A conversion factor is a multiplier that transforms one unit into another: Linear: target = source \u00d7 factor Non-linear: temperature uses addition too Factors are ratios: 1 m = 3.28084 ft \u2192 factor = 3.28084 7 SI base units: Meter (m) \u2014 length Kilogram (kg) \u2014 mass Second (s) \u2014 time Ampere (A) \u2014 electric current Kelvin (K) \u2014 temperature Mole (mol) \u2014 amount Candela (cd) \u2014 luminous intensity Identify source and target units Find the conversion factor between them Multiply (or apply the formula for temperature) Check: does the result make sense? For chain conversions, multiply factors together Understand the mathematics behind unit conversions. Each formula below shows the exact equation used to convert between units, along with a worked example. Whether you are a student learning dimensional analysis or an engineer double-checking a conversion, these formulas provide the mathematical foundation. How factors are sourced, how the library is updated, and how IEEE 754 rounding is treated are documented on the About page . Converters for these formulas Use the published pair calculators that match the equations on this page. Celsius to Fahrenheit Fahrenheit to Celsius millimeters to inches inches to centimeters kilograms to pounds liters to gallons gallons to liters cups to milliliters milliliters to cups miles per hour to kilometers per hour PSI to kilopascals horsepower to kilowatts kilowatts to horsepower watts to horsepower kilowatt-hours to gigajoules gigajoules to kilowatt-hours radians to degrees centimeters to inches miles to kilometers meters to yards yards to meters grams to ounces pounds to kilograms Temperature Conversion Formulas Celsius to Fahrenheit F = C × 9/5 + 32 Example: 25°C = 25 × 9/5 + 32 = 77°F Fahrenheit to Celsius C = (F - 32) × 5/9 Example: 77°F = (77 - 32) × 5/9 = 25°C Celsius to Kelvin Example: 25°C = 25 + 273.15 = 298.15 K Kelvin to Celsius Example: 300 K = 300 - 273.15 = 26.85°C Fahrenheit to Kelvin K = (F - 32) × 5/9 + 273.15 Example: 212°F = (212 - 32) × 5/9 + 273.15 = 373.15 K Length Conversion Formulas ft = m × 3.28084 Example: 10 m = 10 × 3.28084 = 32.81 ft m = ft × 0.3048 Example: 100 ft = 100 × 0.3048 = 30.48 m Miles to Kilometers km = mi × 1.60934 Example: 5 mi = 5 × 1.60934 = 8.05 km Inches to Centimeters Example: 12 in = 12 × 2.54 = 30.48 cm Weight & Mass Conversion Formulas Kilograms to Pounds lb = kg × 2.20462 Example: 70 kg = 70 × 2.20462 = 154.32 lb Pounds to Kilograms kg = lb × 0.45359 Example: 150 lb = 150 × 0.45359 = 68.04 kg Ounces to Grams g = oz × 28.3495 Example: 8 oz = 8 × 28.3495 = 226.80 g Volume Conversion Formulas Liters to US Gallons gal = L × 0.264172 Example: 10 L = 10 × 0.264172 = 2.64 gal US Cups to Milliliters mL = cups × 236.588

Example: 2 cups = 2 × 236.588 = 473.18 mL US Fluid Ounces to Milliliters mL = fl oz × 29.5735 Example: 8 fl oz = 8 × 29.5735 = 236.59 mL Speed Conversion Formulas km/h = mph × 1.60934 Example: 60 mph = 60 × 1.60934 = 96.56 km/h m/s = km/h × 0.27778 Example: 100 km/h = 100 × 0.27778 = 27.78 m/s km/h = knots × 1.852 Example: 30 knots = 30 × 1.852 = 55.56 km/h Pressure Conversion Formulas bar = Pa × 0.00001 Example: 101325 Pa = 101325 × 0.00001 = 1.013 bar Pa = PSI × 6894.76 Example: 14.7 PSI = 14.7 × 6894.76 = 101325 Pa Pa = atm × 101325 Example: 1 atm = 1 × 101325 = 101325 Pa Energy Conversion Formulas Joules to Calories cal = J × 0.239006 Example: 1000 J = 1000 × 0.239006 = 239.01 cal J = kWh × 3,600,000 Example: 1 kWh = 1 × 3,600,000 = 3,600,000 J J = BTU × 1055.06 Example: 100 BTU = 100 × 1055.06 = 105,506 J Power Conversion Formulas Watts to Horsepower hp = W × 0.001341 Example: 746 W = 746 × 0.001341 = 1.0 hp Horsepower to Watts Example: 2 hp = 2 × 745.7 = 1491.4 W kW to Horsepower hp = kW × 1.341 Example: 100 kW = 100 × 1.341 = 134.1 hp The Mathematics Behind Conversion Linear Conversions Most unit conversions are linear \u2014 you simply multiply by a conversion factor. For example, to convert meters to feet, multiply by 3.28084. The general formula is: target = source \u00d7 (toFactor / fromFactor) Non-Linear Conversions Temperature is the main exception. Because Celsius, Fahrenheit, and Kelvin have different zero points, conversion requires both multiplication and addition. For example: \u00b0F = \u00b0C \u00d7 9/5 + 32 Dimensional Analysis For complex conversions, use dimensional analysis: write each conversion as a fraction where the units cancel. For example, converting miles per hour to meters per second: mph \u00d7 (1609.34 m/mi) \u00d7 (1 hr/3600 s) = m/s All Category Formulas Visit each category page for complete formula references and interactive calculators. Common questions about conversion formulas and equations. A conversion factor is a ratio that expresses how many of one unit equals another unit. For example, 1 meter = 3.28084 feet, so the conversion factor from meters to feet is 3.28084. To convert, multiply your value by the conversion factor. Most conversions are simple multiplication, except temperature which uses addition and subtraction. Temperature scales have different zero points. Celsius and Fahrenheit don't share a common zero — 0°C equals 32°F, not 0°F. This means temperature conversion requires both multiplication and addition/subtraction (e.g., F = C × 9/5 + 32), unlike length or weight which are purely multiplicative. The International System of Units (SI) defines 7 base units: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). All other units are derived from these seven. Use dimensional analysis: write the known relationship between units, then set up a ratio. For example, since 1 inch = 2.54 cm, to convert inches to cm: multiply by 2.54/1. For chain conversions (e.g., miles to meters), multiply successive conversion factors: miles × 5280 ft/mile × 0.3048 m/ft. Some conversions are defined exactly (1 inch = 2.54 cm exactly, 1 foot = 0.3048 m exactly). Others are measured values rounded for practical use (1 mile ≈ 1.60934 km). Temperature conversions between Celsius and Kelvin are exact (K = C + 273.15). We indicate precision in our worked examples. Converters for these formulas Use the published pair calculators that match the equations on this page. Popular pair converters Celsius to Fahrenheit Fahrenheit to Celsius millimeters to inches inches to centimeters kilograms to pounds liters to gallons gallons to liters cups to milliliters milliliters to cups miles per hour to kilometers per hour PSI to kilopascals horsepower to kilowatts kilowatts to horsepower watts to horsepower kilowatt-hours to gigajoules gigajoules to kilowatt-hours radians to degrees centimeters to inches miles to kilometers meters to yards yards to meters grams to ounces pounds to kilograms conversion charts Learn and reference conversion tutorials conversion articles conversion charts conversion cheat sheets sources and precision