Unit Converter — Free, Instant, 60+ Units

One unit converter for length, weight, temperature and five more

This is a free online unit converter that covers 45 units across 8 categories — length, weight, temperature, speed, area, volume, data storage, and time — with both metric and imperial units in the same place. Pick a category pill, choose a From and a To unit, and the result appears instantly as you type; the ⇄ swap button reverses the direction without retyping, and a quick reference table shows what one unit equals across the category. Every conversion runs entirely in your browser — nothing you enter is sent to a server, so there is no upload, no login, and nothing stored.

The value of a converter is only as good as the numbers behind it, so the rest of this page is the honest version: the exact factors and formulas each category uses, why data storage counts in 1024s, and the handful of places where a general converter genuinely can’t help.

The exact factors and formulas each category uses

Seven of the eight categories convert by scaling to a single base unit, so results are exact ratios of the stored factors. Temperature is the exception — its scales have offsets, so it uses formulas instead of a multiplier. These are the relations the tool applies internally:

So to convert kg to lbs the tool divides by 0.45359237 (giving 1 kg = 2.20462 lb), and to convert km to miles it divides 1000 by 1609.344 (giving 1 km = 0.621371 mi) — the same constants you would use by hand.

How every conversion is computed

For length, weight, speed, area, volume, data and time, the converter multiplies your value by the From unit’s base factor, then divides by the To unit’s base factor. Temperature can’t work that way because the scales don’t share a zero point, so it first converts your value to Celsius and then out to the target — which is why converting Celsius to Fahrenheit gives an exact result no matter which pair you pick:

5 miles  ->  kilometres
  5 x 1609.344 m   = 8046.72 m
  8046.72 / 1000   = 8.04672 km

100 C  ->  Fahrenheit and Kelvin
  100 x 9/5 + 32   = 212 F
  100 + 273.15     = 373.15 K

Results are shown to up to 8 significant figures, and the tool switches to scientific notation for values that reach a trillion or drop below 0.0001 — so a tiny milligram-to-tonne answer stays readable instead of collapsing to a row of zeros. A few limits are worth knowing up front: the Time category treats a month as a fixed 30 days and a year as a fixed 365 days (no leap-year handling), and the Volume category uses US customary gallons, cups and fluid ounces rather than UK imperial ones. Those are design choices, not bugs, but they change the numbers.

Data storage: why 1 GB here is 1024 MB, not 1000

Convert GB to MB in this tool and you get 1024, not 1000 — because the Data category uses the binary (power-of-two) convention. That’s the same math Windows File Explorer uses when it reports file and drive sizes. Standards bodies define the decimal units differently and reserve separate names — KiB, MiB, GiB (kibibyte, mebibyte, gibibyte) — for the 1024-based values:

This is exactly why a hard drive sold as “1 TB” shows up as roughly 931 GB in Windows: the manufacturer counted 1,000,000,000,000 bytes in decimal, and the operating system divides by 1024s. Because this converter also divides by 1024s, its GB and MB results match what your computer reports — not the number printed on the drive’s box.

Common conversion mistakes

Assuming the gallon is imperial

The Volume category uses the US gallon (3.78541 L). A UK imperial gallon is about 4.546 L — roughly 20% larger — so a US-based result will read low if you meant imperial. The same gap applies to cups and fluid ounces.

Expecting 1 GB to equal 1000 MB

Here it’s 1024 MB, matching your operating system. If you specifically need the decimal (marketing) value drive makers quote, multiply by 1000 instead of using the Data category.

Treating months and years as exact

Time conversions use a fixed 30-day month and 365-day year. That’s fine for a quick estimate, but don’t use it to count exact calendar spans, billing periods, or anything that touches February or a leap year.

Converting cups to grams for a recipe

A cup is a unit of volume and a gram is a unit of mass. Turning one into the other depends on the ingredient’s density — 1 cup of flour and 1 cup of honey weigh very different amounts — which no general unit converter can know.

Reading the reference table as the whole category

The quick reference table shows the first five units of the active category in a 5×5 grid. Categories with more than five units (like Length or Time) still convert every unit in the dropdowns — the table is a scale-at-a-glance summary, not the full list.

What this converter doesn’t cover

This is a physical-quantity converter, so a few common conversions sit outside its eight categories on purpose. It doesn’t handle money — exchange rates change by the second, so use the dedicated currency converter for that. It also skips fuel economy (mpg to L/100 km is a reciprocal relationship, not a linear factor), pressure, energy, power and angle. And because mass-to-volume conversions need an ingredient’s density, cooking swaps between grams and cups aren’t something a units tool can do reliably. For everything that is a clean ratio of standard units — metric to imperial length, weight, temperature, speed, area, volume, data storage and time — this is the fast, private, no-login option.

Frequently asked questions