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Length Unit Conversion — Formulas & Quick Reference
All length conversions trace back to one exact relationship: 1 inch = 25.4 mm exactly (defined internationally in 1959). Everything else follows from there.
Core Conversion Relationships
Worked Example: Convert 5 ft 7 in to cm
Converting Fractions of an Inch
Fractional inches are common in woodworking, construction, and machining. To convert to decimal, divide numerator ÷ denominator. Then multiply by 25.4 for mm.
Height in Feet & Inches ↔ CM
- cm → ft: divide cm by 30.48, floor = feet, remainder × 12 = inches
- ft in → cm: (feet × 12 + inches) × 2.54
- Example: 175 cm = 5 ft 8.9 in ≈ 5′9″
- Example: 6 ft 0 in = 182.88 cm
Length Conversion Reference Tables (2026)
Quick lookup for the most common conversions. Use the calculator above for any value.
Inches to CM — Common Values
| Inches | CM | MM | Feet | Meters |
|---|---|---|---|---|
| 1 in | 2.54 cm | 25.4 mm | 0.0833 ft | 0.0254 m |
| 2 in | 5.08 cm | 50.8 mm | 0.167 ft | 0.0508 m |
| 3 in | 7.62 cm | 76.2 mm | 0.25 ft | 0.0762 m |
| 4 in | 10.16 cm | 101.6 mm | 0.333 ft | 0.1016 m |
| 6 in | 15.24 cm | 152.4 mm | 0.5 ft | 0.1524 m |
| 12 in | 30.48 cm | 304.8 mm | 1 ft | 0.3048 m |
| 18 in | 45.72 cm | 457.2 mm | 1.5 ft | 0.4572 m |
| 24 in | 60.96 cm | 609.6 mm | 2 ft | 0.6096 m |
| 36 in | 91.44 cm | 914.4 mm | 3 ft | 0.9144 m |
| 48 in | 121.92 cm | 1219.2 mm | 4 ft | 1.2192 m |
CM to Feet & Inches — Height Reference
| CM | Feet & Inches | Decimal Feet | Meters |
|---|---|---|---|
| 150 cm | 4′ 11.1″ | 4.921 ft | 1.50 m |
| 155 cm | 5′ 1.0″ | 5.085 ft | 1.55 m |
| 160 cm | 5′ 3.0″ | 5.249 ft | 1.60 m |
| 163 cm | 5′ 4.2″ | 5.348 ft | 1.63 m |
| 165 cm | 5′ 5.0″ | 5.413 ft | 1.65 m |
| 170 cm | 5′ 6.9″ | 5.577 ft | 1.70 m |
| 175 cm | 5′ 8.9″ | 5.741 ft | 1.75 m |
| 180 cm | 5′ 10.9″ | 5.906 ft | 1.80 m |
| 183 cm | 6′ 0.0″ | 6.004 ft | 1.83 m |
| 185 cm | 6′ 0.9″ | 6.070 ft | 1.85 m |
| 190 cm | 6′ 2.8″ | 6.234 ft | 1.90 m |
| 200 cm | 6′ 6.7″ | 6.562 ft | 2.00 m |
Fractional Inches to MM & Decimal
| Fraction | Decimal (in) | MM | CM |
|---|---|---|---|
| 1/32 | 0.03125 | 0.794 mm | 0.0794 cm |
| 1/16 | 0.0625 | 1.588 mm | 0.159 cm |
| 1/8 | 0.125 | 3.175 mm | 0.318 cm |
| 3/16 | 0.1875 | 4.763 mm | 0.476 cm |
| 1/4 | 0.25 | 6.35 mm | 0.635 cm |
| 5/16 | 0.3125 | 7.938 mm | 0.794 cm |
| 3/8 | 0.375 | 9.525 mm | 0.953 cm |
| 7/16 | 0.4375 | 11.113 mm | 1.111 cm |
| 1/2 | 0.5 | 12.7 mm | 1.27 cm |
| 5/8 | 0.625 | 15.875 mm | 1.588 cm |
| 3/4 | 0.75 | 19.05 mm | 1.905 cm |
| 7/8 | 0.875 | 22.225 mm | 2.223 cm |
Meters to Feet — Distance Reference
| Meters | Feet | Ft & In | Yards | Inches |
|---|---|---|---|---|
| 0.5 m | 1.640 ft | 1′ 7.7″ | 0.547 yd | 19.685 in |
| 1 m | 3.281 ft | 3′ 3.4″ | 1.094 yd | 39.370 in |
| 1.5 m | 4.921 ft | 4′ 11.1″ | 1.640 yd | 59.055 in |
| 2 m | 6.562 ft | 6′ 6.7″ | 2.187 yd | 78.740 in |
| 3 m | 9.843 ft | 9′ 10.1″ | 3.281 yd | 118.11 in |
| 5 m | 16.404 ft | 16′ 4.8″ | 5.468 yd | 196.85 in |
| 10 m | 32.808 ft | 32′ 9.7″ | 10.936 yd | 393.70 in |
| 100 m | 328.08 ft | 328′ 1″ | 109.36 yd | 3,937 in |
When to Use Each Unit — Metric vs Imperial
The world uses two main systems. The US uses imperial (inches, feet, miles). Almost everywhere else uses metric (mm, cm, m, km). Understanding both prevents costly errors in construction, manufacturing, and science.
Metric Units
- Millimeters (mm): Woodworking, machining, bolt sizes, blueprints, 3D printing
- Centimeters (cm): Clothing sizes, human body measurements, furniture, school
- Meters (m): Room dimensions, fabric, swimming pool lengths, sports fields
- Kilometers (km): Road distances, running/cycling routes, maps
Imperial / US Customary
- Inches (in): Screen sizes (TVs, phones), pipe diameters, tire widths, US manufacturing
- Feet (ft): Room height, ceiling height, real estate, US construction
- Yards (yd): American football, fabric in the US, some landscaping
- Miles (mi): Road distances in US/UK, running races
Why Conversions Matter
Mixing metric and imperial without converting caused the famous Mars Climate Orbiter crash in 1999 — a $327M spacecraft lost because one team used pound-seconds and another used newton-seconds.
Common Real-World Needs
- Buying IKEA furniture: Dimensions are in cm — need feet/inches for US rooms
- Ordering bolts online: US specs in inches; European in mm
- Medical records: Height may be in cm in some countries, ft/in in others
- Screen size shopping: TV diagonals in inches; some specs in cm
- Sewing & knitting patterns: US patterns in inches; European in cm
- 3D printing files: STL units may be mm or inches depending on origin
Length Converter — Frequently Asked Questions
Answers to the most common questions about converting inches, cm, feet, mm, and meters.