Unit Conversion Guide: Temperature, Length, Weight, Volume & More
The essential unit conversion reference: exact formulas for Fahrenheit↔Celsius, miles↔kilometers, pounds↔kilograms, gallons↔liters, and more — with worked examples.
Temperature Conversion: Fahrenheit, Celsius & Kelvin
Temperature conversion between Fahrenheit (used in US everyday life) and Celsius (international scientific standard) requires both multiplication and addition — it is a linear but non-proportional relationship because the zero points differ. Kelvin (K) is the SI base unit for temperature, used in science and engineering. 0K = absolute zero = −273.1
Length Conversion: Miles, Kilometers, Feet, Meters & Inches
The metric system uses base-10 scaling (milli-, centi-, kilo-), making metric-to-metric conversions trivially simple. US customary length units have irregular relationships (12 inches = 1 foot, 3 feet = 1 yard, 5,280 feet = 1 mile) that require exact multipliers. The most common conversion need for American travelers: miles to kilometers. The exact
Weight & Mass: Pounds, Kilograms & Ounces
In everyday use, weight and mass are used interchangeably, though physicists distinguish them (weight = mass × gravity). The most important everyday conversion is pounds (lb) to kilograms (kg) — critical for medication dosing, international shipping, and fitness tracking. The exact conversion: 1 lb = 0.453592 kg. A quick mental math trick: multiply
Volume: Gallons, Liters, Cups & Milliliters
Volume conversions are essential for cooking, fuel purchasing, and scientific measurement. The US customary and imperial systems diverge here: a US gallon (3.785 L) is smaller than an imperial UK gallon (4.546 L) — a common source of confusion for recipe conversions involving UK cookbooks. For US cooking: 1 cup = 240 mL (rounded; exact = 236.6 mL).
Frequently Asked Questions
What is the easiest way to convert Celsius to Fahrenheit in your head?
Double the Celsius temperature and add 30 for a quick estimate. 20°C → (20×2)+30 = 70°F (actual: 68°F). 35°C → (35×2)+30 = 100°F (actual: 95°F). The estimate is off by 3–5°F but good enough for everyday weather conversations.
Why does the US use imperial instead of metric?
The US officially adopted the metric system as the preferred system for trade and commerce in the Metric Conversion Act of 1975, but usage remained voluntary. Most industries (science, medicine, military, manufacturing) already use metric. Everyday consumer use of miles, pounds,
How many cups are in a liter?
1 liter = 4.227 US cups (using the exact 236.588 mL per cup). For practical cooking purposes, treat 1 liter as just over 4 cups or 4 cups + 3 tablespoons.
What is the difference between a US gallon and a UK gallon?
A US gallon = 3.785 liters. A UK (imperial) gallon = 4.546 liters — about 20% larger. This difference significantly affects fuel economy comparisons: a car that gets 40 mpg in the UK gets only about 33 mpg by US measurement for identical fuel consumption.
How do I convert inches to centimeters?
1 inch = 2.54 centimeters (this is exact by international definition). To convert inches to cm: multiply by 2.54. To convert cm to inches: divide by 2.54. Quick mental math: 10 cm ≈ 4 inches; 30 cm ≈ 12 inches (1 foot); 100 cm = 39.37 inches (slightly more than 3 feet).