Pregnancy week by week
Each week has its own page: what is developing, what usually happens at appointments around then, and one specific, useful thing the partner can do. Every clinical detail is attributed to the ACOG or NHS patient material it came from, and last checked on 2026-07-30.
Five of the 42 weeks - 1, 2, 3, 41, 42 - carry no published length, and those pages say so instead of borrowing a figure from somewhere else. That is the whole editorial policy of this section in one sentence.
First trimester (weeks 1-13)
Second trimester (weeks 14-27)
Third trimester (weeks 28-42)
| Week | Published figure | Measured | Comparison |
|---|---|---|---|
| 1 | not published | - | - |
| 2 | not published | - | - |
| 3 | not published | - | - |
| 4 | 2 mm | head to bottom | about the size of a poppy seed |
| 5 | 2 mm | head to bottom | about the size of a sesame seed |
| 6 | 6 mm | head to bottom | about the size and shape of a pea |
| 7 | 10 mm | head to bottom | about the size of a grape |
| 8 | 16 mm | head to bottom | about the size of a raspberry |
| 9 | 22 mm | head to bottom | about the size of a strawberry |
| 10 | 30 mm | head to bottom | about the size of a small apricot |
| 11 | 41 mm | head to bottom | about the size of a fig |
| 12 | 5.4 cm | head to bottom | about the size of a plum |
| 13 | 7.4 cm | head to bottom | about the size of a peach |
| 14 | 8.5 cm | head to bottom | about the size of a kiwi fruit |
| 15 | 10.1 cm | head to bottom | about the size of an apple |
| 16 | 11.6 cm | head to bottom | about the size of an avocado |
| 17 | 12 cm | head to bottom | about the size of a pomegranate |
| 18 | 14.2 cm | head to bottom | about the size of a bell pepper |
| 19 | 15.3 cm | head to bottom | about the size of a beef tomato |
| 20 | 25.6 cm | head to heel | about the size of a banana |
| 21 | 26.7 cm | head to toe | about the size of a carrot |
| 22 | 27.8 cm | head to toe | about the size of a sweet potato |
| 23 | 28.9 cm | head to heel | about the size of a large mango |
| 24 | 30 cm | head to heel | about the size of a corn on the cob |
| 25 | 34.6 cm | head to heel | about the size of a courgette |
| 26 | 35.6 cm | head to heel | about the size of a cucumber |
| 27 | 36.6 cm | head to heel | about the size of a head of cauliflower |
| 28 | 37.6 cm | head to heel | about the size of an aubergine |
| 29 | 38.6 cm | head to heel | about the size of a butternut squash |
| 30 | 39.9 cm | head to heel | about the size of a cabbage |
| 31 | 41.1 cm | head to heel | about the size and weight of a coconut |
| 32 | 42.4 cm | head to heel | about the same length as a bunch of celery |
| 33 | 43.7 cm | head to heel | about the size of a pineapple |
| 34 | 45 cm | head to heel | about the size of a cantaloupe melon |
| 35 | 46.2 cm | head to heel | about the size of a honeydew melon |
| 36 | 47.4 cm | head to heel | about the size of a romaine lettuce |
| 37 | 48.6 cm | head to heel | about the length of a leek |
| 38 | 49.8 cm | head to heel | about the length of a stick of rhubarb |
| 39 | 50.7 cm | head to heel | about the size of a watermelon |
| 40 | 51.2 cm | head to heel | about the size of a pumpkin |
| 41 | 3 to 4 kg (weight, no length published) | - | - |
| 42 | not published | - | - |
The rest of the wing
- Due date calculatorThe 280-day convention, with the five-week term window beside it
- Baby name generatorFilters real ONS name data - and stores no invented meanings
- Baby cost calculatorPublished first-year figures, each with its own currency year
- Registry checklistThe NHS newborn list, with the quantities it actually gives
Everything you type here is computed in your browser. Nothing you enter is stored on a server, sent anywhere, or shared — there is no account and no health data to leak.
The sources these weeks defer to
- NHS, Week-by-week guide to pregnancy — week-by-week development, weeks 4 to 41
- NHS: your antenatal appointments — the appointment schedule these pages follow
- ACOG Committee Opinion 700: Methods for Estimating the Due Date — gestational age, the 280-day convention and the 37-42 week term window
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