Reference · 18 formulas
Formula Library
Every formula behind our converters and calculators — with worked examples, variable definitions and links to the matching tool.
Temperature
Celsius to Fahrenheit Formula
Convert any temperature in degrees Celsius to Fahrenheit using a simple linear formula.
°F = °C × 9/5 + 32
Fahrenheit to Celsius Formula
Convert any Fahrenheit temperature back to Celsius by undoing the +32 offset and 9/5 scale.
°C = (°F − 32) × 5/9
Celsius to Kelvin Formula
Kelvin is just Celsius shifted by absolute zero — add 273.15.
K = °C + 273.15
Health
BMI Formula (Body Mass Index)
Population-level weight screen — weight in kilograms divided by height in meters squared.
BMI = weight (kg) ÷ height (m)²
BMR (Mifflin-St Jeor) Formula
Estimate basal metabolic rate — the calories your body burns at rest.
BMR = 10·w + 6.25·h − 5·a + s (s = +5 male, −161 female)
Finance
Math
Fuel Economy Conversion Formula
MPG and L/100km are inversely related — flip and scale to convert.
L/100km = 235.215 ÷ MPG (US)
Area of a Circle Formula
Multiply π by the radius squared.
A = π × r²
Pythagorean Theorem
In any right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides.
a² + b² = c²