Unit Converter Length, Weight, Temperature, Area, Volume, Speed, and Time

What this converter does

This tool expresses the same physical quantity in a different unit of measurement. You enter a value, choose the category, select the unit the value is currently in, and select the unit you want it expressed in. The converter applies the standard factor for that pair of units and returns the equivalent value. It also shows the formula it used, so you can check the arithmetic, and it lists the same value in every other unit of the same category so you can see the scale.

Seven categories are supported. Length and distance covers millimetres through nautical miles. Weight and mass covers milligrams through metric tonnes and imperial stones. Temperature is handled with its own three-scale formulas. Area covers square metres through hectares and acres. Volume covers millilitres through US gallons and imperial gallons. Speed covers metres per second through knots. Time covers seconds through years on a calendar scale.

Everything runs inside the browser. The conversion factors are stored in the page, the arithmetic runs locally, and nothing is transmitted to a server. If the AI insight button is pressed, only an anonymous summary of the category, the number of decimal places in the result, and whether the two selected units belong to the same family is sent to a small serverless function that runs once and then stops. The actual values, units, and results are never included.

How the conversion factors work

For length, weight, area, volume, speed, and time, every unit is defined as a fixed multiple of a single base unit. Length is defined in metres, weight in kilograms, area in square metres, volume in litres, speed in metres per second, and time in seconds. Converting from one unit to another is a two-step operation: multiply the input value by the source factor to express it in the base unit, then divide by the destination factor to express it in the destination unit.

The formula for a given pair of units is simple: output equals input multiplied by the source factor, then divided by the destination factor. For example, converting miles to kilometres means multiplying by 1609.344 and then dividing by 1000, which is the same as multiplying by 1.609344. Converting pounds to kilograms means multiplying by 0.45359237 and dividing by 1, which leaves the multiplier unchanged.

Temperature is the exception. Celsius, Fahrenheit, and Kelvin have different zero points, so a single scale factor is not enough. Celsius to Fahrenheit requires multiply by 9, divide by 5, then add 32. Fahrenheit to Celsius reverses the process. Kelvin is an absolute scale that starts at absolute zero, which corresponds to -273.15 degrees Celsius, so converting between Kelvin and Celsius adds or subtracts 273.15 depending on direction. The converter handles all six directions with the correct formula for each.

Length and distance

Length is the most common conversion category, and it appears in travel, construction, clothing, sports, schoolwork, and online shopping. The converter supports millimetres, centimetres, metres, kilometres, inches, feet, yards, miles, and nautical miles. The metric units are powers of ten apart, so they are easier to convert mentally: one metre is one hundred centimetres, one kilometre is one thousand metres. The imperial units use fixed relationships that are worth memorising: twelve inches in a foot, three feet in a yard, and 5280 feet in a statute mile. A nautical mile is a separate unit that equals exactly 1852 metres and is used in aviation and marine navigation.

When you are converting a distance, be clear about what you are measuring. A straight-line distance between two points is a single length. A perimeter around a room is a sum of lengths and is still measured in metres or feet. An area is the product of two lengths and is measured in square metres or square feet, which is a separate category. Keeping those three apart will save you from the most common unit mistake, which is confusing length with area.

Weight and mass

In everyday language the words weight and mass are used interchangeably, and this converter follows that convention. Strictly speaking, mass is the amount of matter in an object and is measured in kilograms, grams, or pounds-mass. Weight is the force that gravity exerts on that mass and is measured in newtons. On Earth the two are proportional, which is why the everyday interchange works. On the Moon or in orbit the mass stays the same but the weight changes. For cooking, shipping, luggage, fitness, and product comparison, mass is what you actually want, and that is what this tool converts.

The converter supports milligrams, grams, kilograms, metric tonnes, ounces, pounds, and stones. Stones are still used informally in the United Kingdom and Ireland to describe body weight, and one stone equals fourteen pounds. Metric tonnes are widely used in freight, agriculture, and industry, and one tonne equals one thousand kilograms. If you are mixing a metric measurement with an imperial one in the same calculation, convert both to the same base unit first to avoid an accidental factor-of-a-thousand error.

Temperature

Temperature is the only category in this tool that uses a formula with an offset rather than a simple scale factor. Three scales are supported. Celsius sets zero at the freezing point of water and one hundred at the boiling point at standard pressure. Fahrenheit sets thirty-two at the freezing point of water and two hundred and twelve at the boiling point, which gives a finer step between degrees. Kelvin is an absolute scale that starts at absolute zero and uses the same degree size as Celsius.

Two useful reference points are worth remembering. Normal human body temperature is about 37 degrees Celsius, which is 98.6 degrees Fahrenheit. A comfortable room temperature is about 20 to 22 degrees Celsius, which is 68 to 72 degrees Fahrenheit. Water freezes at 0 degrees Celsius, 32 degrees Fahrenheit, and 273.15 Kelvin. The conversion between Celsius and Fahrenheit is not linear in the sense that doubling the Celsius value does not double the Fahrenheit value, because of the offset.

