| fermi | 1 fm | 2 fm | 3 fm | 4 fm | 5 fm | 6 fm | 7 fm | 8 fm | 9 fm | 10 fm | 11 fm | 12 fm | 13 fm | 14 fm | 15 fm | 16 fm | 17 fm | 18 fm | 19 fm | 20 fm | 21 fm | 22 fm | 23 fm | 24 fm | 25 fm | 26 fm | 27 fm | 28 fm | 29 fm | 30 fm | 31 fm | 32 fm | 33 fm | 34 fm | 35 fm | 36 fm | 37 fm | 38 fm | 39 fm | 40 fm | 41 fm | 42 fm | 43 fm | 44 fm | 45 fm | 46 fm | 47 fm | 48 fm | 49 fm | 50 fm | 51 fm | 52 fm | 53 fm | 54 fm | 55 fm | 56 fm | 57 fm | 58 fm | 59 fm | 60 fm | 61 fm | 62 fm | 63 fm | 64 fm | 65 fm | 66 fm | 67 fm | 68 fm | 69 fm | 70 fm | 71 fm | 72 fm | 73 fm | 74 fm | 75 fm | 76 fm | 77 fm | 78 fm | 79 fm | 80 fm | 81 fm | 82 fm | 83 fm | 84 fm | 85 fm | 86 fm | 87 fm | 88 fm | 89 fm | 90 fm | 91 fm | 92 fm | 93 fm | 94 fm | 95 fm | 96 fm | 97 fm | 98 fm | 99 fm | 100 fm |
| metric inch | 2.5 × 10-12 in (metric) | 5.0 × 10-12 in (metric) | 7.5 × 10-12 in (metric) | 1.0 × 10-11 in (metric) | 1.25 × 10-11 in (metric) | 1.5 × 10-11 in (metric) | 1.75 × 10-11 in (metric) | 2.0 × 10-11 in (metric) | 2.25 × 10-11 in (metric) | 2.5 × 10-11 in (metric) | 2.75 × 10-11 in (metric) | 3.0 × 10-11 in (metric) | 3.25 × 10-11 in (metric) | 3.5 × 10-11 in (metric) | 3.75 × 10-11 in (metric) | 4.0 × 10-11 in (metric) | 4.25 × 10-11 in (metric) | 4.5 × 10-11 in (metric) | 4.75 × 10-11 in (metric) | 5.0 × 10-11 in (metric) | 5.25 × 10-11 in (metric) | 5.5 × 10-11 in (metric) | 5.75 × 10-11 in (metric) | 6.0 × 10-11 in (metric) | 6.25 × 10-11 in (metric) | 6.5 × 10-11 in (metric) | 6.75 × 10-11 in (metric) | 7.0 × 10-11 in (metric) | 7.25 × 10-11 in (metric) | 7.5 × 10-11 in (metric) | 7.75 × 10-11 in (metric) | 8.0 × 10-11 in (metric) | 8.25 × 10-11 in (metric) | 8.5 × 10-11 in (metric) | 8.75 × 10-11 in (metric) | 9.0 × 10-11 in (metric) | 9.25 × 10-11 in (metric) | 9.5 × 10-11 in (metric) | 9.75 × 10-11 in (metric) | 1.0 × 10-10 in (metric) | 1.025 × 10-10 in (metric) | 1.05 × 10-10 in (metric) | 1.075 × 10-10 in (metric) | 1.1 × 10-10 in (metric) | 1.125 × 10-10 in (metric) | 1.15 × 10-10 in (metric) | 1.175 × 10-10 in (metric) | 1.2 × 10-10 in (metric) | 1.225 × 10-10 in (metric) | 1.25 × 10-10 in (metric) | 1.275 × 10-10 in (metric) | 1.3 × 10-10 in (metric) | 1.325 × 10-10 in (metric) | 1.35 × 10-10 in (metric) | 1.375 × 10-10 in (metric) | 1.4 × 10-10 in (metric) | 1.425 × 10-10 in (metric) | 1.45 × 10-10 in (metric) | 1.475 × 10-10 in (metric) | 1.5 × 10-10 in (metric) | 1.525 × 10-10 in (metric) | 1.55 × 10-10 in (metric) | 1.575 × 10-10 in (metric) | 1.6 × 10-10 in (metric) | 1.625 × 10-10 in (metric) | 1.65 × 10-10 in (metric) | 1.675 × 10-10 in (metric) | 1.7 × 10-10 in (metric) | 1.725 × 10-10 in (metric) | 1.75 × 10-10 in (metric) | 1.775 × 10-10 in (metric) | 1.8 × 10-10 in (metric) | 1.825 × 10-10 in (metric) | 1.85 × 10-10 in (metric) | 1.875 × 10-10 in (metric) | 1.9 × 10-10 in (metric) | 1.925 × 10-10 in (metric) | 1.95 × 10-10 in (metric) | 1.975 × 10-10 in (metric) | 2.0 × 10-10 in (metric) | 2.025 × 10-10 in (metric) | 2.05 × 10-10 in (metric) | 2.075 × 10-10 in (metric) | 2.1 × 10-10 in (metric) | 2.125 × 10-10 in (metric) | 2.15 × 10-10 in (metric) | 2.175 × 10-10 in (metric) | 2.2 × 10-10 in (metric) | 2.225 × 10-10 in (metric) | 2.25 × 10-10 in (metric) | 2.275 × 10-10 in (metric) | 2.3 × 10-10 in (metric) | 2.325 × 10-10 in (metric) | 2.35 × 10-10 in (metric) | 2.375 × 10-10 in (metric) | 2.4 × 10-10 in (metric) | 2.425 × 10-10 in (metric) | 2.45 × 10-10 in (metric) | 2.475 × 10-10 in (metric) | 2.5 × 10-10 in (metric) |
The femtometre (American spelling femtometer, symbol fm derived from the Danish and Norwegian word femten, "fifteen"+Ancient Greek: μέτρον, metrοn, "unit of measurement") is an SI unit of length equal to 10−15 metres, which means a quadrillionth of one. This distance can also be called a fermi and was so named in honour of physicist Enrico Fermi, as it is a typical length-scale of nuclear physics.
| Name of unit | Symbol | Definition | Relation to SI units | Unit System |
|---|---|---|---|---|
| fermi | fm | ≡ 1×10−15 m | ≡ 1×10−15 m | Metric system Non-SI |
| fermi | metric inches | fermi | metric inches |
|---|---|---|---|
| 1 | = 2.5E-12 | 4 | = 1.0E-11 |
| 1.5 | = 3.75E-12 | 4.5 | = 1.125E-11 |
| 2 | = 5.0E-12 | 5 | = 1.25E-11 |
| 2.5 | = 6.25E-12 | 5.5 | = 1.375E-11 |
| 3 | = 7.5E-12 | 6 | = 1.5E-11 |
A metric inch is a nickname for a preferred 1⁄4 subdivision of an ISO 2848 basic module, or 1⁄12 of a metric foot measuring 25 millimetres (0.984 in). A metric inch is 0.4 millimetres (0.016 in) shorter than an inch.
The term was similarly used to refer to the historical Soviet Bloc practice of spacing integrated circuit pins at 1⁄10 of a 25 mm "metric inch" length, instead of the western practice of 1⁄10 of an imperial inch.
| Name of unit | Symbol | Definition | Relation to SI units | Unit System |
|---|---|---|---|---|
| metric inch | in (metric) | = 0.016 in | = 0.0004 m | Metric system SI |
| metric inches | fermi | metric inches | fermi |
|---|---|---|---|
| 1 | = 400000000000 | 4 | = 1600000000000 |
| 1.5 | = 600000000000 | 4.5 | = 1800000000000 |
| 2 | = 800000000000 | 5 | = 2000000000000 |
| 2.5 | = 1000000000000 | 5.5 | = 2200000000000 |
| 3 | = 1200000000000 | 6 | = 2400000000000 |
| fermi | metric inches |
|---|---|
| 1 | = 2.5 × 10-12 |
| 400 000 000 000 | = 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |