Unit Converters
Convert temperature, length, weight and volume using exact defined factors, with the formula shown alongside every answer.
Eleven free converters covering everyday metric and imperial units. Every result uses exact defined conversion factors and shows the formula, so you can trust the answer and see how it was calculated.
Converter categories
Each converter below handles one measurement family with the units people actually search for. Pick a category to open its dedicated tool.
Length converter
Convert between metres, kilometres, centimetres, millimetres, miles, yards, feet and inches. Useful for DIY projects, travel distances and construction measurements where plans mix metric and imperial. Open the length converter.
Weight converter
Convert between kilograms, grams, pounds, ounces and stone. Handy for recipes, fitness tracking and shipping quotes that switch between metric and imperial systems. Open the weight converter.
Temperature converter
Convert between Celsius, Fahrenheit and Kelvin. Essential for weather reports, oven settings and science homework, since temperature scales convert with a formula rather than a simple multiplier. Open the temperature converter.
Speed converter
Convert between miles per hour, kilometres per hour, metres per second and knots. Useful when driving abroad, comparing running paces or reading aviation and marine speeds. Open the speed converter.
Volume converter
Convert between litres, millilitres, gallons, quarts, pints, cups and fluid ounces. A lifesaver for recipes, because a US cup and a metric cup are not the same size. Open the volume converter.
Area converter
Convert between square metres, square kilometres, square feet, square yards, acres and hectares. Used for property listings, floor plans and land area where listings vary by country. Open the area converter.
Energy converter
Convert between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTUs. Covers nutrition labels, electricity bills and heating specs in one place. Open the energy converter.
Data storage converter
Convert between bytes, kilobytes, megabytes, gigabytes and terabytes. Useful when comparing file sizes, storage plans and download estimates across devices. Open the data storage converter.
Time unit converter
Convert between seconds, minutes, hours, days and weeks. Handy for project estimates, billing hours and any calculation that mixes time units. Open the time unit converter.
How these converters work
Most unit conversions are a single multiplication. Each unit is defined against a base unit for its category, and converting means dividing by one factor and multiplying by another. Length uses the metre, weight uses the kilogram, and volume uses the litre.
Exact versus approximate factors
Several of the factors used here are exact by definition rather than measured. One inch is exactly 2.54 centimetres, and one pound is exactly 0.45359237 kilograms. These were fixed by international agreement, so conversions between imperial and metric length and weight carry no rounding error beyond what the display shows.
Why temperature is different
Temperature is the exception. Celsius, Fahrenheit and Kelvin do not share a zero point, so converting between them needs an offset as well as a scale factor. That is why the Celsius to Fahrenheit formula is multiply by 9/5 then add 32, rather than a single multiplication. Kelvin starts at absolute zero, which is why it has no negative values.
Significant figures
A converted value should not claim more precision than the measurement you started with. If you measure something as 10 cm, with two significant figures, the honest conversion is 3.9 inches rather than 3.937008 inches. The extra digits are arithmetic, not measurement.
US and UK units are not always the same size
The volume converter lists separate US and UK entries for gallons, pints and fluid ounces because they are genuinely different sizes, not a labeling quirk: a US gallon is about 3.785 litres, while a UK (imperial) gallon is about 4.546 litres, roughly 20% larger. Picking the wrong one silently gives a wrong answer with no error to catch it, so check which one a recipe, tank capacity or shipping spec actually means before converting.
Frequently asked questions
Common Time Questions
Quick answers to the time questions people search for most. Each answer starts with the number, then shows the math behind it.
How many seconds are in a day?
There are 86,400 seconds in a day. A day has 24 hours, each hour has 60 minutes, and each minute has 60 seconds, so 24 × 60 × 60 = 86,400.
| 1 minute | 60 seconds |
| 1 hour | 3,600 seconds |
| 1 day | 86,400 seconds |
| 1 week | 604,800 seconds |
How many minutes are in a day?
There are 1,440 minutes in a day. With 24 hours in a day and 60 minutes in each hour, the math is 24 × 60 = 1,440.
How many hours are in a year?
A common year has 8,760 hours, and a leap year has 8,784 hours. Multiply 365 days by 24 hours to get 8,760. Leap years add one extra day, which adds 24 hours.
How many seconds are in a year?
A common year has 31,536,000 seconds, and a leap year has 31,622,400 seconds. That is 86,400 seconds per day multiplied by 365 days (or 366 in a leap year).
How many weeks are in a year?
A common year has 52 weeks and 1 day; a leap year has 52 weeks and 2 days. Since 365 divided by 7 leaves a remainder of 1, every year spills one weekday into a 53rd partial week.
How many days are in 6 months?
It depends on which months: anywhere from 181 to 184 days. Six months starting in January (non-leap year) total 181 days, while six months starting in July total 184 days, because months range from 28 to 31 days. For deadlines that must be exact, always count calendar days instead of assuming months are equal.
Need to calculate the time between two specific dates? Try our date difference calculator.