How to convert units of length
- 1.
Enter a value
Type a number in the Value field - both 27.5 and 27,5 work.
- 2.
Pick units
Choose the source unit (e.g. inch) and the target unit (e.g. cm).
- 3.
Read the result
The result updates live. Below it you get the value in every length unit and a table of common conversions.
- 4.
Reverse the direction
The swap button flips the units, turning "inches to cm" into "cm to inches".
Exact length conversions
Every imperial and US length unit is defined in terms of the metre, so these conversions are exact, not approximations:
| Unit | In metres | Notes |
|---|---|---|
| 1 inch (in, ″) | 0.0254 m = 2.54 cm | exact since 1959 |
| 1 foot (ft, ′) | 0.3048 m = 30.48 cm | = 12 inches |
| 1 yard (yd) | 0.9144 m | = 3 feet = 36 inches |
| 1 mile (mi) | 1609.344 m ≈ 1.609 km | = 1760 yards = 5280 feet |
| 1 nautical mile (nmi) | 1852 m | used at sea and in aviation |
| 1 kilometre (km) | 1000 m ≈ 0.6214 mi |
Rules to remember: cm = inches × 2.54, inches = cm ÷ 2.54 and km = miles × 1.609344.
Inches to centimetres: screens, wheels and paper
Screen diagonals and bicycle wheels are quoted in inches almost everywhere. Example: a 27″ monitor is 27 × 2.54 = 68.58 cm across the diagonal.
| Inches | Centimetres | Typical use |
|---|---|---|
| 1″ | 2.54 cm | base unit |
| 8.5″ × 11″ | 21.59 × 27.94 cm | US Letter paper |
| 24″ | 60.96 cm | office monitor |
| 27″ | 68.58 cm | monitor |
| 55″ | 139.7 cm | TV |
| 65″ | 165.1 cm | large TV |
| 29″ | 73.66 cm | mountain bike wheel |
The diagonal is not the width of a screen - to get the width and height, use the aspect ratio calculator.
Height in feet and inches
Height in cm = (feet × 12 + inches) × 2.54. For example 5′ 9″ = 69 in × 2.54 = 175.26 cm.
| Height | Total inches | Centimetres |
|---|---|---|
| 5′ 0″ | 60″ | 152.4 cm |
| 5′ 6″ | 66″ | 167.64 cm |
| 5′ 9″ | 69″ | 175.26 cm |
| 6′ 0″ | 72″ | 182.88 cm |
| 6′ 2″ | 74″ | 187.96 cm |
A common mistake is reading 5.9 ft as 5′ 9″. In fact 5.9 ft is 5 feet 10.8 inches (179.8 cm) - multiply the decimal part of a foot by 12 to get inches.
Miles, kilometres and nautical miles
A statute mile (1.609 km) and a nautical mile (1.852 km) are different units: the nautical mile is about 15% longer and is used for ship and aircraft distances, while speed at sea is given in knots (nautical miles per hour). A marathon (42.195 km) is about 26.22 miles; a 5K run is 3.11 miles and a 10K is 6.21 miles. The quick estimate "miles × 1.6" is off by 0.93 km per 100 miles, so use the full factor for long routes.
Frequently asked questions
How many cm are in an inch?
+
Exactly 2.54 cm (25.4 mm), fixed by international agreement in 1959.
How do I convert cm to inches?
+
Divide centimetres by 2.54. Example: 30 cm ÷ 2.54 = 11.81 inches.
How many kilometres are in a mile?
+
1 mile = 1.609344 km exactly. For a quick estimate multiply miles by 1.6.
How many feet are in a metre?
+
1 metre = 3.2808 feet; 1 foot = 0.3048 m.
What is the difference between a mile and a nautical mile?
+
A statute mile is 1609.344 m; a nautical mile is 1852 m, about 15% longer.
Is the converter exact?
+
Yes. All units are converted through the metre using their exact definitions; results are shown with up to 7 significant digits.
Updated: