Imperial to Metric Converter

Which units does the converter handle?

The upper row accepts six imperial and nautical length units, and the lower row can display the result in any of seven metric units. Every pairing is available, so you can go from inches to nanometers just as easily as from leagues to kilometers.

The metric side runs from the very small to the large: nanometers (nm), micrometers (μm), millimeters (mm), centimeters (cm), decimeters (dm), meters (m) and kilometers (km). Neighbouring metric units differ by a factor of 10 or 1,000, which is what makes mental conversion easy.

Imperial and metric length units compared

The metric system was designed in France in the 1790s around a single base unit, the meter, and prefixes that scale it by powers of ten. Today the meter is fixed by the speed of light: the distance light travels in a vacuum in 1/299,792,458 of a second. Because everything else is a decimal multiple, converting within the system only means moving a decimal point.

Imperial units grew out of older English measures such as the barleycorn, the foot and the pace, and were tidied up by a series of British statutes. The United States kept a closely related set called US customary units. Nothing in the imperial scale is decimal: 12 inches make a foot, 3 feet a yard and 1,760 yards a mile.

Since 1959 the two worlds have been tied together by agreement. The international yard is exactly 0.9144 m, which makes the inch exactly 25.4 mm. Every conversion on this page therefore multiplies by a precise constant, and the only inexactness is how many digits are displayed.

How to convert imperial to metric

1. Type your length in the top box and pick its unit from the list beside it.
2. Choose the metric unit you want in the second row.
3. The converted value appears at once. Change either unit and it updates again.

metric length = imperial length × (meters per imperial unit) ÷ (meters per metric unit)Example: inches to centimeters is × 0.0254 ÷ 0.01, which is × 2.54.

Large results get thousands separators and long results are rounded to nine decimals, with trailing zeros removed. A very small answer may be written in exponent form, for example 2.5e-8.

Quick reference tables

Mental shortcuts for everyday lengths

You do not always need nine decimals. These round-number versions are close enough to size up a room, a trip or a screen:

• 1 inch is about 2.5 cm (exactly 2.54).
• 1 foot is about 30 cm (exactly 30.48), so a 6-foot person is roughly 1.8 m tall.
• 1 yard is a little under a meter (0.9144 m).
• 1 mile is about 1.6 km. Multiply the miles by 8 and divide by 5 for a good estimate: 50 miles is about 80 km (exactly 80.4672).

Estimates drift as the numbers grow, so switch to the converter when the answer matters, for instance in a material order or a navigation plan.

Common mistakes

• Mixing statute and nautical miles. A nautical mile is 1.852 km, about 15% longer than the 1.609 km statute mile.
• Applying a length factor to an area or volume. Squares and cubes need the factor squared or cubed: 1 square inch is 6.4516 cm² (2.54 × 2.54), and 1 cubic inch is 16.387064 cm³ (2.54 × 2.54 × 2.54).
• Treating 5 ft 6 in as 5.6 ft. Six inches is half a foot, so 5 ft 6 in is 5.5 ft, or 1.6764 m.
• Rounding too early. Keep all digits until the final step, then round once.

Accuracy and special cases

The nautical mile is routed through statute miles using the constant 1.150779448, so a result such as 2.5 nautical miles in millimeters can differ from the exact 4,630,000 mm by a fraction of a micrometer. The league follows the common definition of three statute miles; older and regional leagues varied from country to country.

Results are mathematical conversions. For engineering drawings, legal land descriptions or trade, follow the rounding rules of your own standard. If you work with very large or tiny numbers, the scientific notation calculator helps with the exponent form.

For single pairs, dedicated pages such as miles to kilometers, feet to meters and inches to centimeters give a focused guide and table.