Length Converter

Choose the measured dimension

Identify which length is stated: width, height, depth or distance. Keep that dimension’s description with its number. A width conversion does not supply an object’s depth or the clearance around it.

For a hypothetical product width of 120 cm, divide by 2.54 cm/in: 120 / 2.54 ≈ 47.24409449 in, displayed to ten significant digits. The calculator’s default four-decimal display is 47.2441 in.

• Centimeters to inches
• Inches to centimeters

Identify linear units and definitions

BIPM identifies the meter (m) as the SI base unit for length; modern SI definitions fix defining constants. Decimal prefixes give 1 km = 1000 m, 1 cm = 0.01 m and 1 mm = 0.001 m.

The international foot is exactly 0.3048 m. With 12 inches per foot and 3 feet per yard, the international inch is 0.0254 m and the yard is 0.9144 m. NIST’s revised table distinguishes these from historic U.S. survey-foot units. Check the source definition rather than inferring it from the country name.

• Compare unit systems and conventions
• Feet to inches
• Yards to feet

Convert before comparing specifications

Compare the same dimension in a common unit. A hypothetical 3 m length is 3 / 0.3048 ≈ 9.842519685 ft at ten significant digits, or 9.8425 ft at four decimal places. Convert each required dimension separately before making a fit comparison.

NIST distinguishes nominal lumber names from actual finished dimensions. A nominal 2×4 label is not an instruction to assume measured sides of 2 inches and 4 inches. Use the actual dimensions and applicable clearance or tolerance rather than relying on a unit conversion to guarantee fit.

• Meters to feet
• Feet to meters
• Construction measurement examples
• Package measurement examples

Distinguish miles and nautical miles

The international mile is exactly 1609.344 m = 1.609344 km. NIST SP 811 footnote 20 records the international nautical mile as exactly 1852 m. These are different length units. Use the unit named by a distance reference, including a navigation document; do not substitute one for the other.

A fixed nautical-mile definition does not establish the distance of an actual latitude arc at every location. This converter re-expresses a supplied distance and does not provide route, range or operational navigation guidance.

• International miles to kilometers
• Kilometers to international miles
• Nautical miles to international miles
• Named aviation quantities
• Separate trip distance and speed

Preserve measurement precision

An exact unit definition does not make a supplied measurement exact. Use the source’s stated convention and justified precision, calculate from definitions, and round the final display. Published conversion tables may round their factors; the calculator also uses floating-point arithmetic. More display digits do not establish more measurement accuracy.

The retained light-year converters use a Julian-year derivation: 365.25 days × 86400 seconds/day × 299792458 m/s = 9460730472580800 m. IAU’s recommendations and NASA/JPL parameters document those inputs. That is a distance convention, not a measured star distance; the specialist pages identify their own source scope.

• Sources, arithmetic and rounding
• Light-year derivation in centimeters

Use area tools for squared dimensions

A length converter handles m, cm, ft and other linear units. An area in m² or ft² has two length dimensions, so its factor is squared. For a rectangle, first express both side lengths in the same length unit and multiply them; then convert the resulting area. A linear conversion does not calculate an irregular shape’s area.

• Area definitions and worked rectangles

Sources and review

• NIST: exact international foot and mile, with survey-foot distinction
• NIST Handbook 44 Appendix C: inch, foot and yard relationships
• NIST SP 811 footnote 20: international nautical mile
• BIPM: SI length base unit and modern defining constants
• BIPM: decimal prefix multipliers
• NIST: nominal and actual lumber dimensions
• IAU: Julian-year and day conventions
• NASA/JPL: Julian year, day and speed of light inputs

Reviewed 2026-10-06. Calculated values are displayed to at most ten significant digits; extra digits do not establish measurement accuracy.