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Length Conversion Reference: Centimeters, Inches, Feet, Miles and More
A practical reference for converting between centimeters, millimeters, inches, feet, meters, kilometers and miles, with real-world examples for paper sizes, screen dimensions and everyday objects.
This reference covers the length units people convert most often: centimeters, millimeters, inches, feet, meters, kilometers and miles. The relationships below are exact where they are defined by agreement, and the examples use real objects you can measure yourself.
How the units relate
The inch is defined as exactly 2.54 centimeters under the international agreement of 1959, so conversions involving inches are exact rather than estimated. Everything else follows from that.
| Unit | Equals |
|---|---|
| 1 inch | 2.54 centimeters (exact) |
| 1 foot | 12 inches = 30.48 centimeters |
| 1 yard | 3 feet = 0.9144 meters |
| 1 mile | 1,609.344 meters = 1.609344 kilometers (exact) |
| 1 meter | 100 centimeters = 1,000 millimeters |
| 1 kilometer | 1,000 meters ≈ 0.621371 miles |
| 1 centimeter | 10 millimeters ≈ 0.393701 inches |
Real-world reference sizes
These are common, standardized sizes — useful when you need to picture what a measurement actually means.
| Object | Typical size |
|---|---|
| A4 paper | 210 × 297 mm (8.27 × 11.69 in) |
| US Letter paper | 8.5 × 11 in (215.9 × 279.4 mm) |
| Credit card (ID-1) | 85.60 × 53.98 mm (3.37 × 2.13 in) |
| Screen / TV size | Measured diagonally in inches; a 24 in screen is about 61 cm diagonally |
| Interior door height | About 203 cm (80 in); varies by region |
Feet and inches
Feet and inches are read together: 5 feet 10 inches is 70 inches total, which is 177.8 centimeters. A foot is always 12 inches, so convert feet to inches first (multiply by 12), then add the extra inches, then multiply by 2.54 to get centimeters.
Which tool to use
Pick the tool that matches the units you are converting between:
- Converting between centimeters and inches (for example, a product size listed in cm you think about in inches): CM to Inches Converter
- Converting between millimeters and inches (for example, a small part measured in mm): MM to Inches Converter
- Converting between kilometers and miles (for example, a road distance or race): KM to Miles Converter
How precise do you need to be?
The right level of precision depends on what you are measuring and why. Use this as a rough guide:
- Everyday estimates: rounding to the nearest inch or centimeter is usually enough for household items, furniture fit and general shopping.
- Printing and paper: use exact standard sizes such as A4 (210 × 297 mm) or US Letter (8.5 × 11 in). Small rounding errors can shift margins and cut off content.
- Technical or engineering: carry more decimal places and do not round until the final result, especially when units are chained together.
- Cooking and household: whole centimeters or inches are typically fine; exact millimeters rarely matter.
Everyday conversion examples
These are common sizes you can use as reference points:
| Object | Metric | Imperial |
|---|---|---|
| Standard ruler | 30 cm | 11.81 in |
| Foot | 30.48 cm | 12 in (exact) |
| 4 x 6 in photo print | 10.16 x 15.24 cm | 4 x 6 in |
| US passport photo | 51 x 51 mm | 2 x 2 in |