What is foot?
A foot is a unit of length in imperial and US customary systems equal to 12 inches. It is commonly used in construction, architecture, body height measurements, and aviation for altitude references.
Real-world uses
Feet are the primary unit for building dimensions, room sizes, and ceiling heights in the United States. Aviation uses feet for altitude worldwide (e.g., cruising at 35,000 ft). Human height in the US and UK is commonly expressed in feet and inches.
History
The foot has been used since ancient civilizations, with varying lengths based on the local king's foot. The modern international foot was defined in 1959 as exactly 0.3048 metres, replacing slightly different US and British survey definitions.
Common mistakes
Using an apostrophe for feet (6') and confusing it with the prime symbol. Also, people often round 1 foot to 30 cm instead of the correct 30.48 cm, leading to cumulative errors in construction.
What is millimetre?
A millimetre is a metric unit of length equal to one thousandth of a metre. It is used in precision manufacturing, medical imaging, engineering tolerances, and detailed technical specifications.
Real-world uses
Millimetres are essential in precision engineering, machining tolerances, and manufacturing specifications. Rainfall is reported in mm by meteorological services worldwide. Dentists measure cavity depths and orthodontic adjustments in millimetres.
History
Part of the original French metric system from the 1790s. The prefix "milli-" derives from the Latin "mille" meaning thousand, indicating one-thousandth of a metre. It became critical with the rise of precision manufacturing in the Industrial Revolution.
Common mistakes
Confusing millimetres with centimetres when reading rulers—each small division on a metric ruler is 1 mm, not 1 cm. Also, mixing up mm with mils (thousandths of an inch) in engineering contexts.
When is this conversion used?
Converting between foot and millimetre is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. This conversion is frequently needed in construction, architecture, and real estate where building codes may specify dimensions in one system while materials are sold in another.
Worked examples
1 foot = 304.8 millimetre
1 millimetre = 0.001 metre
How to convert foot to millimetre
To convert foot to millimetre, multiply the value by 304.8.
To convert millimetre back to foot, multiply by 0.00328084.
Measurement standards
The metre is one of seven SI base units, maintained by the International Bureau of Weights and Measures (BIPM). Since 2019, it is defined by fixing the numerical value of the speed of light in vacuum to exactly 299,792,458 metres per second.
Did you know?
A human hair is roughly 70 micrometres wide, while a single gold atom measures about 0.144 nanometres in diameter — meaning you could line up nearly half a million atoms across the width of one hair.
Quick reference: foot to millimetre
| foot | millimetre |
|---|---|
| 0.1 | 30.48 |
| 0.5 | 152.4 |
| 1 | 304.8 |
| 2 | 609.6 |
| 5 | 1,524 |
| 10 | 3,048 |
| 25 | 7,620 |
| 50 | 15,240 |
| 100 | 30,480 |
| 250 | 76,200 |
| 500 | 152,400 |
| 1,000 | 304,800 |
Common values
| foot | millimetre | |
|---|---|---|
| Height of a door | 6.88976378 foot | 2,100 millimetre |
| Basketball court length | 91.86351706 foot | 28,000 millimetre |
| Football field (soccer) | 344.48818898 foot | 105,000 millimetre |
| Marathon distance | 138,435.03937008 foot | 42,195,000 millimetre |
| Altitude of a cruising airplane | 35,000 foot | 10,668,000 millimetre |