Choose the right length unit
Use this tool for a single length such as a shelf width, a person's height, or a route distance. Millimeters are useful for small tolerances; centimeters and inches suit product dimensions; kilometers and miles suit travel. A nautical mile is a separate unit used at sea and in aviation.
Worked examples
Formula / Calculation Method
1 inch = 2.54 cm; 1 foot = 30.48 cm; 1 mile = 1.609344 km.
How to Use This Tool
- Enter a number using a period for decimals, for example 2.5.
- Choose the From and To units. The result and reference table update as you type.
- Use Swap to reverse the units while keeping your entered value, or Copy Result to save the conversion.
Common Use Cases
Reading a length result
The main feet result is decimal feet. When Feet is selected as the output, a second line gives feet and inches, rounded to two decimal places. To enter 5 ft 8 in, use 5.6666666667 ft or 68 in; entering 5.8 means 5 ft 9.6 in.
Factors use the international foot and mile, not historical US survey units. Displayed results have up to 12 significant digits; that does not increase the precision of your original measurement. For a rectangular area, convert both dimensions and multiply them, or use the area converter if you already know the area.
Common conversions and worked examples
Choose a starting pair, then change the units as needed. The examples below explain how to interpret the result for a specific task.
CM to Feet
A result such as 5.58 ft is a decimal number of feet, not 5 feet 58 inches. This shortcut shows the decimal result and a second, more familiar feet-and-inches line for nonnegative lengths. It is useful for heights, furniture, and room dimensions.
Whole feet = integer part; remaining inches = fractional feet × 12.
Decimal feet versus feet and inches
Read the label of the receiving form. A field requesting decimal feet should receive 5.5774 for 170 cm, while separate feet and inches fields should receive 5 and approximately 6.93. For a whole-inch height, 170 cm rounds to 5 ft 7 in. The companion line rounds inches to two decimals and carries a rounded 12 inches into the next foot.
Feet to CM
The input field expects a single number of feet. Before converting a height written as feet and inches, divide the inches by 12 and add the whole feet. This prevents a common mistake in which 5 ft 8 in is entered as 5.8 ft.
For feet and inches: centimeters = feet × 30.48 + inches × 2.54.
Entering a measurement correctly
5.8 ft converts to 176.784 cm because .8 ft is 9.6 inches. For a mixed measurement, selecting Inches and entering the total inches is often easiest. Keep a measured value's realistic precision; converting a height measured to the nearest inch does not make it accurate to hundredths of a centimeter.
CM to Inches
Use centimeters to inches when comparing a metric dimension with an inch-based product listing. Each dimension must be compared separately. A screen's advertised size is usually its diagonal, so a converted diagonal is not the same as the device width or height.
Using a ruler marked in fractions
The result is decimal inches. To choose a nearby eighth-inch mark, multiply the result by 8, round to a whole number, then divide by 8. For example, 11.811 inches rounds to 11.75 inches at eighth-inch precision. A rounded mark is only an approximation and should not replace a specified engineering tolerance.
Inches to CM
This direction is a multiplication, so many common inch dimensions have a short centimeter result. Enter a fraction as a decimal first: ½ inch is 0.5 and ⅜ inch is 0.375. The unit definition is exact, although real rulers and product dimensions still have tolerances.
Convert all dimensions, not just one
For a box listed as 12 × 8 × 4 inches, the dimensions are 30.48 × 20.32 × 10.16 cm. If the task is about surface area or volume, use square or cubic factors instead of applying 2.54 once to the final area or volume number.
Meters to Feet
Meters and feet describe the same length on different scales. Use this shortcut for one dimension at a time. The result is in international feet, and a companion line expresses a nonnegative result in feet and inches for easier reading.
Length is different from floor area
A room that is 4 m by 3 m has 12 m² of area. Do not enter 12 in this length converter to get square feet. Use the area converter, or convert both room dimensions and multiply the feet results.
Surveying documents may specify a historical survey foot rather than the international foot used here. Use the definition in the document for precise record comparisons.
KM to Miles
The mile used here is the international statute mile, the unit commonly used for road distances. It differs from a nautical mile used at sea and in aviation. A converted distance is the same length; it does not indicate how long a trip will take.
Distance, speed, and nautical miles
If the source says km/h, the value is a speed. Use the speed converter to preserve the time unit. To convert kilometers to nautical miles instead, select Nautical Mile in the To menu. Do not use the road-mile factor for a marine chart.
Miles to KM
Multiply a road-mile distance by 1.609344 to express it in kilometers. This changes the unit without changing the measured route. If an event lists a rounded distance such as 26.2 miles, converting that number cannot recover a more precise official course length.
Keep the original reading's precision
An odometer reading displayed to a tenth of a mile does not gain finer measurement accuracy when the converter shows more decimals. Keep extra digits while calculating totals, then round the final value to a precision appropriate to the source. For miles per hour, use the speed converter; for nautical miles, change the From selector.