4"), audio plug |
| 1/2" (0.50 in) | 12.70 mm | 1.27 cm | Plumbing pipe diameter, bolts |
| 1" (1.00 in) | 25.40 mm | 2.54 cm | International standard inch, 1-inch camera sensor |
| 2" | 50.80 mm | 5.08 cm | Badge button size, ribbon width |
| 4" | 101.60 mm | 10.16 cm | Early iPhone screen diagonal |
| 6" | 152.40 mm | 15.24 cm | Standard smartphone display diagonal |
| 10" | 254.00 mm | 25.40 cm | Standard iPad tablet display (10.2" to 10.9") |
| 12" (1 ft) | 304.80 mm | 30.48 cm | Vinyl LP record, 1 foot |
| 13.3" | 337.82 mm | 33.78 cm | Classic MacBook Air display diagonal |
| 24" | 609.60 mm | 60.96 cm | Standard desktop computer monitor |
| 27" | 685.80 mm | 68.58 cm | High-resolution 4K / WQHD workstation display |
| 32" | 812.80 mm | 81.28 cm | Bedroom television display diagonal |
3. Fractional Inch (1/32, 1/16, 1/8) to Millimeter Table
Mechanical fasteners, camera fittings, and American workshop tools use fractional inch denominations:
| Fractional Inch | Decimal Inch | Millimeters (mm) | Applications |
|---|---|---|---|
| 1/16" | 0.0625 in | ~1.59 mm | Miniature pins, shim washers |
| 1/8" | 0.1250 in | ~3.18 mm | 3.5 mm mini audio jack original standard |
| 1/4" | 0.2500 in | 6.35 mm | Camera tripod mount screw (UNC 1/4") |
| 3/8" | 0.3750 in | 9.53 mm | Large tripod head mounting thread (UNC 3/8") |
| 1/2" | 0.5000 in | 12.70 mm | Water pipe plumbing, standard bolt size |
4. Converting Pixels (px) to Millimeters (mm) & PPI/DPI
To convert on-screen pixels to physical millimeters, you must know the target display or print medium's resolution (PPI or DPI):
Length (mm) = (Pixel Count / PPI) × 25.4
Pixel Count (px) = (Length in mm / 25.4) × PPI
5. Instant Unit Switching on Jougi Online
On Jougi Online, clicking the "Unit" toggle (mm / cm / inch / px) updates the ruler scale immediately without losing your caliper pin positions, allowing you to cross-reference millimeter and fractional inch measurements at a glance.