Unit Converter: 160 Units Across 31 Physical Dimensions

Convert between 160 units across 31 physical dimensions, with dimension-mismatched conversions made impossible.

Most unit converters are a flat list of factors, which is why they happily turn kilograms into kilometres if you click the wrong row. This one is organised by physical dimension first: you pick length, mass, pressure, energy or one of the other dimensions, and only units belonging to that dimension are offered. A conversion that would be dimensionally meaningless is not a mistake you can make here, because the interface never presents it.

How to convert units with the dimension picker

Choose a dimension first — Length, Mass, Temperature, Data Size or any of the other 31.
Pick the From and To units; only units of that dimension are listed, and the swap button reverses the pair.
Type the value to convert. The result appears immediately, rounded to ten significant digits for display.
Press Copy result to copy the full-precision number without thousands separators, or copy the page URL to share the exact conversion.

Why dimensions come before units

Every unit in the converter is defined by a factor relative to one base unit of its dimension. Converting means going through that base: your input is multiplied into the base unit, then divided out into the target. Doing it this way means a new unit needs exactly one number to be correct against every other unit in its dimension, rather than a hand-written pair for each combination. Those factors come from the mathjs unit system, with the few units it lacks — calories, knots, nautical miles, the radiation and viscosity units — registered on top in terms of units mathjs already defines.

It also makes the round trip honest. Convert 1 mile to nanometres and back and you land on 1 mile again, because both directions use the same single factor rather than two separately rounded constants. The dimension list covers the everyday ones (length, mass, time, area, volume, speed) and the engineering ones (pressure, energy, power, force, acceleration), with metric, imperial, US customary and a few domain-specific units such as nautical miles, mils, grains, stone and BTU.

Everyday unit conversions and their factors

Centimeters and inches: 1 in = 2.54 cm exactly, so divide centimeters by 2.54.
Kilograms and pounds: 1 lb = 0.45359237 kg exactly, or about 2.2046 lb per kilogram.
Celsius and Fahrenheit: °F = °C × 9/5 + 32, which puts 100 °C at 212 °F.
Kilometers and miles: 1 mi = 1.609344 km exactly.
Liters and US gallons: 1 gal = 3.785411784 L.
PSI and bar: 1 psi ≈ 0.0689476 bar, so a 32 psi tire is about 2.2 bar.
Kilowatt-hours and BTU: 1 kWh ≈ 3,412.14 BTU.

All 31 unit dimensions and their units

Mechanics (12): length (nanometers to miles, plus nautical miles and mils), mass (milligrams to metric tons, grains, ounces, pounds, stone, US short tons), time (nanoseconds to centuries), speed (including knots), acceleration (including standard gravity), area (including hectares and acres), volume (milliliters to cubic feet, with US kitchen measures), force, torque, pressure, energy and power.
Fluids (2): dynamic viscosity in pascal-seconds, poise and centipoise; kinematic viscosity in m²/s, stokes and centistokes.
Radiation (3): absorbed dose in grays and rad, equivalent dose in sieverts and rem, radioactivity in becquerels and curies.
Digital (2): data size from bits to exabytes plus the binary KiB, MiB, GiB and TiB; data rate from bits per second to gigabits per second, plus B/s and MB/s.
Electrical (7): current, charge (coulombs, mAh, Ah), voltage, resistance, capacitance, inductance and magnetic flux density (tesla and gauss).
Other (5): temperature (°C, °F, K, °R), angle (degrees, radians, gradians, arcminutes, arcseconds), frequency (Hz to GHz), luminous intensity (millicandela to kilocandela) and amount of substance (millimoles and moles).
Across all 31 dimensions the menus list 160 units.

Temperature is the exception, and it is handled properly

Celsius, Fahrenheit and Kelvin are not related by a simple multiplication — they are affine, meaning each conversion needs an offset as well as a scale. A converter that treats them like every other unit produces the classic bug where 0 °C becomes 0 °F.

Temperature conversions here apply the offset explicitly, so 0 °C is 32 °F and −40 lands on −40 in both scales. Kelvin and Rankine are included for absolute-temperature work.

