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
Formules de Conversion
Formules mathématiques et équations derrière les conversions d'unités avec exemples résolus.
Temperature Formules de Conversion
CalculatorCelsius 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
K = C + 273.15
Example: 25°C = 25 + 273.15 = 298.15 K
Kelvin to Celsius
C = K - 273.15
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 Formules de Conversion
CalculatorMeters to Feet
ft = m × 3.28084
Example: 10 m = 10 × 3.28084 = 32.81 ft
Feet to Meters
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
cm = in × 2.54
Example: 12 in = 12 × 2.54 = 30.48 cm
Weight & Mass Formules de Conversion
CalculatorKilograms 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 Formules de Conversion
CalculatorLiters 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 Formules de Conversion
Calculatormph to km/h
km/h = mph × 1.60934
Example: 60 mph = 60 × 1.60934 = 96.56 km/h
km/h to m/s
m/s = km/h × 0.27778
Example: 100 km/h = 100 × 0.27778 = 27.78 m/s
Knots to km/h
km/h = knots × 1.852
Example: 30 knots = 30 × 1.852 = 55.56 km/h
Pressure Formules de Conversion
CalculatorPascal to Bar
bar = Pa × 0.00001
Example: 101325 Pa = 101325 × 0.00001 = 1.013 bar
PSI to Pascal
Pa = PSI × 6894.76
Example: 14.7 PSI = 14.7 × 6894.76 = 101325 Pa
ATM to Pascal
Pa = atm × 101325
Example: 1 atm = 1 × 101325 = 101325 Pa
Energy Formules de Conversion
CalculatorJoules to Calories
cal = J × 0.239006
Example: 1000 J = 1000 × 0.239006 = 239.01 cal
kWh to Joules
J = kWh × 3,600,000
Example: 1 kWh = 1 × 3,600,000 = 3,600,000 J
BTU to Joules
J = BTU × 1055.06
Example: 100 BTU = 100 × 1055.06 = 105,506 J
Power Formules de Conversion
CalculatorWatts to Horsepower
hp = W × 0.001341
Example: 746 W = 746 × 0.001341 = 1.0 hp
Horsepower to Watts
W = hp × 745.7
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.
FAQ sur les Formules
Common questions about conversion formulas and equations.
What is a conversion factor?
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.
Why is temperature conversion different from other units?
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.
What are SI base units?
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.
How do I derive a conversion formula?
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.
Are these formulas exact or approximate?
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.