This chart outlines expected ultrasound measurements (in mm) based on weeks gestation.

BPD=biparietal diameter (the diameter between the 2 sides of the head

HC=head circumference

AC=abdominal circumference

FL=femur length

Hadlock Formulas: Haddlock Radiology 1984; 152: 497-501

Weeks BPD (mm) HC (mm) AC (mm) FL
(mm)
16 32.3 124.4 99.1 20.5
16.5 34.2 131.2 105.5 22.1
17 36.0 137.9 111.9 23.7
17.5 37.7 144.5 118.2 25.2
18 39.5 151.1 124.5 26.7
18.5 41.3 157.7 130.7 28.3
19 43.0 164.1 136.9 29.8
19.5 44.7 170.5 143.0 31.2
20 46.4 176.8 149.1 32.7
20.5 48.1 183.0 155.1 34.1
21 49.7 189.2 161.1 35.6
21.5 51.4 195.3 167.0 37.0
22 53.0 201.3 172.9 38.4
22.5 54.6 207.2 178.7 39.8
23 56.2 213.0 184.5 41.1
23.5 57.8 218.7 190.2 42.5
24 59.3 224.4 195.9 43.8
24.5 60.8 229.9 201.5 45.1
25 62.3 235.4 207.1 46.4
25.5 63.8 240.8 212.7 47.7
26 65.3 246.0 218.1 48.9
26.5 66.7 251.2 223.6 50.2
27 68.1 256.2 228.9 51.4
27.5 69.5 261.2 234.3 52.6
28 70.8 266.1 239.6 53.8
28.5 72.2 270.8 244.8 55.0
29 73.5 275.5 250.0 56.1
29.5 74.7 280.0 255.1 57.3
30 76.0 284.4 260.2 58.4
30.5 77.2 288.7 265.2 59.5
31 78.4 292.9 270.2 60.6
31.5 79.6 297.0 275.1 61.7
32 80.7 300.9 280.0 62.7
32.5 81.9 304.7 284.8 63.8
33 82.9 308.4 289.6 64.8
33.5 84.0 312.0 294.3 65.8
34 85.0 315.5 299.0 66.8
34.5 86.0 318.8 303.7 67.7
35 87.0 322.0 308.2 68.7
35.5 87.9 325.0 312.8 69.6
36 88.8 327.9 317.3 70.6
36.5 89.7 330.7 321.7 71.5
37 90.5 333.3 326.1 72.3
37.5 91.3 335.8 330.4 73.2
38 92.1 338.2 334.7 74.1
38.5 92.8 340.4 338.9 74.9
39 93.5 342.5 343.1 75.7
39.5 94.2 344.4 347.2 76.5
40 94.8 346.1 351.3 77.3
40.5 95.4 347.7 355.4 78.1
41 95.9 349.2 359.3 78.8
41.5 96.5 350.5 363.3 79.5
42 96.9 351.6 367.2 80.3