UNIT CONVERSION GUIDE
Unit conversion formulas for metric, imperial, and engineering units
Unit conversion changes a measurement into another unit without changing the real quantity. Most categories use a base-unit multiplier, while temperature uses an offset formula because Celsius, Fahrenheit, and Kelvin have different zero points.FORMULA
Converted value = input value × source factor ÷ target factor; °F = °C × 9/5 + 32; °C = (°F − 32) × 5/9WORKED EXAMPLE
If 1 kilometer equals 1000 meters and 1 mile equals 1609.344 meters, then 5 kilometers = 5000 ÷ 1609.344 = 3.10686 miles.STEP BY STEP
Choose the correct conversion family
Length, area, volume, mass, speed, pressure, energy, power, torque, density, angle, frequency, data, and temperature each use their own unit list. Choose the family first so meters are not mixed with seconds or pascals.
Convert through a base unit when possible
Most conversions work by converting the source value to a base unit, then converting from the base unit to the target unit. For example, feet can convert to meters first, then meters can convert to kilometers.
Use special temperature formulas
Temperature conversion is not simple multiplication. Celsius to Fahrenheit adds 32 after scaling, Fahrenheit to Celsius subtracts 32 before scaling, and Kelvin uses an absolute zero offset.
Keep significant digits reasonable
Engineering and science problems often need enough digits to avoid rounding too early. For homework or estimates, round only after the final converted value is calculated.
Check whether the unit is squared or cubed
Area and volume conversions are different from length conversions. If 1 m = 100 cm, then 1 m² = 10,000 cm² and 1 m³ = 1,000,000 cm³.
Use scientific notation for very large or tiny results
Values such as bytes, frequencies, pressures, and densities can become very large or very small. Use scientific or engineering notation when the decimal form becomes hard to read.
Identify the unit family
Choose the correct family first: length, area, volume, mass, temperature, speed, pressure, energy, power, torque, density, data, angle, frequency, force, acceleration, or time.
Convert through the base unit when needed
Many converters first change the input into a base unit, then change that base value into the target unit. For example, kilometers can convert through meters before becoming miles or feet.
Handle temperature separately
Temperature conversion is different because Celsius, Fahrenheit, and Kelvin do not share the same zero point. That is why °F to °C and °C to °F need formulas with +32 or −32.
Check the size of the result
Engineering and scientific problems often produce very large or very small numbers. Use scientific notation or engineering notation when the result is easier to read that way.
Keep the physical meaning consistent
Do not convert between unrelated families. Pressure, torque, energy, and power have different meanings even when their formulas may include related base units.