The fetal crown rump length (CRL) is defined as the longest length excluding the limbs & yolk sac. It is the measurements between the top of the head to the area above where the legs begin and done by ultrasound usually up to the 14th week of the pregnancy .

The original definition of a crown rump length (CRL) was by Mall in 1907. The CRL is the sitting height, mid brain to the lowest point of breech.
| Days (LMP) | Days (Fertilization) | (weeks/days) | (mm) |
| 37 | 23 | 5.2 | 1 |
| 38 | 24 | 5.3 | 2 |
| 39 | 25 | 5.4 | 3 |
| 40 | 26 | 5.5 | 3 |
| 41 | 27 | 5.6 | 4 |
| 42 | 28 | 6 | 4 |
| 43 | 29 | 6.1 | 5 |
| 44 | 30 | 6.2 | 6 |
| 45 | 31 | 6.3 | 7 |
| 46 | 32 | 6.4 | 8 |
| 47 | 33 | 6.5 | 9 |
| 48 | 34 | 6.6 | 10 |
| 49 | 35 | 7 | 11 |
| 50 | 36 | 7.1 | 11 |
| 51 | 37 | 7.2 | 12 |
| 52 | 38 | 7.3 | 12 |
| 53 | 39 | 7.4 | 13 |
| 54 | 40 | 7.5 | 14 |
| 55 | 41 | 7.6 | 15 |
| 56 | 42 | 8 | 17 |
| 57 | 43 | 8.1 | 18 |
| 58 | 44 | 8.2 | 19 |
| 59 | 45 | 8.3 | 20 |
| 60 | 46 | 8.4 | 21 |
| 61 | 47 | 8.5 | 22 |
| 62 | 48 | 8.6 | 22 |
| 63 | 49 | 9 | 23 |
| 64 | 50 | 9.1 | 24 |
| 65 | 51 | 9.2 | 26 |
| 66 | 52 | 9.3 | 27 |
| 67 | 53 | 9.4 | 28 |
| 68 | 54 | 9.5 | 29 |
| 69 | 55 | 9.6 | 31 |
| 70 | 56 | 10 | 34 |
| 71 | 57 | 10.1 | 36 |
| 72 | 58 | 10.2 | 37 |
| 73 | 59 | 10.3 | 38 |
| 74 | 60 | 10.4 | 39 |
| 75 | 61 | 10.5 | 39 |
| 76 | 62 | 10.6 | 40 |
| 77 | 63 | 11 | 44 |
| 78 | 64 | 11.1 | 45 |
| 79 | 65 | 11.2 | 47 |
| 80 | 66 | 11.3 | 48 |
| 81 | 67 | 11.4 | 52 |
| 82 | 68 | 11.5 | 55 |
| 83 | 69 | 11.6 | 56 |
| 84 | 70 | 12 | 57 |
| 85 | 71 | 12.1 | 58 |
| 86 | 72 | 12.2 | 60 |
| 87 | 73 | 12.3 | 61 |
| 88 | 74 | 12.4 | 63 |
| 89 | 75 | 12.5 | 64 |
| 90 | 76 | 12.6 | 65 |
| 91 | 77 | 13 | 68 |
| 92 | 78 | 13.1 | 70 |
| 93 | 79 | 13.2 | 72 |
| 94 | 80 | 13.3 | 74 |
| 95 | 81 | 13.4 | 76 |
| 96 | 82 | 13.5 | 77 |
| 97 | 83 | 13.6 | 80 |
| 98 | 84 | 14 | 81 |
| 99 | 85 | 14.1 | 84 |
| 100 | 86 | 14.2 | 85 |
| 101 | 87 | 14.3 | 86 |
| 102 | 88 | 14.4 | 87 |