Metric Converter

Which units are supported?

Both selectors list the same thirteen units, so you can convert within the metric system, within the imperial system, or across the two. Internally every length passes through meters, which keeps the factors simple and the results consistent.

Metric, imperial and nautical units

The metric system is decimal. Each prefix stands for a power of ten, so moving between millimeters, centimeters, meters and kilometers is a matter of shifting the decimal point by 1, 2 or 3 places. That simplicity is the main reason it became the worldwide standard for science, engineering and trade.

The imperial system, still in daily use in the United States and partly in the United Kingdom, mixes bases: 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile. Since the 1959 yard and pound agreement each imperial length has an exact metric definition, so conversions between the systems are precise, only less tidy.

The nautical mile belongs to ships and aircraft. It is tied to the Earth's geometry, close to one minute of latitude, and was fixed at 1,852 meters by international agreement in 1929.

How the conversion works

1. Type the length in the upper box and select its unit.
2. Select the unit you want in the lower row.
3. The converted value appears immediately and refreshes whenever you edit a number or a unit.

result = length × (meters per source unit) ÷ (meters per target unit)Using the table above, 1 mile in feet is 1,609.344 ÷ 0.3048 = 5,280.

Results are rounded to nine decimals with trailing zeros dropped, and numbers above 999 get thousands separators. Answers below one millionth are written in exponent form, such as 2.5e-8.

Quick reference tables

A feel for the scales

Thirteen units spanning twelve orders of magnitude are easier to use when you can picture them. The table pairs familiar objects with a typical size.

Common mistakes

• Mixing up m and mm, or μm and mm. A factor of 1,000 is easy to lose when you are reading a spec sheet quickly.
• Using the same factor for area and volume. Squares and cubes need the length factor squared or cubed.
• Assuming every mile is the same. The statute mile is 1,609.344 m and the nautical mile is 1,852 m.
• Copying rounded intermediate values. Convert once from the original number rather than chaining several rounded conversions.

Tips for reliable results

Keep units in view when you copy a number: a plain "10" can be meters or miles, and the difference is a factor of more than 1,600. If the answer looks implausible, check that both selectors say what you expect.

For common pairs, the dedicated pages metric to imperial and imperial to metric give a focused guide. Numbers with long strings of zeros can be rewritten with the scientific notation calculator.

The converter treats a league as three statute miles (4.828032 km). Historical leagues varied, so check the source if you are converting a figure from an old text.