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Convert units
Length, mass, temperature and more — instant results, no account.
Comma or dot is a decimal mark (1,234 = 1.234). No thousands separators. Up to 18 digits; exponent −24 to 24; |value| ≤ 10²⁴.
Up to 12 significant digits. ≈ means rounded.
Favourites
History
History and favourites stay on this device. Save up to 100 results and 50 unit pairs.
Optional Android app
Convert without an internet connection
Keep the converter handy on your phone. The Android app works without an account and lets you return to saved results, even offline.
- 7 categories and 38 units with results as you type
- Favourite pairs, local history and remembered settings
- Copy or share results with their units
Core functions are free. The app includes a small Google AdMob banner; ads need internet. Calculations and saved entries stay local. The online converter above works independently of installing the app. App privacy policy
Convert units without mixing quantities
The converter compares a quantity expressed in different units. Start with the category: metres describe length, square metres describe area and cubic metres describe volume. These quantities are not interchangeable. Litres cannot be converted to kilograms without knowing density.
How to use the converter
Choose a category and source unit, enter a value, then choose the target unit. The result updates immediately. Swapping exchanges the units while keeping your input value. Copy includes both units. Favourites remember unit pairs; history saves a result only when you press “Save to history”.
Decimal marks and grouping
2,54 and 2.54 mean the same number. Thousands separators are not supported: 1,234 always means one point two three four, including in English. Enter 1234 for one thousand two hundred and thirty-four. Scientific notation 1e3 means 1000. Spaces within numbers and mixed decimal marks are rejected.
Length: centimetres and inches
The international inch is exactly 0.0254 m. A foot contains 12 inches, a yard 3 feet and a land mile 5280 feet. Nautical miles and historical survey feet are not included.
Area and volume: raise the factor to a power
A metre contains 100 cm. A square with a one-metre side therefore covers 100 × 100 = 10 000 cm². A cube with one-metre edges contains 100 × 100 × 100 = 1 000 000 cm³. Multiplying by the length factor alone gives the wrong area or volume. A hectare is exactly 10 000 m².
Litres and two kinds of gallon
A litre is exactly 1 dm³ or 1000 cm³. The US liquid gallon is exactly 3.785411784 l, defined as 231 cubic inches. The imperial gallon is 4.54609 l. Choose the version stated on the product. The US dry gallon is not supported and must not be confused with the liquid gallon.
Mass: pounds and ounces
The converter uses the avoirdupois pound, exactly 0.45359237 kg. An avoirdupois ounce is 1/16 of that pound, or 28.349523125 g. Troy ounces and fluid ounces are different units. The symbol t means the metric tonne of 1000 kg.
Temperature needs an offset
For absolute temperatures, °F = °C × 9/5 + 32 and K = °C + 273.15. Thus 0°C equals 32°F and 273.15 K. Do not use this form for temperature differences: a rise of 10°C is a rise of 18°F, rather than a temperature of 50°F. Values below 0 K are rejected.
Speed and duration
1 m/s is exactly 3.6 km/h. mph means land miles per hour. Here a day lasts 24 hours and a week is seven such days. These are durations, not calendar calculations. Daylight saving time, time zones and leap seconds are not included. Months and years do not have a constant duration.
Rounding and limits
Factors based on definitions are exact, but division may produce a non-terminating decimal. The converter calculates with fractions and rounds only the display to 12 significant digits. ≈ marks a rounded display. This does not imply twelve-digit measurement accuracy. For technical work, allow for measurement tolerances and the applicable standard. This tool does not replace a measuring instrument.
Saved entries, removal and privacy
Favourites, history and settings are stored locally. Removal asks for confirmation. Undo restores the most recently removed entries during the current session; closing the app ends that opportunity. Clearing app or browser data also removes saved entries. There is no synchronisation or cloud backup.
Frequently asked questions
Can I convert kilograms to litres? Only if the substance’s density is known. Why allow negative lengths? Signed values can describe displacement, rather than a negative physical size. Is the result exact? A definition may be exact, while its display and your measurements have separate limits. Do favourites need an account? No, they stay on your device.
Worked examples
1 in = 2.54 cm · 1 ft = 0.3048 m
1 m² = 10 000 cm² · 1 l = 1000 cm³
0°C = 32°F = 273.15 K
36 km/h = 10 m/s · 90 min = 1.5 h
Sources and definitions
BIPM — SI Brochure, 9 (2026) · NIST — SP 811, Appendix B.9
2026-10-30 · ARWIVO