Units & Numbers Converters

Convert length, area, volume, speed and data units, shoe sizes and Roman numerals.

Unit conversion fails in two ways: using the wrong factor, or rounding too early. Each converter here shows the factor it used. The length converter covers metric and imperial lengths, the area unit converter covers square units, acres and hectares, and the volume converter covers liters, gallons and cups.

The speed converter switches between mph, km/h, knots and meters per second. The data storage and bandwidth converter separates decimal units (GB) from binary units (GiB) and bits from bytes, which explains why a drive looks smaller than advertised. The shoe size converter and the Roman numerals converter handle two conversions with no single formula. Sizes vary by brand, so use shoe sizes as a guide. When a result is going into a purchase order or a specification, convert once from the original value rather than chaining conversions.

Popular units & numbers converters

• Length ConverterMeters, feet, inches, miles and more, with the factor shown.
• Volume ConverterLiters, gallons, cups and other volumes, US and imperial.
• Data Units ConverterBytes, bits, KB, KiB, GB and GiB, plus transfer speeds.
• Speed Convertermph, km/h, knots and meters per second.

All units & numbers converters

• Roman Numerals ConverterType a whole number to see its Roman numeral, or type a Roman numeral such as MCMXCIV to see the number. The answer updates as you type.
• Data Units ConverterPick a number, a unit to convert from and a unit to convert to. Storage sizes convert to storage sizes and transfer speeds to transfer speeds; tick the SI box to count in thousands instead of 1,024s. The binary names, KiB to EiB, always count in 1,024s.
• Length ConverterPick a unit, type a length, choose the unit you want and read the answer. The converter covers metric, imperial and nautical units in one place.
• Area ConverterPick a unit on each side, type an area and the converted value appears straight away. Every conversion passes through square meters, using exact factors such as 1 acre = 4,046.8564224 m².
• Volume ConverterPick a number and two units to convert between 25 metric, US and imperial volume units, from cubic kilometers down to teaspoons. The answer updates as you type.
• Speed ConverterEnter a speed, choose the unit you have and the unit you want, and the answer appears at once with up to ten decimals. Six units are covered, from road speeds to marine knots.
• Shoe Size ConverterChoose women's, men's or children's, pick the size system you know and the size you have, then choose the system you want to see. Sizes without an equivalent show N/A.