Metric, imperial and US customary units in this converter

SI, the modern metric system, builds every unit from seven base units such as the meter, kilogram and second, scaled by powers of ten. Imperial (British) and US customary units share many names but not always the same size, and that is where conversions go wrong: a US gallon is 3.785 L while an imperial gallon is 4.546 L, and a US fluid ounce is 29.57 mL against 28.41 mL for the imperial one.

The volume list here uses the US customary definitions for fluid ounces, cups, pints, quarts and gallons; imperial volumes are not offered, so convert a UK recipe through milliliters instead. Mass keeps the two tons apart: the metric ton is 1,000 kg and the US short ton is 2,000 lb, or 907.18 kg. The 1,016 kg British long ton is not listed.

Reading results you can trust

Results are shown to ten significant digits and then trimmed, so floating-point noise like 3.5000000000000004 never reaches the screen. Values too small for decimal notation switch to exponential form instead of collapsing to zero — 1 electronvolt reads as 1.602176634e-19 J, not as "0 J", which is the failure mode that makes a converter quietly untrustworthy.

Large values are grouped for readability. If you are copying a figure into a spreadsheet or a calculation, strip the separators or copy from the result field directly.

Working offline and sharing a conversion

The whole factor table ships with the page, so once it has loaded there is no network request for any conversion — it keeps working on a plane, on a locked-down corporate network, or with the tab left open after your connection drops. Nothing you type is transmitted anywhere.

The current dimension, source unit, target unit and value are kept in the page URL, so a converted figure can be bookmarked or pasted into a ticket and the recipient sees exactly the conversion you did, not a blank converter.

Where a converter is the wrong tool

Currency: exchange rates change by the minute and are not physical constants, so they are deliberately absent rather than shipped stale.
Units that depend on material or context, such as converting a volume of flour to a weight, need a density you supply — a generic converter guessing one would be wrong more often than right.
Regulatory or billing figures should be checked against the rounding rules of the standard you are filing under; this tool rounds for display, not to a legal specification.
Very large or very small magnitudes are exact to double-precision arithmetic, which is roughly fifteen significant digits — enough for engineering work, not for arbitrary-precision metrology.

Questions people ask about Universal Unit & Dimensional Converter

Why can't I convert kilograms to litres?: They belong to different dimensions: kilograms measure mass and litres measure volume. Converting between them requires the density of the specific substance, which the converter has no way to know. Pick the dimension you are actually working in, or multiply by a density you trust yourself.
Does the converter round my value before converting?: No. The arithmetic runs at full double precision on the number you typed, and rounding happens only when the result is displayed. That is why converting a value out and back returns the original figure rather than drifting a little each time.
Which pressure and energy units are supported?: Pressure includes pascals, kilopascals, bar, millibar, atmospheres, PSI, torr and millimetres of mercury. Energy covers joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and electronvolts, so both laboratory and utility-bill figures are covered in one place.
Is anything I type sent to a server?: Nothing. The conversion table is part of the page itself and every calculation happens in your browser, so no value, file or unit selection leaves the device. You can verify that by opening your browser's network panel while converting, or by disconnecting entirely and continuing to use the page.
How do I convert within a dimension the list does not include?: If the dimension is missing entirely, the converter cannot help and you should treat that as out of scope rather than forcing a related unit. If a specific unit is missing from a dimension that exists, converting through a shared unit you both know — for example going via metres or via joules — gives the same answer the tool would.
How do I convert Celsius to Fahrenheit?: Multiply the Celsius value by 9/5 and add 32, so 37 °C becomes 98.6 °F. In the converter, choose the Temperature dimension, set Celsius to Fahrenheit and type the value; the offset is applied for you, which a plain multiply-only converter gets wrong.
Does it convert data storage units like GB and GiB?: Yes. Data Size includes decimal units (kB, MB, GB, TB, PB, EB, powers of 1,000) and binary ones (KiB, MiB, GiB, TiB, powers of 1,024). One gigabyte equals about 0.9313 gibibytes, the gap behind a new drive showing less space than its label.

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Content reviewed 2026-09-27.