Unit Converters
Choose a specific conversion for a page that shows the formula, a worked example and common values, or open the Unit Converter to pick any pair of units yourself.
Open the Unit Converter to choose any two units yourself.
Length conversions
Inches, feet and miles are defined exactly in terms of the meter, so these conversions use exact constants. The pages below cover the pairs people search for most, in both directions.
| Conversion | Formula | Typical use |
|---|---|---|
| CM to Inches Converter | inches = centimeters / 2.54 | Furniture, clothing and product sizes |
| Inches to CM Converter | centimeters = inches ร 2.54 | Frames, prints and sizes quoted in inches |
| MM to Inches Converter | inches = millimeters / 25.4 | Hardware, parts and technical drawings |
| KM to Miles Converter | miles = kilometers / 1.609344 | Road distance, running and maps |
| Miles to KM Converter | kilometers = miles ร 1.609344 | Road trips and mile-based running distances |
| Meters to Feet Converter | feet = meters / 0.3048 | Rooms, heights and building measurements |
| Feet to Meters Converter | meters = feet ร 0.3048 | Heights, lumber and elevations |
Weight and mass conversions
These two use the international avoirdupois pound, which is exactly 0.45359237 kilograms. For ounces, stone, grams, milligrams and metric tonnes, use the Unit Converter.
| Conversion | Formula | Typical use |
|---|---|---|
| KG to LBS Converter | pounds = kilograms / 0.45359237 | Body weight, luggage and shipping |
| LBS to KG Converter | kilograms = pounds ร 0.45359237 | Scales, packages and gym plates in pounds |
Temperature conversions
Celsius and Fahrenheit differ in both the size of a degree and where zero sits, so converting needs an offset as well as a multiplication.
| Conversion | Formula | Typical use |
|---|---|---|
| Celsius to Fahrenheit Converter | ยฐF = (ยฐC ร 9/5) + 32 | Weather, cooking and room temperature |
| Fahrenheit to Celsius Converter | ยฐC = (ยฐF - 32) ร 5/9 | US forecasts, thermostats and recipes |
Speed and area conversions
Speed (meters per second, kilometers per hour, miles per hour and knots) and area (square millimeters up to square miles, plus acres and hectares) do not have their own pages yet. The Unit Converter converts both, and lets you pick any two units in the category.
How these converters work
Every page here uses the same conversion engine as the Unit Converter, so the tables, formulas and the calculator on each page always agree. Conversions are calculated in your browser.
Results are shown to up to 12 significant digits with trailing zeros removed. Where a unit is defined exactly, the constant is exact. A displayed result can still be rounded, because dividing by an exact constant does not always end.
| Definition | Category |
|---|---|
| 1 inch = 0.0254 meters | Length |
| 1 foot = 0.3048 meters | Length |
| 1 yard = 0.9144 meters | Length |
| 1 mile = 1609.344 meters | Length |
| 1 pound = 0.45359237 kilograms | Mass / Weight |
| 1 ounce = 0.028349523125 kilograms | Mass / Weight |
| 1 stone = 6.35029318 kilograms | Mass / Weight |
| 1 acre = 43560 square feet | Area |
| 1 hectare = 10000 square meters | Area |
| 1 mile per hour = 0.44704 meters per second | Speed |
| 1 knot = 1852 meters per hour, or one nautical mile per hour | Speed |
Common questions
Are the conversions exact?
The unit definitions are exact where an international definition exists, such as 1 inch = 2.54 cm and 1 pound = 0.45359237 kg. The results are shown to up to 12 significant digits, so a long decimal is rounded for display even when the definition behind it is exact.
Which units can the Unit Converter handle?
Length: mm, cm, m, km, in, ft, yd, mi. Mass / Weight: mg, g, kg, oz, lb, st, t. Temperature: ยฐC, ยฐF. Speed: m/s, km/h, mph, kn. Area: mmยฒ, cmยฒ, mยฒ, kmยฒ, inยฒ, ftยฒ, ydยฒ, ac, ha, miยฒ.
Why are there separate pages for each conversion?
Each page opens the same converter with a conversion already chosen, and adds the formula, a worked example, a table of common values and answers specific to that pair. They are shortcuts into one tool, not separate calculators.
Do my numbers leave my device?
No. The conversions are calculated in your browser, and nothing you enter is sent to a server.
Related pages
- Unit Converter: every category and unit in one converter.
- Utilities: the other small tools that sit alongside the converters.
- Online Ruler: measure something on your screen in millimeters, centimeters or inches.