Unit Converter
Convert between 200+ units across 10 categories: length, weight, temperature, area, volume, speed, data, time, pressure, and energy. Runs entirely in your browser.
How to Use
This free online unit converter handles over 200 units across 10 measurement categories. Every calculation runs locally in your browser with zero network requests, so conversions are instantaneous and fully private. Here is how to use it:
- Select a category from the tabs at the top: Length, Weight, Temperature, Area, Volume, Speed, Data, Time, Pressure, or Energy. Each tab shows only the units relevant to that measurement type.
- Choose your source unit from the "From" dropdown and enter a numeric value. The converter accepts integers, decimals, and negative numbers (useful for temperature).
- Choose your target unit from the "To" dropdown. The converted result appears immediately as you type, with no button click required.
- Use the swap button (the arrow icon between the two columns) to instantly reverse the direction of conversion. Your current value stays, and the result recalculates automatically.
The formula bar below the converter shows the exact conversion ratio for 1 unit, making it easy to verify results or do mental math. A quick reference table at the bottom lists common conversions for each category so you can look up everyday values at a glance. Related tools include the Temperature Converter for more temperature scales and the Percentage Calculator for ratio math.
About This Tool
Unit conversion is the process of expressing a quantity in a different unit of measurement while preserving the same magnitude. Two measurement systems dominate global use: the International System of Units (SI), commonly called the metric system, and the imperial/US customary system still used in the United States, Liberia, and Myanmar for everyday purposes.
The Metric System (SI)
Formalized in 1960, SI defines seven base units: the meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). All other metric units derive from these through powers of 10, making conversions within SI straightforward: 1 kilometer equals exactly 1,000 meters, and 1 milligram equals exactly 0.001 grams. This decimal structure is why SI is the universal standard in science, engineering, and medicine.
Imperial and US Customary Units
The imperial system evolved from English units codified by the British Weights and Measures Act of 1824. US customary units diverged from imperial before that standardization, which is why a US gallon (3.785 liters) differs from an imperial gallon (4.546 liters). Cross-system conversions require precise conversion factors. For instance, 1 inch is defined as exactly 25.4 millimeters, and 1 pound equals exactly 0.45359237 kilograms.
Temperature Scales
Temperature is unique among physical quantities because its scales are not related by simple multiplication. Celsius and Fahrenheit use different zero points and degree sizes: the formula F = C x 9/5 + 32 involves both scaling and offsetting. The Kelvin scale starts at absolute zero (-273.15 degrees Celsius), where molecular motion theoretically ceases. One kelvin equals one degree Celsius in magnitude, but Kelvin has no negative values and is the SI base unit for thermodynamic calculations.
Digital Storage Units
Digital storage has two competing conventions. Decimal prefixes (KB, MB, GB) use powers of 1,000, following SI conventions adopted by hard drive manufacturers and network standards. Binary prefixes (KiB, MiB, GiB) use powers of 1,024, matching how RAM and file systems actually address memory. The difference matters: 1 TB (decimal) equals 931.32 GiB (binary), which is why a "1 TB" hard drive shows roughly 931 GB in your operating system. See the Base64 Encoder for data encoding conversions.
Why Use This Tool
Unit conversion is a fundamental task in dozens of disciplines. Here are the most common reasons people reach for a converter:
- Engineering and manufacturing require exact conversions between metric and imperial. A tolerance specified as 0.05 mm must be correctly expressed as 0.00197 inches for US machine shops. Material specifications, pressure ratings, and torque values all cross system boundaries regularly.
- Cooking and nutrition demand volume and weight conversions when following recipes from different countries. A European recipe calling for 250 mL of milk needs to become roughly 1.06 US cups. Nutritional labels may show energy in kilojoules (Australia, EU) or kilocalories (US), requiring a 4.184:1 conversion factor.
- Science education relies on unit conversion as a core skill. Students converting between SI prefixes, cgs units, and imperial measures develop dimensional analysis ability that underlies all quantitative reasoning.
- International travel means encountering unfamiliar measurement systems daily. Speed limits in km/h versus mph, fuel economy in liters per 100 km versus miles per gallon, and weather forecasts in Celsius versus Fahrenheit all require quick mental or digital conversion.
- Software development involves data size calculations where the difference between decimal and binary prefixes can cause bugs. Cloud storage pricing in GB versus GiB, network bandwidth in Mbps, and file size limits all depend on precise unit understanding. Related: the Date Calculator handles time-based conversions, and the Math Evaluator supports inline unit conversions in expressions.