Unit Converter

The metric system (formally the International System of Units, or SI) was developed in France in the 1790s and adopted by nearly every country over the following two centuries. It uses base-10 prefixes — kilo (1,000), centi (1/100), milli (1/1,000) — making conversions within the system simple multiplication or division by powers of ten. One kilometer is exactly 1,000 meters. One kilogram is exactly 1,000 grams.

The imperial system evolved from English units used for centuries before standardization. Its conversion factors are irregular: 12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile, 16 ounces in a pound, 8 pints in a gallon. The United States customary system is nearly identical to imperial but differs slightly in volume measurements — a US gallon is about 3.785 liters versus 4.546 liters for an imperial gallon.

In practice, even countries that officially use the metric system retain some traditional units. The UK measures body weight in stone and road distances in miles. Canada uses Fahrenheit informally for cooking alongside Celsius for weather. Knowing both systems is practical regardless of where you live.

Length: 1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 mile = 1.609 km. 1 meter = 3.281 feet. For a quick mental estimate, multiply miles by 1.6 to get kilometers, or multiply kilometers by 0.6 to get miles.

Weight: 1 pound = 453.6 grams. 1 kilogram = 2.205 pounds. 1 ounce = 28.35 grams. For rough estimates, divide pounds by 2.2 to get kilograms, or multiply kilograms by 2.2 to get pounds.

Volume: 1 gallon (US) = 3.785 liters. 1 liter = 33.81 fluid ounces. 1 cup = 236.6 mL. For quick cooking conversions, 1 liter is roughly 4.2 cups, and 1 tablespoon is about 15 mL.

Temperature: To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9. To convert Celsius to Fahrenheit, multiply by 9/5 and add 32. Key reference points: water freezes at 0C / 32F, boils at 100C / 212F, and normal body temperature is 37C / 98.6F.

Temperature is the trickiest conversion because the scales do not share a common zero point. Fahrenheit and Celsius intersect at -40 degrees — the only temperature that reads the same on both scales. The formula C = (F - 32) x 5/9 works for any value, but a few mental shortcuts help for everyday use.

For a rough estimate, subtract 30 from the Fahrenheit value and divide by 2. This gives you a number within a few degrees of the actual Celsius value for typical weather temperatures. For example, 80F: (80 - 30) / 2 = 25C (the exact answer is 26.7C). It breaks down at extreme temperatures but works well in the 30-100F range.

The Kelvin scale, used in science, starts at absolute zero (-273.15C). To convert Celsius to Kelvin, simply add 273.15. Room temperature (about 22C) is 295.15K. Kelvin uses the same degree size as Celsius, so temperature differences are identical in both scales.

Recipes from different countries use different measurement systems, which can cause confusion in the kitchen. American recipes rely on volume measurements — cups, tablespoons, teaspoons — while European and professional recipes typically use weight in grams. Weight is more precise because the volume of ingredients like flour varies depending on how tightly it is packed.

Key kitchen equivalents: 1 cup = 16 tablespoons = 48 teaspoons = 236.6 mL. 1 tablespoon = 3 teaspoons = 14.8 mL. 1 stick of butter = 1/2 cup = 113 grams. 1 cup of all-purpose flour weighs about 120-130 grams depending on scooping method. 1 cup of granulated sugar weighs about 200 grams.

When converting between volume and weight for cooking, note that the relationship depends on the ingredient's density. A cup of water weighs 236 grams, but a cup of honey weighs about 340 grams, and a cup of sifted powdered sugar weighs only about 115 grams. For baking accuracy, always use a kitchen scale when a recipe provides gram measurements.

Data units follow a base-2 system in computing but are often marketed using base-10 numbers, which creates confusion. In the binary system used by operating systems, 1 kilobyte (KB) = 1,024 bytes, 1 megabyte (MB) = 1,024 KB, 1 gigabyte (GB) = 1,024 MB, and 1 terabyte (TB) = 1,024 GB. Storage manufacturers use base-10 definitions where 1 GB = 1,000 MB, which is why a "500 GB" hard drive shows about 465 GB in your operating system.

Internet speeds are measured in megabits per second (Mbps), not megabytes. There are 8 bits in a byte, so a 100 Mbps connection can transfer about 12.5 megabytes per second under ideal conditions. When estimating download times, divide your connection speed by 8 to get the approximate transfer rate in megabytes per second.