Unit Converter — Length, Weight, Temperature & More
Convert between units of length, mass, temperature, digital storage and time. Each result shows the factor used, so you can see where the number comes from.
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What this tool does
This converter moves a value between units in five categories: length, mass, temperature, digital storage and time. It reads the unit definitions, performs the conversion and reports both the result and the factor that produced it, so the number is explained rather than simply asserted. Temperatures are distinguished because they need more than a multiplier.
Method
Each category names a base unit — the metre, the kilogram, the degree Celsius, the byte or the
second — and every unit carries a factor against that base. Converting multiplies the value by
the source unit’s factor and divides it by the target unit’s, as in value × from ÷ to.
Temperature cannot work this way because its scales do not share a zero, so the value is taken to
Celsius first and then to the target scale, which applies the offset between them. Digital storage
is where the two prefix systems meet: decimal SI prefixes step by powers of 1000, while binary IEC
prefixes step by powers of 1024, so a kilobyte and a kibibyte are deliberately different values.
Example
| Input | Result |
|---|---|
1000 m | 1 km |
1 mi | 1.609344 km |
100 °C | 212 °F |
Why unit conversion goes wrong
A conversion is a multiplication by a defined factor, so the arithmetic is trivial. The failures come from three places: the wrong unit being selected, an ambiguous unit name, and round-tripping through a rounded value.
| Ambiguity | Why it matters |
|---|---|
oz — mass or fluid volume? | An ounce of weight and a fluid ounce are different quantities with different factors |
ton — short, long or metric? | 2,000 lb, 2,240 lb and 1,000 kg are three different tons |
gallon — US or imperial? | 3.785 L versus 4.546 L, a 20% difference |
MB — 106 or 220? | Decimal megabytes versus binary mebibytes, a 5% difference |
| temperature | Not a simple factor: the scales have different zero points |
This tool names both the unit and its system where an ambiguity exists, so the selection is explicit rather than inferred from an abbreviation.
Temperature is not like the others
Most conversions are value × factor. Temperature needs an offset as well, because the
scales do not share a zero: 0 °C is 32 °F and 273.15 K. Converting 20 °C is not
twenty times a factor. The tool applies the full affine transform in both directions, which is
why a temperature conversion that looks right at freezing can be badly wrong at room temperature
in a naive implementation.
Precision and rounding
The factors are exact definitions where they exist — an inch is exactly 25.4 mm, a pound exactly 0.45359237 kg — and the output is rounded for display, not for calculation. Round-tripping a rounded display value reintroduces error: converting 1 mile to 1.61 km and back gives slightly less than a mile. For a chain of conversions, use the exact factor rather than the displayed number.
Significant figures
A conversion cannot create precision. Converting 1.0 km (two significant figures) to metres gives 1000 m arithmetically, but the input only justified 1.0 × 103 m. The tool shows the arithmetic result; deciding how many digits are meaningful is a judgement about the input, and it is not one a converter can make for you.
Frequently asked questions
Can I convert weight to volume?
Not without a density. A gram is a mass and a millilitre is a volume; the bridge between them is the substance’s density, and it differs for flour, water, oil and sugar. A recipe that says “one cup of flour” cannot be converted to grams without knowing which flour and how it was packed. This converter deliberately does not guess a density; use a cooking reference for the specific ingredient.
Which categories are supported?
Length, mass, temperature, digital storage and time. Those are the five where the factors are exact and the conversions are unambiguous. Volume, area, speed and energy are not included yet; adding them means adding exact factors and a test per unit, not just a menu entry, which is why the list grows slowly and deliberately.
Why is a US gallon different from an imperial gallon?
They are different units with the same name: a US liquid gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, about 20% larger. The same split applies to fluid ounces and pints. Since volume is not currently a category here, the practical rule is to check which gallon a recipe or a specification means before converting it with any tool.
Why is a pound of feathers not a pound of gold?
Because troy and avoirdupois pounds differ: the everyday pound is 0.45359237 kg, while the troy pound is 0.3732417216 kg. Precious metals are quoted in troy ounces (31.1034768 g), not the 28.349523125 g avoirdupois ounce. The mass converter here uses the avoirdupois pound; for bullion, use the troy figure explicitly.
How is each conversion calculated?
Every non-temperature unit is defined as a factor against its category base unit: length and mass use the metre and the kilogram, digital storage uses the byte, and time uses the second. A value is multiplied by the source factor and divided by the target factor, so the arithmetic is exact rather than a chain of rounded steps.
Why is temperature treated differently?
Celsius, Fahrenheit and Kelvin do not share a common zero, so a multiplier alone is not enough. The value is first converted to Celsius and then to the target scale, which handles the offset as well as the size difference between degrees.
What is the difference between KB and KiB?
A kilobyte (KB) is 1000 bytes, following the decimal SI prefix. A kibibyte (KiB) is 1024 bytes, following the binary IEC prefix. The same distinction separates MB from MiB and GB from GiB, and it is the usual reason a drive’s advertised capacity differs from what the operating system reports.
How precise are the results?
Factors are stored at full double precision and only the displayed value is rounded, to at most six decimal places with more shown for very small numbers. The 1 mile to 1.609344 kilometres result, for example, is the exact legal definition.
Is anything sent to a server?
No. All categories, factors and arithmetic ship with the page and run in your browser; the numbers you enter never leave the device.
Go deeper
Longer explanations of the problems this tool solves:
Sources
- BIPM, The International System of Units (SI Brochure), 9th edition — base units and SI prefixes.
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI) — unit conversions and factors.
- IEC 80000-13, Quantities and units — Part 13: Information science and technology — binary prefixes such as KiB and MiB.
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