Free Unit Converter (Length, Weight & Temperature)
Free unit converter. Convert length (mm, cm, m, km, in, ft, yd, mi), weight (mg, g, kg, t, oz, lb), and temperature (°C, °F, K) into every unit at once from a single input.
Length conversion base values (1 unit = how many meters)
| Unit | Base value |
|---|---|
| Millimeter (mm) | 1 mm = 0.001 m |
| Centimeter (cm) | 1 cm = 0.01 m |
| Meter (m) | 1 m = 1 m |
| Kilometer (km) | 1 km = 1,000 m |
| Inch (in) | 1 in = 0.0254 m |
| Foot (ft) | 1 ft = 0.3048 m |
| Yard (yd) | 1 yd = 0.9144 m |
| Mile (mi) | 1 mi = 1,609.344 m |
Weight conversion base values (1 unit = how many kilograms)
| Unit | Base value |
|---|---|
| Milligram (mg) | 1 mg = 0.000001 kg |
| Gram (g) | 1 g = 0.001 kg |
| Kilogram (kg) | 1 kg = 1 kg |
| Metric ton (t) | 1 t = 1,000 kg |
| Ounce (oz) | 1 oz = 0.028349523125 kg |
| Pound (lb) | 1 lb = 0.45359237 kg |
Temperature conversion formulas
| Celsius to Fahrenheit | °F = °C × 9/5 + 32 |
|---|---|
| Fahrenheit to Celsius | °C = (°F − 32) × 5/9 |
| Celsius to Kelvin | K = °C + 273.15 |
What is a unit converter? Metric vs. imperial at a glance
This unit converter lets you turn a single number into every related unit at once across three everyday categories: length, weight, and temperature. Instead of multiplying by a ratio on a calculator or hunting through a conversion chart, you enter one value and its unit, and every other unit in that category updates instantly — whether you're turning centimeters into inches or pounds into kilograms.
Length and weight convert with a simple ratio through a common base unit (meters and kilograms), so multiplying by a fixed factor is enough. Temperature is different: Celsius, Fahrenheit, and Kelvin each place their zero point somewhere else, so a plain ratio won't work and a dedicated formula is required instead. For imperial units like inches, feet, pounds, and ounces, this tool uses the exact definitions fixed by the 1959 international yard-and-pound agreement, so the results are precise enough for schoolwork, professional use, or everyday reference.
How to use the unit converter
- Pick a category Choose length, weight, or temperature depending on what kind of value you want to convert.
- Enter your value Type the number you want to convert. Decimals are supported.
- Select the source unit Choose the unit your value is currently in — centimeters, kilograms, Celsius, and so on.
- Read every converted result All other units in that category are converted and listed automatically — no button to press.
- Convert another value right away Change the number or unit and the results refresh instantly, so you can check several values in a row.
Tips for getting more out of it
- Enter one value and pick its unit — every other unit in that category is converted at the same time, so there's no need to look them up one by one.
- Length and weight units convert with a simple ratio, but Celsius, Fahrenheit, and Kelvin each have a different zero point, so temperature can't be converted with a plain ratio.
- Inches, feet, yards, miles, ounces, and pounds have their metric equivalents precisely defined by the 1959 international yard-and-pound agreement, and this tool uses those exact definitions.
- Handy when you need to convert units from foreign recipes (ounces, Fahrenheit) or overseas DIY plans and books (inches, feet).
Common ways to use this unit converter
Making sense of weather and body-weight readings abroad
When traveling somewhere that uses Fahrenheit and pounds, quickly translate a forecast or a bathroom scale reading into the Celsius and kilograms you're used to.
Converting foreign recipe quantities and oven temperatures
Many recipes list ingredient amounts in ounces and oven heat in Fahrenheit; convert them to grams and Celsius before you start cooking.
Checking DIY plans and imported furniture dimensions
Imported tools, furniture, and blueprints are often labeled in inches and feet — convert to centimeters or meters to compare against your own space.
Homework and exam prep for science and physics
Use it to check your own arithmetic when converting between Celsius, Fahrenheit, and Kelvin, or between metric and imperial units.
Estimating overseas shipments and product weights
When a product page lists weight in pounds or ounces, convert it to kilograms to get a realistic sense of shipping cost and how heavy the package will feel.
Unit conversion glossary
- Metric system
- A measurement system built on the meter, kilogram, and second, with units related to each other by powers of ten. It is the official system in most countries worldwide.
- Imperial / US customary system
- A system that includes inches, feet, yards, miles, ounces, and pounds, still widely used in everyday life in the United States. The ratios between units are not decimal, so converting requires fixed conversion factors.
- International yard and pound agreement
- A 1959 agreement among the US, UK, and other English-speaking countries that fixed 1 inch at exactly 2.54 centimeters and 1 pound at exactly 0.45359237 kilograms. This tool uses those same definitions.
- Celsius (°C)
- A temperature scale where water freezes at 0 degrees and boils at 100 degrees. It is used in everyday life in most countries, including Japan.
- Fahrenheit (°F)
- A temperature scale where water freezes at 32 degrees and boils at 212 degrees, used in everyday life in the United States. Each degree is a smaller step than a degree Celsius, allowing finer-grained temperature readings.
- Kelvin (K)
- The SI base unit of temperature, anchored at absolute zero (0 K). Each step is the same size as a degree Celsius, and it is the standard unit used in scientific calculations.
- Absolute zero
- The theoretical lower limit of temperature, below which nothing can exist, equal to about -273.15°C. This tool treats any input below this value as invalid.
- Conversion factor
- A fixed number you multiply by to turn one unit into another. For example, the conversion factor from inches to meters is 0.0254.
Frequently Asked Questions
Side Note — The stories behind the meter and the degree Fahrenheit
Today's meter has been defined, since 1983, as the distance light travels in a vacuum in 1/299,792,458 of a second. But the original meter, defined in 1791 by scientists during the French Revolution, was one ten-millionth of the distance from the North Pole to the equator along a meridian. Basing a unit on the Earth itself was a revolutionary attempt to end the chaos of measurements that had varied by region and were often tied to a local ruler's own body (a "foot" literally meaning the length of someone's foot).
Fahrenheit (°F) was devised around 1724 by the German physicist Daniel Gabriel Fahrenheit. He originally set 0 degrees at the freezing point of a brine solution (ice, water, and ammonium chloride) and roughly 96 degrees at human body temperature. More precise later measurements redefined the scale so that water freezes at 32 degrees and boils at 212 degrees, giving us the Fahrenheit scale used today. Because each degree Fahrenheit is a smaller step than a degree Celsius, it can express everyday temperature changes in finer detail, which is one reason it remains in everyday use in the United States.
Many imperial units trace back to everyday body parts and objects from medieval Europe. A "foot" is literally the length of a human foot; a "yard" is thought to derive from the distance from a person's nose to an outstretched hand, or from a standard length used for measuring cloth; and a "mile" comes from the Latin mille passus, meaning a thousand paces marched by Roman soldiers. Where the metric system pursued a universal, reproducible standard, imperial units grew organically out of the everyday human scale — a striking contrast between the two systems.