Unit Converters — Length, Weight, Temperature, Volume, Area, Speed, Energy, Data and Cooking

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Why one page per direction

A general-purpose converter with two dropdowns answers every question but explains none of them. When you want to know how many centimetres are in 12 inches, the useful page states the factor once, shows the working, gives a table you can scan without typing, and stops. Each page here does exactly that for a single pair, and the swap link takes you to the reverse pair when you need to go the other way. The live calculator is the same on every page; the prose, the worked examples and the table are specific to the pair.

Exact factors, not rounded ones

Since 1959 the inch has been defined as exactly 2.54 centimetres, the pound as exactly 0.45359237 kilograms and the yard as exactly 0.9144 metres. Everything else in the imperial system follows from those definitions, so the factors on these pages are exact where the definition is exact and stated to ten significant figures where it is not, such as kilograms to pounds. The reference tables are calculated from those factors, not copied from a printed chart, so the row for 100 and the calculator result for 100 always agree.

Temperature is different

Length and weight scale from zero, so converting is a single multiplication. Temperature scales do not share a zero: 0 °C is 32 °F, and 0 °C is 273.15 K. Those conversions multiply and then add, so the temperature pages show the full formula rather than a single factor and the calculator applies both steps. The Kelvin pages are the exception in one direction — Celsius to Kelvin is a straight offset with no scaling — and the pages say so rather than pretending there is a multiplier.

Imperial input the way people write it

Height and length in feet are almost always written as feet and inches, not decimal feet. The feet-to-metres page accepts 5'10", 5 ft 10 in and 5.8333 and treats them as the same value. The inches page accepts feet-and-inches too, so 6'2" converts to 188 cm without working out 74 inches first. Stone is handled the same way in spirit: the stone-to-kilogram page takes whole and fractional stone, and its explainer covers the stone-and-pounds form used on British scales.

Volume, area, speed, energy and data

The same pattern covers litres and gallons, cubic metres and cubic feet, square metres and square feet, hectares and acres, km/h and mph and knots, kilojoules and calories, kilowatt-hours and joules, and gigabytes against megabytes, terabytes and gibibytes. The gallon pages distinguish the US gallon from the imperial one; the speed pages pair the units used in physics, on the road and at sea; the energy pages cover the calorie as it appears on food labels and the kilowatt-hour as it appears on electricity bills. The data pages explain the decimal-versus-binary split and why a 1 TB drive shows up as 931 GB in Windows.

Cooking measures depend on the ingredient

Cups and spoons are volumes, so converting them to grams needs a density for each ingredient and a decision about which cup or spoon the recipe means. The cups to grams, grams to cups and tablespoons to grams pages carry thirty-odd ingredients and make the US, metric, imperial and Australian sizes an explicit choice rather than a guess. The oven temperature converter does Celsius, fan-forced, Fahrenheit and gas mark in any direction.

Cooking ratios

Three pages handle proportion rather than units. The recipe scaler takes a pasted ingredient list and rewrites every quantity for a new number of servings, keeping fractions readable. The baker's percentage calculator turns gram weights into baker's percentages and reports dough hydration, including the effective hydration once the flour and water inside a sourdough starter are counted. The coffee ratio calculator gives grams of coffee for any amount of water, or the reverse, at the standard ratio for pour-over, French press, AeroPress, moka pot, cold brew and espresso.

Print and screen sizes

Pixels only become a physical size once a resolution is attached. The pixels to inches page converts pixels, inches and centimetres at any DPI and shows the answer at 72, 96, 150, 300 and 600. The print size calculator takes an image's pixel dimensions and reports how large it prints at each quality level, with an effective DPI check for the print width you want. The paper sizes reference gives A0 to A7, B-series, Letter, Legal and Tabloid in millimetres, inches and pixels at a chosen DPI.

Everything runs on your device

The factor is in the page, the arithmetic is in the browser, and nothing you type is sent to a server or stored. The pages keep working offline once loaded.