Online Unit Converter & Conversion Calculators

Need to convert between units quickly and accurately? Our free online unit converter tools let you switch between hundreds of units across nine categories — from energy and power to pressure, temperature, and volume — without reaching for a formula sheet or doing the math by hand. Whether you’re an engineer double-checking a spec, a student working through a problem set, or just trying to figure out how many liters are in a gallon, these calculators give you an instant, accurate answer.

Each conversion calculator below works the same simple way: enter a number, pick your starting unit, choose the unit you want to convert to, and get your result immediately.

Conversion calculators available on this page:

• Energy unit converter — convert between joules, BTU, calories, kilowatt-hours, therms, and dozens of other energy units.
• Energy & power calculator — see how energy, time, and power relate, with real-world comparisons like gasoline, batteries, and steam.
• Diffusivity converter — convert diffusivity and kinematic viscosity units, including stokes, cm²/s, and ft²/s.
• Force converter — convert between newtons, pounds-force, dynes, kiloponds, and more.
• Mass converter — convert between grams, kilograms, pounds, stones, tons, and other mass units.
• Power converter — convert between watts, kilowatts, horsepower, BTU/hour, and more.
• Pressure converter — convert between pascals, PSI, bar, atmospheres, and other pressure units.
• Temperature converter — convert between Celsius, Fahrenheit, Kelvin, and Rankine.
• Viscosity converter — convert between poise, pascal-seconds, centipoise, and other viscosity units.
• Volume converter — convert between liters, gallons, cubic feet, barrels, and dozens of other volume units.

Bookmark this page to keep every conversion calculator you need in one place, and check back — we’re always looking to add more unit converters based on what our visitors are looking for.