Conversion
Unit Converter
Convert between units of length, weight, volume, speed, and area instantly. Select a category, enter a value, and see all conversions at once. No sign-up required.
All Length Conversions
Most Common Unit Conversions
| From | To |
|---|---|
| 1 mile | 1.60934 km |
| 1 kg | 2.20462 lbs |
| 1 liter | 0.26417 US gal |
| 1 m/s | 3.6 km/h |
| 1 foot | 0.3048 m |
| 1 acre | 4,047 m² |
The Metric vs. Imperial System
The metric system (SI) is used by most of the world. It is base-10: 1 kilometer = 1,000 meters, 1 kilogram = 1,000 grams. This makes calculations straightforward, just move the decimal point.
The imperial system is used primarily in the United States and, for some measures, the United Kingdom. It uses less intuitive ratios: 1 mile = 5,280 feet, 1 pound = 16 ounces. Converting between the two requires fixed multipliers.
Science, medicine, and international trade use metric universally. Everyday life in the US still uses imperial for speed (mph), distance (miles), and weight (lbs). This converter handles both, so you can work in whichever system you need.
How the Conversion Engine Works
Every unit in each category is defined by a single number: how many base units it equals. Length's base unit is the meter, so a mile is stored as 1609.344 (meters), a foot as 0.3048, and a millimeter as 0.001. Converting between any two units in a category is a two-step process: multiply the input by the source unit's factor to get the base-unit value, then divide by the target unit's factor.
This base-unit approach means adding a new unit only requires one conversion factor rather than a separate formula for every possible pair, and it guarantees consistency. Converting miles directly to feet produces the same result as converting miles to meters and then meters to feet, since both paths pass through the same base value.
Results are displayed with up to 6 significant digits and no trailing zeros, which keeps very small values (like 0.0001 acres) and very large ones (like distances in millimeters) both readable without excessive decimal noise.
Speed is a slightly special case because it mixes distance and time units (meters per second, kilometers per hour), but the same base-value logic still applies: meters per second is the base unit, and km/h, mph, knots, and feet/second are each stored as how many meters per second they equal. A car doing 100 km/h, for example, is stored internally as roughly 27.78 m/s before being displayed back out in whichever unit you choose.
What Each Category Covers
Switch between the five categories using the tabs above the converter. Each category has its own base unit and its own list of common units, covering both metric and imperial/US customary systems so you rarely need to leave the tool to find a specific unit.
Length
Meter, kilometer, centimeter, millimeter, mile, yard, foot, inch, and nautical mile. Base unit: meter.
Weight
Kilogram, gram, milligram, pound, ounce, metric ton, and stone. Base unit: kilogram.
Volume
Liter, milliliter, cubic meter, US gallon, quart, pint, cup, fluid ounce, tablespoon, and teaspoon. Base unit: liter.
Speed
Meters/second, km/h, mph, knots, and feet/second. Base unit: meters per second.
Area
Square meter, square kilometer, square mile, acre, hectare, square foot, square yard, and square inch. Base unit: square meter.
Weight and area follow the same pattern: kilogram-based units cover metric mass (kilogram, gram, milligram, metric ton) alongside imperial mass (pound, ounce, stone), while area units span both small metric plots (square meter) and large-scale land measures (hectare, acre, square kilometer, square mile) used in real estate and agriculture.