There are exactly 2.54 centimetres in one inch. The inch was redefined in 1959 by international agreement as exactly 25.4 mm. To convert inches to centimetres, multiply by 2.54. For example, 5 inches = 12.7 cm. Conversely, divide centimetres by 2.54 to get inches.

To convert Fahrenheit to Celsius, subtract 32, then multiply by 5/9. Formula: °C = (°F − 32) × 5/9. For example, 98.6°F = (98.6 − 32) × 5/9 = 37°C. To go the other way: °F = (°C × 9/5) + 32.

One US cup equals 236.59 ml. A metric cup (used in Australia, Canada and New Zealand) equals exactly 250 ml. When following international recipes, it is worth checking which cup measure is intended, as the difference adds up in baking.

One metre equals 3.28084 feet. To convert metres to feet, multiply by 3.28084. To convert feet to metres, multiply by 0.3048. For a quick rough estimate, 1 metre ≈ 3 feet 3 inches.

One pound equals exactly 0.45359237 kilograms. One kilogram equals 2.20462 pounds. To convert pounds to kg, multiply by 0.4536. A useful shortcut: divide pounds by 2.2 for a quick kg estimate.

1 mile per hour equals 1.60934 km/h. To convert mph to km/h, multiply by 1.60934. A useful rule of thumb: 60 mph ≈ 96.6 km/h, and 100 km/h ≈ 62.1 mph.

In binary (as used by operating systems), 1 TB = 1,024 GB. Hard drive manufacturers often use decimal, where 1 TB = 1,000 GB. This is why a 1 TB drive shows as approximately 931 GB in your OS.

There are 16 tablespoons in one US cup. One tablespoon equals 3 teaspoons and approximately 14.79 ml. Half a cup = 8 tablespoons; a quarter cup = 4 tablespoons.

One hectare equals 2.47105 acres. A hectare is 10,000 m² (a square 100m × 100m). An acre is approximately 4,047 m² or 43,560 square feet. Hectares are used in most countries; acres are common in the US and UK.

One US gallon equals 3.78541 litres. One imperial (UK) gallon equals 4.54609 litres. US gallons are approximately 20% smaller than UK gallons, which matters when comparing fuel economy figures across countries.

Absolute zero is −273.15°C or −459.67°F. It is the theoretical lowest possible temperature, at which atoms have minimum thermal motion. On the Kelvin scale, absolute zero is 0 K — the starting point of the scale.

One pound (lb) equals 16 ounces (oz) in the avoirdupois system used for everyday weight measurement. To convert pounds to ounces, multiply by 16. One ounce equals 28.3495 grams, so one pound equals approximately 453.59 grams.

A knot is one nautical mile per hour. One knot equals exactly 1.852 km/h or approximately 1.151 mph. Knots are the international standard unit of speed for maritime navigation and aviation.

One ounce equals 28.3495 grams. To convert ounces to grams, multiply by 28.3495. There are 16 ounces in one pound, which equals approximately 453.59 grams.

A stone is a unit of weight equal to 14 pounds or approximately 6.35 kilograms. The stone (st) is used primarily in the United Kingdom and Ireland for measuring body weight. It is not used in most other countries.

One kilometre equals 0.621371 miles. One mile equals 1.60934 kilometres. A useful rough conversion: 8 km ≈ 5 miles, or 5 miles ≈ 8 km.

A US gallon equals 3.78541 litres. A UK imperial gallon equals 4.54609 litres, making it approximately 20% larger. This matters when comparing fuel economy: a car described as achieving 40 mpg on US gallons performs differently to one achieving 40 mpg on UK gallons.

To convert Celsius to Kelvin, add 273.15. Formula: K = °C + 273.15. For example, 0°C = 273.15 K and 100°C = 373.15 K. The Kelvin and Celsius scales have identical degree intervals — Kelvin starts at absolute zero rather than the freezing point of water.

A bit is the smallest unit of digital information, with a value of either 0 or 1. A byte equals 8 bits and can represent 256 different values. Storage capacity (files, drives, memory) is measured in bytes — KB, MB, GB, TB. Internet and network speeds are measured in bits per second (Mbps, Gbps), so a 100 Mbps connection transfers approximately 12.5 megabytes per second.

One acre equals 43,560 square feet. This is equivalent to a square plot approximately 208.7 feet (63.6 m) on each side. One acre also equals approximately 4,047 square metres or 0.4047 hectares.

To convert square metres to square feet, multiply by 10.7639. To convert square feet to square metres, multiply by 0.0929. For example, 100 m² = 1,076.39 sq ft, and 1,000 sq ft ≈ 92.9 m².

One tablespoon equals exactly 3 teaspoons. One US tablespoon is approximately 14.79 ml and one US teaspoon is approximately 4.93 ml. There are 48 teaspoons and 16 tablespoons in one US cup.