Free Calculators & Unit Converters
Convert anything instantly — length, weight, temperature, volume, speed, data and more. Trusted by millions of users worldwide.
Most Popular Converters
The conversions our users search for most — quick access to the tools you need every day.
Centimeters to Feet & Inches
Convert height measurements between metric and imperial systems instantly.
Kilograms to Pounds
Switch between kg and lbs for weight conversions in fitness, cooking and shipping.
Celsius to Fahrenheit
Convert temperatures between °C and °F for weather, cooking and science.
Miles to Kilometers
Convert distances between miles and kilometres for travel and navigation.
Length & Distance Converters
Convert between metric and imperial length units — millimeters, centimeters, meters, kilometers, inches, feet, yards and miles.
Weight & Mass Converters
Convert grams, kilograms, pounds, ounces, stone, tonnes and more. Perfect for cooking, fitness, shipping and science.
Temperature Converters
Convert between Celsius, Fahrenheit and Kelvin — for weather, cooking, science and everyday use.
Volume & Liquid Converters
Convert liters, gallons, milliliters, fluid ounces, cups, pints and quarts for cooking, science and everyday use.
Area Converters
Convert square feet, square meters, acres, hectares and more — for real estate, construction and land measurement.
More Converters
Speed, data storage, energy, pressure, time, fuel consumption and more — all the unit converters you'll ever need.
Math & Everyday Calculators
Handy calculators for percentages, fractions, age, dates, BMI and more — no conversion needed, just quick answers.
Loan & Mortgage Calculators
Calculate monthly payments, total interest and amortization schedules for mortgages, car loans, personal loans and student loans.
The Fastest Free Unit Converter Online
Welcome to CalcuSwift — your go-to destination for free, fast and reliable unit conversions and online calculators. Whether you need to convert centimeters to feet, switch from Celsius to Fahrenheit, or figure out how many liters are in a gallon, we've built every tool you need in one clean, easy-to-use website.
Our unit converter covers every major measurement category — length and distance, weight and mass, temperature, volume, area, speed, data storage, energy, pressure and time. Each converter works instantly in your browser with no downloads, no sign-up and no cost. We also include handy everyday calculators like percentage calculator, BMI calculator, age calculator and square footage calculator.
Why Use CalcuSwift?
There are plenty of unit converters online, but CalcuSwift is designed to be the fastest and most comprehensive. Every calculator loads instantly, works on mobile and desktop, and gives you results as you type — no clicking "calculate" required. We cover both metric to imperial and imperial to metric conversions, so whether you're in the US, UK, Europe or anywhere else in the world, we've got you covered.
Our length converter handles everything from nanometers to light-years. Our weight converter covers milligrams through to metric tonnes. Our temperature converter supports Celsius, Fahrenheit and Kelvin. And our volume converter handles everything from teaspoons to Olympic swimming pools (yes, really).
Metric vs. Imperial — What's the Difference?
The metric system (used by most of the world) is based on powers of ten, making it very logical and easy to work with. The imperial system (used primarily in the United States) uses units like inches, feet, yards, miles, ounces, pounds and gallons. If you've ever wondered how many feet are in a meter or how many kilograms in a pound, our converters give you the answer instantly — and show you the formula too, so you can understand the maths behind it.
Converting between the two systems comes up all the time in everyday life — when following a recipe from another country, checking your weight on a foreign scale, reading a weather forecast in a different unit, or buying fuel abroad. CalcuSwift makes all of these conversions effortless.
Popular Conversions We Cover
Some of the most searched unit conversions on the internet include kg to lbs, cm to inches, miles to km, Celsius to Fahrenheit, liters to gallons, feet to meters, ounces to grams and stone to kg. We have dedicated, fast-loading pages for every single one of these, plus hundreds more. Our data storage converter handles everything from bits and bytes through to petabytes and exabytes — essential for anyone working in IT or buying cloud storage.
Articles & Guides
Learn the science and history behind units of measurement with our in-depth guides.
Metric vs. Imperial: A Complete Guide to Understanding Both Systems
Why does the US still use miles and pounds while the rest of the world uses kilometers and kilograms? We explore the history, the differences, and when each system is used.
Read article →Understanding Temperature Scales: Celsius, Fahrenheit and Kelvin Explained
From Anders Celsius to Daniel Fahrenheit to Lord Kelvin — the fascinating history of how we measure temperature, and why three different scales still exist today.
Read article →Bytes, Megabytes and Terabytes: How Data Storage Units Actually Work
Is a megabyte 1,000 kilobytes or 1,024? Why do hard drives show less space than advertised? We explain data storage units from bits to exabytes in plain English.
Read article →Cooking Conversions Made Easy: Cups, Grams, Ounces and More
Following a recipe from another country? We break down the most common cooking measurement conversions and explain why volume and weight are not the same thing in baking.
Read article →