Unit Converter

Since 2019, all SI units are defined by fixed values of fundamental constants — meter from the speed of light, kilogram from Planck constant. US customary units are defined by exact conversions to SI: 1 inch = 0.0254 m exactly, 1 pound = 0.45359237 kg exactly. So most unit conversions in this tool are mathematically exact within rounding.

Exceptions: temperature is offset-and-scale (°F to °C is not a simple multiplier); fluid ounces differ between US (29.5735 mL) and Imperial (28.4131 mL); the gallon is the most-confused unit in the English-speaking world (US gallon 3.78541 L vs Imperial gallon 4.54609 L — the US one is smaller).

• Length — fully linear. 1 mile = 1609.344 m exactly. Nautical mile = 1852 m exactly. Surveying uses "US survey foot" (slightly different from international foot) — only relevant for land surveying.
• Mass / weight — kg, lb, oz, stone (UK 14 lb). Mass and weight conflated in everyday use; in physics, mass is invariant, weight depends on gravity (you weigh less on the Moon).
• Temperature — not linear. °C = (°F − 32) × 5/9. Kelvin is offset from Celsius (K = °C + 273.15). Always use the absolute scale (K) when ratios matter.
• Volume — US fluid oz ≠ Imperial fluid oz ≠ US dry pint ≠ liquid pint. The conversion category needs to know which system.
• Speed — most conversions linear. Mach number depends on temperature and altitude (speed of sound varies); treating "Mach 1" as a fixed mph is a common mistake.
• Pressure — psi, kPa, bar, atm, mmHg, inHg. 1 atm = 101325 Pa exactly. Gauge pressure vs absolute pressure is a separate axis (psi-g vs psi-a) that matters in engineering.
• Energy — joule (SI), calorie (food calories are actually kilocalories, 1 kcal = 4184 J), BTU, electron-volt. Food labeling kcal vs SI kJ on European labels is the most-encountered conversion in daily life.
• Data — bytes / kibibytes (KiB, 1024) / kilobytes (KB, 1000). Storage manufacturers use 1000 (so a "1 TB" disk is 1,000,000,000,000 bytes); RAM and most file managers use 1024. The difference grows: 1 TiB - 1 TB = 99 GB.

• You are reading a US recipe and need to bake from a European kitchen — convert cups, ounces, and Fahrenheit oven temperature without doing the arithmetic.
• You are reading scientific literature and need to translate cgs units to SI (1 erg = 1e-7 J, 1 gauss = 0.0001 T) before plugging into a modern equation.
• You inherited an engineering spec in mixed units (drawing in mm, fasteners in inches, fluid in gallons) and need a clean SI equivalent.
• You are travelling and want to convert km/h speed limits, °C weather forecasts, and L/100km fuel economy without doing mental arithmetic.

• It will not handle compound units (specific heat in J/(kg·K), torque in N·m). Each is its own category in a comprehensive unit library (UnitsNet, Pint); this tool covers common conversions, not arbitrary dimensional analysis.
• It will not handle currency. Currency conversion is a different problem — rates change in real time and the conversion is not algebraic. Use a separate currency tool.
• It will not convert "approximate" units. "A handful" is not a unit. "Room temperature" is approximately 20°C but varies by region and season. The tool converts well-defined units only.