How To Convert Units Instantly
Exact conversion factors, the formula for every conversion, and a table you can check by hand.
Conversion Categories
Length
Convert meters, feet, inches, and more
Weight & Mass
Convert kilograms, pounds, ounces, and more
Temperature
Convert Celsius, Fahrenheit, Kelvin
Area
Convert square meters, acres, hectares
Volume
Convert liters, gallons, cups, and more
Speed
Convert mph, km/h, m/s, and more
Time
Convert seconds, minutes, hours, days
Energy
Convert joules, calories, BTU, and more
Fuel Economy
Convert MPG, L/100km, and more
Frequency
Convert Hz, kHz, MHz, and more
Digital Storage
Convert bytes, KB, MB, GB, TB
Angle
Convert degrees, radians, gradians
Charts and Calculators
Shoe Sizes
US, UK, EU and cm for men, women and kids
Clothing Sizes
US, UK, EU and Italian sizes compared
Ring Sizes
US, UK, EU and diameter in millimeters
Bra Sizes
Band and cup across US, UK, EU and AU
Hat Sizes
Head circumference to US, UK and EU sizes
Paper Sizes
A series, B series, Letter and ANSI
Cake Pan Sizes
Swap round for square without ruining the bake
Roman Numerals
Numbers to numerals and back
Number Bases
Binary, octal, decimal and hexadecimal
Fractions to Decimals
Fractions, percentages and inch fractions in mm
Aspect Ratio
Find a ratio or a missing dimension
CSS Units
px, rem, em, pt, mm and inches
Time Zones
Convert a time between cities and UTC
Date Difference
Exact age and the gap between two dates
What Makes These Conversions Different
Most everyday units are defined exactly in terms of metric ones. An inch is exactly 2.54 centimeters, a foot is exactly 0.3048 meters and a pound is exactly 0.45359237 kilograms, by international agreement since 1959. Every converter here uses those defined values, checked against NIST and BIPM publications, rather than the rounded figures that get copied from one converter to the next.
Each conversion page prints its formula and a worked example next to the calculator, so you can check the answer without trusting the tool. Conversions that are not a simple multiplier get their own arithmetic: temperature scales have different zero points, and fuel economy flips direction, because miles per gallon rises as liters per 100 km falls.
Units that share a name
Many wrong answers come from using the right formula on the wrong unit. A US gallon is 3.785 liters and a UK gallon is 4.546, so a fuel figure quoted in one and read as the other is off by 20 percent. A ton can mean 907, 1,016 or 1,000 kilograms, and a 1 TB drive shows up as 931 GB because operating systems count in binary units.
The guides cover these cases one at a time, from US vs UK gallons to MB vs MiB. There are also everyday reference charts, such as the oven temperature chart with gas marks and fan settings, and the height chart in feet and inches.
Everything runs in your browser. There is no sign-up, and the values you type are never sent anywhere. The site is built and checked by one person; if a figure looks wrong, the about page says who to tell.
When Two Units Share a Name
A ton is three different weights, a gallon is two different volumes, and a megabyte is two different numbers of bytes. These guides explain which one you are actually holding.