Unit Converter

Length, weight, and temperature

Length and weight convert through a fixed base unit (meters and kilograms), so any pair — millimeters to miles, ounces to kilograms — comes out accurate. Temperature uses the actual Celsius/Fahrenheit/Kelvin formulas rather than a simple ratio, since it doesn't scale from zero the same way: 0°C is 32°F, not 0°F, which trips up a straight-multiplication approach.

Units covered

Length: millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. Weight: milligrams, grams, kilograms, ounces, pounds, and stone. Temperature: Celsius, Fahrenheit, and Kelvin. Switch the category dropdown to see the full unit list for each — every conversion recalculates instantly as the value or either unit changes.

Mass vs. weight, and why it rarely matters here

Strictly, kilograms and pounds measure mass while "weight" technically means the force of gravity on that mass — a distinction that matters in physics but not for anything this tool is used for, since everyday conversions (a recipe, a shipping label, a body weight reading) are always comparing the same quantity under the same gravity. This converter treats "weight" and "mass" units interchangeably for that reason, matching how the units are actually used day to day.

Common conversions people forget

A few conversions come up often enough to be worth having memorized rather than looked up each time: 1 inch is exactly 2.54cm, 1 mile is about 1.609km, 1kg is about 2.205lb, and body temperature of 98.6°F is 37°C. Where accuracy actually matters — cooking, medication dosing, engineering measurements — it's worth running the exact figure through this converter rather than relying on a rounded rule of thumb, since small rounding errors compound in anything multiplied or scaled up.

Why stone still shows up as a weight unit

Stone (14 pounds) is included here mainly for readers in the UK and Ireland, where body weight is still commonly reported in stone rather than kilograms or pounds in everyday conversation, even though the metric system is otherwise standard — a holdover from imperial units that never fully migrated for this one specific measurement. Someone weighing "11 stone 4" is about 71.7kg or 158lb, a conversion that trips people up specifically because stone is almost never used for anything other than body weight.

Fahrenheit, Celsius, and where each is standard

Celsius is the global standard for weather, cooking, and science almost everywhere except the United States, which still uses Fahrenheit for everyday temperature despite using metric units for most scientific and medical contexts. Kelvin, meanwhile, is used almost exclusively in scientific contexts (it's Celsius shifted so 0K is absolute zero, with no negative values), which is why it's included here for completeness but rarely needed for everyday conversions.