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Unit Converter

Type a value and pick two units to convert between 23 measures, from length and weight to temperature, data and energy, with a table of common amounts.

1 cm = 0.3937008 in

1 cm0.3937008 in
2 cm0.7874016 in
5 cm1.968504 in
10 cm3.937008 in
20 cm7.874016 in
50 cm19.68504 in
100 cm39.37008 in
1,000 cm393.7008 in
The unit converter set to length, showing that 10 kilometers equal 6.213712 miles

Guide

How the unit converter works and where its numbers come from

How to convert a value

  1. Open the Measure list and choose what you are measuring. The list is searchable: type “temp” or “press” to filter it. The page opens on length, converting 1 centimetre to inches.
  2. Choose the From unit and the To unit. Each entry shows the symbol and the name, for example ft-us - US Survey Foot, which helps when two units have similar names.
  3. Type the number in the Origin value field. A comma or a point both work as the decimal separator: 1,5 and 1.5 are read the same way, and 1 234,56 or 1,234.56 are understood too. Thousands separators work as well: 1,000 and 10,000 mean thousands. One catch: a single separator followed by exactly three digits counts as a thousands separator, so 2.125 is read as 2125; type 2.1250 when you mean two and an eighth.
  4. Read the result line, such as 12 in = 30.48 cm. The copy button next to it copies the whole line, units included.
  5. To convert in the opposite direction, press the arrows button between the two unit lists: it swaps the units and keeps your value.

Under the result, a table converts 1, 2, 5, 10, 20, 50, 100 and 1,000 of the source unit at once. It is a quick way to print a small chart for the kitchen or the workshop, or to check several quantities from the same recipe without retyping. The page address keeps your choices, so a bookmarked or shared link reopens on the same conversion.

What you can convert

The converter covers 23 measures, and a conversion is always between two units of the same measure. Turning litres into kilograms or cups of flour into grams is not a unit conversion but a density problem, so those pairs are not offered.

  • Everyday measures: length, area, mass, volume, temperature, time, speed and count (units and dozens).
  • Computing: digital storage from single bits to terabytes, in bits and in bytes.
  • Running and cycling: pace in minutes per kilometre, minutes per mile, seconds per metre and seconds per foot.
  • Science and engineering: pressure (pascal, bar, torr, psi), energy (joule, watt-hour), power, electric current, voltage, frequency (including rpm and radians per second), angle, illuminance (lux, foot-candle), volumetric flow rate and parts per million, billion, trillion and quadrillion.
  • Power systems: reactive power (VAR), apparent power (VA) and reactive energy (VARh), with their kilo, mega and giga multiples.

How the result is calculated

The calculations come from the open-source convert-units library. Every unit is defined as a multiple of a base unit of its system, the metre on the metric side and the foot on the imperial side for length, and the two systems are tied by a fixed ratio. Your value is multiplied up to the base unit, carried across to the other system when needed and divided down to the target unit. Temperature is the exception, because its scales do not share a zero: Celsius to Fahrenheit needs a multiplication and an offset.

result = value × factor(from unit) ÷ factor(to unit) °F = °C × 9/5 + 32

Example 1, length: an inch is defined as 2.54 cm, so 12 in = 12 × 2.54 = 30.48 cm, and 180 cm ÷ 2.54 = 70.86614 in.

Example 2, temperature: 180 °C × 9/5 + 32 = 356 °F, a common oven setting. In the other direction, 0 °F = (0 − 32) × 5/9 = −17.77778 °C. The two scales meet at −40, where −40 °C is also −40 °F.

Example 3, data: a byte has 8 bits, so a download speed of 100 Mb/s moves at most 100 ÷ 8 = 12.5 MB per second. That is why a 100-megabit connection never shows “100” in a download window.

Rounding and how results are displayed

Each result is rounded to 7 significant digits. This is what turns the library's internal 2.5399999187 back into the exact 2.54 cm per inch, and it is more precision than any household or workshop instrument can use. The display then shows at most seven decimal places, so very small results lose digits on screen: 1 mm shows as 0.0393701 in.

Results below 0.000000001 or from 1,000,000,000,000,000 upward switch to scientific notation, for example 1 nanosecond = 3.1688e-17 years. Large whole numbers also lose their last digits: 500 GB converted to bytes shows 536,870,900,000, while the exact value is 536,870,912,000 (500 × 1,024³). When you need an exact count of bytes, multiply it out yourself.

