Hong Life CalculatorsUnderstanding the weird units converter — concept and principle
This converter expresses a length, an area or a volume in everyday objects: Olympic swimming pools, football and soccer pitches, tennis and basketball courts, A4 sheets, bank cards, marathons, light-seconds and oil barrels. Use it to make a number easier to picture in a talk, an article or a classroom.
How it is calculated
SI value = your value × unit factor (to m, m² or m³)
Number of objects = SI value ÷ size of one object
- Unit factors: 1 ft = 0.3048 m, 1 mile = 1,609.344 m, 1 ha = 10,000 m², 1 acre = 4,046.856 m², 1 ft² = 0.09290304 m², 1 L = 0.001 m³, 1 US gal = 3.785411784 L.
- Lengths: Olympic pool 50 m, US football field 91.44 m (100 yd between goal lines), soccer pitch 105 m, doubles tennis court 23.77 m, FIBA court 28 m, A4 sheet 297 mm, bank card 85.60 mm, marathon 42.195 km, light-second 299,792,458 m.
- Areas use the full rectangle of each object; volumes use a 2 m deep pool (2,500 m³) and a 42-gallon oil barrel (158.987 L).
- Rows that make no sense for the kind of quantity, such as a barrel of length, show —.
The principle
Every conversion is a division by a reference size. Converting to SI units first means all objects can be compared on the same footing. The objects were chosen because their sizes are fixed by standards or rules: the pool by World Aquatics, the pitch by FIFA's recommendation, the courts by the ITF and FIBA, the paper by ISO 216 and the card by ISO/IEC 7810. Lengths are compared with the long side of each object; areas with its full surface.
Worked example
Default inputs: 1 kilometre.
- SI value = 1 × 1,000 = 1,000 m.
- Olympic pools = 1,000 ÷ 50 = 20; US football fields = 1,000 ÷ 91.44 = 10.94.
- Soccer pitches = 1,000 ÷ 105 = 9.524; tennis courts = 1,000 ÷ 23.77 = 42.07; basketball courts = 1,000 ÷ 28 = 35.71.
- A4 sheets end to end = 1,000 ÷ 0.297 = 3,367; bank cards = 1,000 ÷ 0.0856 = 11,682, shown as 11,680.
- Marathons = 1,000 ÷ 42,195 = 0.0237; light-seconds = 1,000 ÷ 299,792,458 = 0.000003336.
| Value | Olympic swimming pools |
|---|---|
| 0.25 | 5 |
| 0.5 | 10 |
| 0.75 | 15 |
| 1 | 20 |
| 1.25 | 25 |
| 1.5 | 30 |
| 2 | 40 |
How to read the result
Pick the comparison your audience knows best. Football fields and pools work well for areas and long distances; A4 sheets and bank cards work for small lengths. The results are shown to four significant figures, which is more precise than any everyday comparison needs. Remember which dimension was used: "10.94 football fields" means end to end along their length.
Common mistakes
- Mixing a length comparison with an area comparison.
- Assuming every pool is Olympic size; many public pools are 25 m.
- Including the end zones of an American football field (that is 120 yd, not 100).
- Expecting a volume for a length unit.
Frequently asked questions
How many football fields is a mile?
About 17.6 fields of 100 yards between the goal lines.
How much water is in an Olympic pool?
About 2,500 m³ (2.5 million litres) at 2 m depth.
How long is a light-second?
299,792,458 m, the distance light travels in one second.
Sources: NIST Special Publication 811 (unit definitions) · ISO 216 (A-series paper sizes) and ISO/IEC 7810 (ID-1 card size)