Area and volume

Area measures a two-dimensional surface and is expressed in square units. The converter supports square metres, square kilometres, square centimetres, square feet, square yards, hectares, and acres. The metric area units are powers of ten apart in two dimensions, which means the factor between square metres and square kilometres is one million, not one thousand. A hectare is ten thousand square metres and is a common unit for land. An acre is about 4046.86 square metres, and one hectare is about 2.471 acres.

Volume measures three-dimensional space and is expressed in cubic units or in units of liquid capacity. The converter supports millilitres, litres, cubic metres, US gallons, US quarts, US pints, US cups, US fluid ounces, and imperial gallons. The US gallon is about 3.785 litres, while the imperial gallon is about 4.546 litres, which is a difference of roughly twenty per cent. Recipes from the United States and the United Kingdom are not directly comparable unless you know which gallon is being used, and this tool labels the US gallon explicitly.

Speed and time

Speed expresses distance divided by time and is measured in metres per second, kilometres per hour, miles per hour, feet per second, and knots. The knot is a nautical mile per hour and is used in aviation and marine navigation; one knot equals about 0.5144 metres per second, or about 1.852 kilometres per hour. A road speed limit in kilometres per hour is not the same as the same number in miles per hour; the ratio is about 1.609, so 100 km/h is about 62 mph.

Time is expressed in seconds, minutes, hours, days, weeks, months, and years. Months and years are not fixed intervals. A calendar month ranges from 28 to 31 days, and a calendar year is 365 or 366 days depending on leap years. For practical conversions, this tool uses the average month of about 30.44 days and the average year of about 365.25 days, which are the values used in interest and growth calculations. If you need an exact calendar duration, work with days and count the actual days between the two dates.

Metric and imperial units

Metric units are based on decimal relationships and are the standard in scientific work and in most countries. The International System of Units, or SI, defines seven base units and a set of prefixes that scale those units by powers of ten. Kilo means one thousand, milli means one thousandth, and centi means one hundredth. Because the prefixes are consistent, metric conversions are simple and the arithmetic is easy to check mentally.

Imperial and US customary units remain common in the United States and appear in international product listings, recipes, travel information, and older reference materials. The names can look similar between the two systems while the underlying definitions differ. A US gallon is smaller than an imperial gallon, a US pint is smaller than an imperial pint, and a US fluid ounce is smaller than an imperial fluid ounce. The foot, inch, and pound are the same in both systems by historical agreement. When you are working across systems, always confirm which version of a unit is being used before you trust the conversion.

Common mistakes

Confusing length with area. A metre and a square metre are different quantities and cannot be converted into each other. If a page asks for the area of a room, use square metres or square feet, not metres or feet.

Mixing up US and imperial gallons. A recipe from the United States and a recipe from the United Kingdom use different gallons. The difference is significant enough to change the outcome of a bake or a fuel-economy comparison.

Forgetting the offset in temperature. Doubling a Celsius value does not double the Fahrenheit value, because the two scales have different zero points. Use the formula, not a ratio.

Rounding too early. If the answer feeds into a second calculation, keep the unrounded value. Rounding to the nearest whole number in the middle of a chain of conversions can add up to a visible error at the end.

Assuming a month is thirty days. A calendar month ranges from 28 to 31 days. If you need an exact calendar duration, use days and count the actual interval between the two dates.

Trusting a nominal size. A product listed as ten inches may be a nominal size, not an exact measurement. Where the measurement matters, use a specification from the manufacturer rather than a rounded label on a box.

Mixing units inside one calculation. If one part of a calculation is in metres and another is in feet, convert both to the same unit first. Unit mismatches are the most common source of errors in engineering, construction, and physics coursework.

Where this tool stops

This converter uses standard conversion factors and displays a practical number of decimal places. It does not verify the units you selected against the quantity you actually measured, and it does not know whether a measurement labelled as ten inches is a nominal size or an exact one. It does not model density, so it cannot convert between mass and volume without additional information. It does not handle currency, which changes daily, or units that are specific to a trade or a region without a published conversion factor.

For engineering, medicine, regulated trade, laboratory work, or legal documents, confirm the result against the applicable standard and keep the unrounded value. Some industries define customary units differently, and a manufacturer may publish a nominal size rather than an exact physical measurement. The numbers this tool produces are accurate for the factors it uses, but the responsibility for a measurement that affects safety, money, or compliance belongs to the person applying it.

What the tool does give you is a fast, transparent, private way to convert a measurement, see the formula, and view the same value in every related unit. It is a practical starting point for travel, cooking, shopping, schoolwork, and everyday planning, and it is a useful sanity check on any conversion you have done by hand.