Units that are easy to confuse

  • KB, MB, GB use steps of 1,024. Here 1 GB = 1,024 MB. Drive makers count in steps of 1,000, so a drive sold as 500 GB holds 500,000,000,000 bytes, which converts to 465.6613 GB, the figure Windows shows for such a drive.
  • Bits and bytes. A lowercase b is a bit and an uppercase B a byte: 1 MB = 8 Mb. Internet plans are sold in megabits, files are measured in megabytes.
  • US volumes only. Gallon, quart, pint, cup and fluid ounce are US customary: 1 gal = 3.785412 L. The imperial gallon (4.54609 L) is not in the list.
  • Two kinds of ton. t is the US short ton of 2,000 lb (907.184 kg); mt is the metric tonne of 1,000 kg.
  • Tablespoons differ by country. The US tablespoon (Tbs) is 14.78676 ml; the Swedish msk in the same list is exactly 15 ml. The list also holds the other Swedish kitchen measures: krm (1 ml), tsk (5 ml), kkp (150 ml), glas (200 ml) and kanna (2.617 L).
  • m/h means miles per hour, not metres per hour: 120 km/h = 74.56454 m/h.
  • Foot and US survey foot differ by two parts per million (1 ft-us = 1.000002 ft). Only land surveyors working over long distances need the survey foot.

When to double-check the number

The library stores the pound as 0.453592 kg instead of the legal definition of 0.45359237 kg, so pound and ounce results can be off in the seventh digit: 70 kg shows as 154.3237 lb, while the exact definition gives 154.3236 lb. The knot is in the same situation and shows 1.851999 km/h instead of exactly 1.852. That makes no difference to a recipe, a parcel or a boat trip, but for laboratory, legal or trade measurements, use the official definitions.

The converter does not judge whether a value makes physical sense. It will turn −300 °C into −26.85 K even though nothing can be colder than 0 K. Pace results are decimal minutes rather than minutes and seconds: 5 min/km converts to 8.046746 min/mi, which is about 8 minutes 3 seconds per mile (0.046746 × 60 ≈ 2.8 s). Months and years are averages of 30.4375 and 365.25 days, which suits estimates but not calendar counting.

Frequently Asked Questions

Which measures and units can I convert?
There are 23 measures: length, area, mass, volume, temperature, time, speed, pace, digital storage, pressure, energy, power, current, voltage, frequency, angle, illuminance, volumetric flow rate, parts per (ppm to ppq), count (each and dozen) and three electrical ones used in power engineering (reactive power, apparent power and reactive energy). Each measure has its own list of units, from millimetres and miles to kilowatt-hours, psi and arcseconds.
Why does 1 inch show exactly 2.54 cm?
Because every result is rounded to 7 significant digits. The conversion library stores a few factors with tiny floating-point noise (1 inch comes out as 2.5399999187 cm internally), and rounding to 7 digits gives back the exact defined value of 2.54. Seven digits is far more precision than a tape measure, a kitchen scale or a thermometer can deliver.
Is 1 GB equal to 1,000 MB or 1,024 MB here?
1,024 MB. The digital measure uses binary steps of 1,024 for kilo, mega, giga and tera, for both bytes (KB, MB, GB, TB) and bits (Kb, Mb, Gb, Tb). Disk and memory-card makers use steps of 1,000, so a card sold as 64 GB holds 64,000,000,000 bytes, which this converter shows as about 59.6 GB.
Can I convert UK (imperial) gallons, pints or fluid ounces?
No. The gallon, quart, pint, cup and fluid ounce in the volume list are US customary units: 1 gal = 3.785412 litres. An imperial gallon is 4.54609 litres and an imperial pint 568.261 ml, so for a British recipe or UK fuel figures, convert from litres or millilitres yourself using those numbers instead of picking gal or pnt.
Can I convert litres to kilograms or cups of flour to grams?
Not with this tool, because volume and mass are different measures and the link between them is the density of the substance. A litre of water weighs close to 1 kg, a litre of olive oil about 0.91 kg and a cup of flour much less than a cup of sugar. Convert the volume here, then multiply by the density of what you are measuring.
What is the difference between t and mt in the mass list?
t is the US short ton of 2,000 pounds (907.184 kg) and mt is the metric tonne of 1,000 kg. The British long ton of 2,240 pounds is not in the list. If a document written outside the United States says “ton”, it almost always means the metric tonne.
Can I save or share a conversion?
Yes. Once you change anything, the page address records the measure, both units and the value, for example ?measure=temperature&from=C&to=F&value=180. Bookmark it or send the link and the converter opens on the same conversion.
Are my values sent anywhere?
No. The conversion runs in your browser with the open-source convert-units library that is loaded with the page, so the numbers you type are not sent to a server. After the page has loaded, conversions keep working even if the connection drops.
Why does the converter accept −300 °C or a negative length?
The tool converts numbers and does not check whether a quantity is physically possible. −300 °C converts to −26.85 K, which cannot exist because nothing is colder than absolute zero (0 K, −273.15 °C). Negative values are still useful for differences and for temperatures above absolute zero, such as −40 °C, which is also −40 °F.
Why are month and year conversions not whole numbers of days?
Because they are averages: a month is 30.4375 days and a year is 365.25 days (8,766 hours), the mean length over the leap-year cycle used by the library. They are fine for estimates such as “how many hours in a year”, but to count the days between two real dates use a date calculator instead.

Sources

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