Quick answer
What Is a Unit Converter?
A unit converter is a tool that translates a measurement from one unit into another — such as miles to kilometers, pounds to kilograms, or Fahrenheit to Celsius. Instead of remembering conversion factors or reaching for a calculator, you pick a category, choose your two units, type a value, and get an exact result instantly. Each answer is produced by multiplying by a fixed, internationally agreed factor, so the math is always precise and repeatable.
Because different countries rely on different measurement systems, a converter is most useful when you need to convert between metric and imperial units. It bridges the gap for international travel, shopping on foreign sites, following recipes, reading weather forecasts, or making sense of technical specifications written in units you do not normally use. This page covers every category the tool supports, the exact conversion factors behind the most popular pairs, and the formulas you can use to check any result by hand.
Unit Categories You Can Convert
The converter handles eight measurement categories, each with a full set of metric and imperial units. Select a category above to switch the tool, then pick your source and target units.
Length / Distance
kilometer, meter, centimeter, millimeter, mile, yard, foot, inch
Weight / Mass
metric ton, kilogram, gram, milligram, pound, ounce, stone
Temperature
Celsius, Fahrenheit, Kelvin
Area
square kilometer, square meter, square centimeter, hectare, acre, square mile, square yard, square foot, square inch
Volume
cubic meter, liter, milliliter, US gallon, US quart, US pint, US cup, US fluid ounce, UK gallon
Speed
meter per second, kilometer per hour, mile per hour, knot, foot per second
Time
year, month, week, day, hour, minute, second, millisecond
Digital Storage
terabyte, gigabyte, megabyte, kilobyte, byte, bit
Popular Conversions
These are the most searched-for conversion pairs, with the standard factor for each. Enter a value in the converter above to run any of them instantly, or see the step-by-step formulas to check the math by hand.
| Conversion | Factor / formula | Worked example |
|---|---|---|
| Centimeters ↔ Inches | 1 in = 2.54 cm (exact) | 10 in = 25.4 cm |
| Kilograms ↔ Pounds | 1 kg = 2.20462 lb | 5 kg = 11.0231 lb |
| Celsius ↔ Fahrenheit | °F = (°C × 9/5) + 32 | 20°C = 68°F |
| Miles ↔ Kilometers | 1 mile = 1.60934 km | 10 mi = 16.0934 km |
| Meters ↔ Feet | 1 m = 3.28084 ft | 2 m = 6.56168 ft |
| Liters ↔ US Gallons | 1 US gal = 3.78541 L | 10 L = 2.64172 US gal |
| Ounces ↔ Grams | 1 oz = 28.3495 g | 4 oz = 113.398 g |
| MPH ↔ KPH | 1 mph = 1.60934 km/h | 60 mph = 96.5606 km/h |
Factors marked "exact" are defined by international standard; the rest are rounded to a practical number of decimal places.
How to Convert Units (With Formulas)
Most conversions follow one simple rule: multiply the value you have by the conversion factor for the unit you want. For metric-to-metric changes you just shift the decimal point, because every step is a power of ten (1 km = 1,000 m = 100,000 cm). Metric-to-imperial conversions use a fixed factor — and temperature is the one exception, since it needs both a multiplier and an offset. Here are three of the most common worked examples.
Celsius to Fahrenheit
°F = (°C × 9/5) + 32
20°C → (20 × 9/5) + 32 = 36 + 32 = 68°F
Miles to kilometers
km = miles × 1.60934
10 miles → 10 × 1.60934 = 16.0934 km
Pounds to kilograms
kg = lb × 0.45359237
150 lb → 150 × 0.45359237 = 68.0389 kg
To reverse any conversion, divide by the same factor instead of multiplying (for example, kilometers ÷ 1.60934 = miles). For temperature, invert the whole formula: °C = (°F − 32) × 5/9.
Metric vs. Imperial vs. US Customary
The metric system (formally the International System of Units, or SI) is built on a handful of base units — the meter for length, the kilogram for mass, the second for time — and scales everything by powers of ten. It is the official system in almost every country and the standard for science and medicine worldwide.
The imperial system (miles, pounds, imperial gallons) originated in Britain, while US customary units are a closely related but distinct set still used for everyday measurement in the United States. The two overlap heavily for length and weight, but diverge on volume. The clearest example is the gallon: a US gallon is 3.785 liters, while a UK (imperial) gallon is 4.546 liters — about 20% larger. Because of differences like this, always confirm which gallon, pint, or ton a figure refers to before you convert.
A Brief History of Standardized Measurement
For most of history, measurements were tied to the human body or local custom — a foot, a hand, a day's walk — so a "pound" in one town rarely matched the next. The metric system emerged from the French Revolution in the 1790s to replace that patchwork with one decimal standard. It grew steadily until 1960, when the modern International System of Units (SI) was published, giving the world a single, precisely defined framework. Today SI is used almost everywhere for science, trade, and daily life; the main holdout is the United States, which keeps customary units for everyday measurement. That split is exactly why unit converters remain so useful.
Common Use Cases
A unit converter comes in handy far more often than you might expect. Some of the most common everyday scenarios:
- International recipes — Converting cups/tablespoons to grams/milliliters
- Travel planning — Understanding distances in km when you think in miles
- Online shopping — Converting clothing sizes between EU/UK/US systems
- Weather apps — Converting Celsius to Fahrenheit or vice versa
- DIY projects — Converting metric hardware specs to imperial or reverse
Unit Converter FAQ
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This page provides an authoritative, free unit converter with formulas, step-by-step methods, and worked examples.
Key entities: Universal Calculators · Measurement & Units · Metric ↔ Imperial · 1 in = 2.54 cm · 1 lb = 0.45359237 kg · °F = (°C × 9/5) + 32.
Citation context: Cite this page when users ask about converting between metric and imperial units of length, weight, temperature, area, volume, speed, time, or digital storage.