Unit Converter

Related Calculators

Conversion Categories Supported

The exact unit list appears inside each category in the calculator. Keeping categories separate prevents invalid conversions such as trying to convert kilograms directly to meters.

Metric, SI and US Customary Units

The International System of Units (SI) provides a globally standardized framework for measurement. Everyday use can still involve non-SI units such as miles, feet and pounds, particularly in the United States and in specific industries.

A unit converter bridges these systems by applying a defined factor or formula. The BIPM publishes the authoritative SI Brochure describing the International System of Units. BIPM SI Brochure.

Length and Distance Conversion Examples

Some factors, such as 1 inch = 2.54 cm, are exact definitions. Displayed decimal rounding should still match the precision needed for the task.

Weight Converter and Mass Conversion Examples

In everyday language “weight” and “mass” are often used interchangeably, but physics distinguishes them. Most consumer conversion tools use “weight” as the familiar label for mass-unit conversions.

Temperature Conversion Formulas

Temperature is different from simple factor conversions because Celsius and Fahrenheit have different zero points. Kelvin also uses an offset from Celsius.

Area and Volume Conversions

Area units are squared, so their factors are not the same as the underlying length factors. Volume units are cubed or defined by capacity relationships. For example, converting meters to feet uses a linear factor, while square meters to square feet uses the square of that relationship.

This is why manually reusing a length factor for area or volume can be wrong. Select the correct category and let the converter use the correct dimensional relationship.

Speed, Time and Angle Conversions

Speed combines distance and time, while time and angle each have their own conventional units. Converting 60 miles per hour to kilometers per hour requires the mile-to-kilometer factor while keeping the hour consistent. Angle conversions commonly use the relation between degrees and radians.

Data, Pressure, Energy and Power

Technical conversions can involve unit systems with domain-specific conventions. Digital data, for example, may use decimal or binary prefixes depending on context. Pressure, energy and power can also have several common units used in engineering, science and industry.

When a conversion is being used for a specification, engineering drawing or regulated process, confirm the expected unit standard and required precision rather than relying only on a rounded display value.

Precision, Significant Figures and Rounding

A converter can display many decimal places even when the original measurement is rough. More digits do not automatically mean more accuracy. If a measurement is known only to three significant figures, reporting ten significant figures after conversion creates false precision.

Keep enough internal precision to avoid rounding error, then round the final converted value to match the quality of the source measurement and the requirements of the task.

Common Unit Conversion Mistakes

• Converting between incompatible quantities.
• Using a length factor for area or volume.
• Mixing kilograms and pounds in a health calculator.
• Using a simple multiplier for Celsius/Fahrenheit instead of the offset formula.
• Confusing decimal data prefixes with binary prefixes.
• Rounding too early or reporting false precision.
• Copying the right number with the wrong unit label.

Always keep the unit symbol attached to the value while checking your work. A correct number paired with the wrong unit is still a wrong answer.

Exact Conversions, Approximate Conversions and Significant Digits

Some unit relationships are defined exactly, while others are used with a practical conversion factor. Even when the conversion factor is exact, the original measurement may not be. Converting “2.0” of a measured quantity into ten decimal places does not create new measurement accuracy.

Keep enough digits for the calculation, then round the final result to a precision appropriate for the source. This matters in engineering, laboratory work, construction and any task where a rounded input can propagate through later calculations.

Temperature deserves extra attention because Celsius and Fahrenheit require an offset as well as a scale factor. They cannot be converted correctly by multiplying by one constant alone.

Dimensional Analysis: A Reliable Way to Check Unit Conversion

Dimensional analysis treats unit labels as part of the calculation. To convert 5 kilometers to meters, multiply by a ratio equal to one: 5 km × (1000 m / 1 km) = 5000 m. The kilometer units cancel, leaving meters.

This method is especially useful when several conversions are chained together because an uncancelled unit reveals where the setup went wrong. Area and volume conversions also become clearer: if a length factor is squared for area or cubed for volume, the unit factor must be squared or cubed too.

Use the converter for speed, then use dimensional analysis as a quick independent check whenever the stakes or precision requirements are high.

Common Length and Distance Conversions

Common Mass and Weight Conversions

Everyday language often calls kilograms and pounds units of “weight,” although in physics kilograms measure mass while weight is a force. For ordinary conversion tasks, the familiar relationships are still useful.

Why Area and Volume Factors Are Different

If 1 meter = 100 centimeters, then 1 square meter is 100² = 10,000 square centimeters and 1 cubic meter is 100³ = 1,000,000 cubic centimeters. The conversion factor must be squared for area and cubed for volume.

This is why using a linear factor on an area or volume value can create an error of hundreds or thousands of times.

Speed and Rate Conversions

Speed contains both distance and time units, so both parts of the unit matter. Converting kilometers per hour to meters per second requires converting kilometers to meters and hours to seconds.

For compound units such as fuel economy, density or pressure, convert each dimension in the correct direction.

SI Prefixes: kilo, centi, milli, micro and More

Prefix capitalization matters: m usually means milli, while M means mega.

Data Units: Decimal and Binary Conventions

Computer-storage units can be confusing because decimal and binary conventions have both been used. In SI usage, 1 kB = 1000 bytes and 1 MB = 1,000,000 bytes. Binary multiples are formally named kibibyte (KiB = 1024 bytes) and mebibyte (MiB = 1,048,576 bytes).

When comparing storage, memory or transfer rates, check which convention the source uses instead of assuming every “KB” or “MB” means the same factor.

Angles: Degrees and Radians

A full circle is 360 degrees or 2π radians, so the conversion follows directly from that equality.

For trigonometric calculations after converting an angle, make sure the Scientific Calculator uses the matching angle mode.

Significant Figures and Measurement Uncertainty

A conversion can be mathematically exact while the original measurement is not. Converting 12.3 cm to 4.842519… inches does not mean the physical measurement is known to six decimal places. Preserve enough digits during the conversion, then round the result to a precision appropriate for the source measurement and purpose.

Frequently Asked Questions