Free tools
Free Unit Converters
Updated 27 September 2026 · 4 min read
Recipes in cups, heights in feet, speed limits in mph, storage in gibibytes — the world never agreed on one set of units. KitWren has 123 free converters that give an instant answer as you type, show the formula, and include a conversion table. For the most-searched values, there are ready-made answer pages too, like 170 cm in feet.
Open the free Centimetres to FeetWhat you can convert
| Category | Units include | Popular converters |
|---|---|---|
| Length | mm, cm, m, km, inches, feet, yards, miles, nautical miles | cm to feet, inches to cm, miles to km |
| Weight | g, kg, tonnes, ounces, pounds, stone, carats, troy ounces | kg to lbs, stone to kg |
| Temperature | Celsius, Fahrenheit, Kelvin, Rankine | Fahrenheit to Celsius, Celsius to Fahrenheit |
| Cooking | US and metric cups, tablespoons, teaspoons, grams by ingredient | cups to ml, ml to cups |
| Speed | km/h, mph, m/s, knots, Mach | mph to km/h |
| Area, volume | m², ft², acres, hectares, litres, gallons (US and UK), cubic metres | — |
| Science and tech | pressure, energy, power, data (KB vs KiB), frequency, angle, time, fuel economy | — |
Ready-made answer pages
Many people search for one exact value rather than a converter. For the most common units, KitWren has a page for each popular value, showing the answer, the calculation, a friendly form (such as feet and inches) and nearby values:
There are over a thousand of these pages, covering heights, body weights, running distances, oven temperatures, speed limits and more.
Five mental shortcuts
No calculator? These get you close enough for everyday decisions:
| Conversion | Shortcut | Example | Exact |
|---|---|---|---|
| kg → lb | Double it, then add 10% | 70 kg → 140 + 14 = 154 lb | 154.3 lb |
| miles → km | Multiply by 1.6 | 5 mi → 8 km | 8.05 km |
| °F → °C | Subtract 30, then halve | 70 °F → 20 °C | 21.1 °C |
| cm → inches | Multiply by 4, divide by 10 | 30 cm → 12 in | 11.8 in |
| litres → US gallons | Divide by 4 | 40 L → 10 gal | 10.6 gal |
Cooking: the cup problem
A US cup is 236.6 ml, while the metric cup used in Australia, New Zealand and elsewhere is 250 ml — a 6% difference that matters in baking. And a cup of flour weighs far less than a cup of sugar, so volume-to-weight conversions depend on the ingredient. The cooking converter lets you choose the cup type and the ingredient (flour, sugar, butter, rice, oats, honey and more) for a realistic weight. Ingredient weights are averages; for exact baking, weigh.
Traps worth knowing
- US vs UK gallons and pints. A UK gallon is about 20% larger than a US gallon, which also changes miles per gallon.
- KB vs KiB. Storage makers use 1 KB = 1,000 bytes; many operating systems count 1,024. That’s why a “1 TB” drive shows as about 931 GB.
- Fuel economy runs backwards. Higher mpg is better, but lower L/100 km is better.
- Stone. One stone is 14 pounds — common for body weight in the UK and Ireland.
Everyday situations
- Travel: a 100 km/h speed limit is about 62 mph; a 30 °C forecast is 86 °F; a 10 km walk is a little over 6 miles.
- Health and fitness: a height of 180 cm is 5 ft 11 in; 11 stone is about 70 kg; a marathon is 42.2 km, or 26.2 miles.
- Home and DIY: a room of 20 m² is about 215 ft²; a 2.4 m ceiling is roughly 7 ft 10 in.
- Kitchen: 350 °F — a common oven temperature in US recipes — is about 175–180 °C; a US stick of butter is about 113 g.
- Tech: a 100 Mbit/s internet plan downloads at most about 12.5 MB per second, because there are 8 bits in a byte.
Each converter also shows a table of common values, which is handy for printing and sticking on the fridge or workshop wall.
Fast and private
Converters run in your browser, update as you type, and work on any device. They’re free, need no account, and show the formula so you can check the maths — handy for homework. For conversions related to dates and time zones, see the time zone converter.