Baby size by week, without the fruit
Why do pregnancy apps compare a baby to fruit?
Convention, mostly. Fruit is familiar and it sounds warm, but it is a poor ruler for the one job it has: produce is not a standard size. A mango can be 8 cm or 15 cm and both are mangoes, so two weeks that sound a fortnight apart can be the same length. Every object in the eight sets below has a published measurement instead.
A ruler has to be a fixed length
That is the whole problem with produce. A credit card is 85.6 mm because ISO/IEC 7810 says so, and every credit card on earth is that size. A mango is whatever size that mango grew to. When the ruler moves, the comparison stops meaning anything: two weeks that sound a fortnight apart can be the same published length, and nobody reading can tell.
The second problem is recognition. A comparison only works if you already know how big the object is, and the fruit lists run out of familiar produce around the middle weeks, which is when they start reaching for a rutabaga or an heirloom tomato. Being told your baby is the size of something you would have to look up is not a comparison, it is a second question.
What we use instead
Eight sets, because the ruler somebody wants is a matter of taste while the length is not. Someone who has never held a rutabaga has definitely held a phone, a basketball, a Freddo Frog or a game controller. Each set covers all 37 weeks from 4 to 40, and every object carries the dimension its measurement refers to, so the claim is checkable rather than decorative.
The measurements are held against the published NHS length for that week in our test suite, which means a comparison here can be funny or it can be wrong, and never both. That is not a claim other size charts make, because most of them are copied rather than measured.
The eight rulers
Each one is shown at week 24 below, roughly the middle of a pregnancy. Where the figures come from is stated for every set, because a reader who wants to know why a twelve-inch pizza is 30.5 cm is entitled to the answer.
Sweet treats
The lolly aisle, scaled up week by week.
Week 24: a hollow chocolate Santa, 30 cm hat to boots
Typical retail sizes for confectionery and baking: a four-finger Kit Kat is 10.5 cm end to end, a Freddo 5.5 cm, and the Toblerone they sell at duty-free a genuine 26 cm.
Australian animals
From a green ant to a red-tailed black cockatoo.
Week 24: a sugar glider, tail included, 32 cm nose to tail tip
Head-and-body or beak-to-tail lengths as field guides publish them. Where a species spans a range, the figure is a typical adult rather than the largest one anybody has measured.
The 90s
Everything that was on your bedroom floor in 1997.
Week 24: Buzz Lightyear, 30.5 cm head to boots
Retail dimensions of the actual products: a Game Boy is 148 mm tall, a Tamagotchi 55 mm, a cassette 102 mm, a Nokia 3310 113 mm.
Sport
Regulation balls, bats and everything else with a rulebook.
Week 24: a boxing glove, 30 cm cuff to knuckles
Match-regulation equipment sizes: a golf ball is 42.67 mm across at the legal minimum, a shuttlecock 85 mm end to end, a basketball hoop 45.7 cm, an Olympic weight plate 45 cm.
Things you already own
The stuff already in your house — a credit card, a dinner plate, a 30 cm ruler.
Week 24: a 30 cm ruler, 30 cm end to end
Everyday objects at their standard or typical size: a credit card is 85.6 mm under the ISO/IEC 7810 ID-1 standard, an Australian 50-cent coin 31.6 mm across the flats, a school ruler exactly what it says on it.
Gaming
Controllers, consoles and the cartridges you had to blow on.
Week 24: an Xbox Series X, 30.1 cm top to bottom
Manufacturer dimensions: a Nintendo Switch is 242 mm wide with the Joy-Cons on, a PlayStation 5 390 mm standing up, an Xbox Series X 301 mm.
Fast food
The drive-through menu, in ascending order.
Week 24: a twelve-inch pizza, 30.5 cm across
Menu-standard sizes, which are mostly just inches wearing a hat: a twelve-inch pizza is 30.5 cm across because twelve inches is 30.5 cm.
Toys
The toybox you are about to start filling.
Week 24: Buzz Lightyear, 30.5 cm head to boots
Boxed retail sizes: a Lego minifigure is 4 cm head to feet, a Barbie 29.2 cm, a Buzz Lightyear 30.5 cm.
The same six weeks, in every set
| Week | Published length | Sweet treats | Australian animals | The 90s | Sport | Things you already own | Gaming | Fast food | Toys |
|---|---|---|---|---|---|---|---|---|---|
| Week 8 | 1.6 cm long, from head to bottom | a Malteser | a bull ant | a Polly Pocket doll | a golf tee's head | a dice | a thumbstick cap | a bendy straw's concertina | a marble |
| Week 12 | 5.4 cm long, from head to bottom | a Freddo Frog | a witchetty grub | a Tamagotchi | a golf tee | an AirPods case | a Game Boy Advance cartridge | a doughnut hole | a plastic army man |
| Week 20 | 25.6 cm long, from head to heel | the giant Toblerone from duty-free | a rainbow lorikeet | a Bop It | a basketball | a dinner plate | a Nintendo Switch, Joy-Cons on | a slice of large pizza | a small teddy bear |
| Week 24 | 30 cm long, from head to heel | a hollow chocolate Santa | a sugar glider, tail included | Buzz Lightyear | a boxing glove | a 30 cm ruler | an Xbox Series X | a twelve-inch pizza | Buzz Lightyear |
| Week 32 | 42.4 cm long, from head to heel | a wedding cake tier | an echidna | a Sit'n Spin | a basketball hoop's rim | a record player | a twenty-inch monitor | a party sub platter | a large teddy bear |
| Week 40 | 51.2 cm long, from head to heel | the sweetest thing you will ever make | a newborn human, the least camouflaged mammal on the continent | a 51.2 cm original, no reissue | a debutant, yet to be selected for anything | a newborn baby | a new player, entering the game | the only takeaway worth a nine-month wait | the only toy that plays back |
Lengths are the figures the NHS publishes for each week. Up to week 19 a baby is measured from head to bottom; from week 20 it is head to heel, which is why the published length jumps between those two weeks.
Every week, all eight rulers
Each week has its own page showing all eight sets side by side, along with what is developing then and how many months it is.
Questions about baby size comparisons
- What is wrong with the fruit size comparison?
- Two things. Produce has no standard size, so the comparison moves depending on which mango you are picturing, and a chart built on it cannot be checked against anything. And a comparison only works if the reader already knows how big the object is — which is why the lists reach for a rutabaga or a heirloom tomato around the weeks where nothing common is the right length. The ruler has to be something you can picture without looking it up.
- What does BubSync use instead of fruit?
- Eight sets, and you pick: sweet treats, australian animals, the 90s, sport, things you already own, gaming, fast food, toys. Each one covers all 37 weeks from 4 to 40, and each object is measured to a published standard — a credit card is 85.6 mm under ISO/IEC 7810, a twelve-inch pizza is 30.5 cm because twelve inches is 30.5 cm, an Xbox Series X is 301 mm because Microsoft says so.
- Are the comparisons actually accurate?
- Every object carries the dimension its measurement refers to, so the claim is checkable rather than decorative, and the whole set is held against the NHS published length for that week in the test suite. A comparison here can be funny or it can be wrong, and never both. The lengths themselves are population averages published by the NHS, not a measurement of any particular baby.
- Can I change the ruler?
- Yes, on the calculator, and the choice follows you: the week-by-week chart below it switches to the same set. Each week also has its own page showing all eight at once, so you can compare rulers for the week you are actually in without choosing first.
Where these numbers come from
- NHS — Week-by-week guide to pregnancy — The published length of a baby at each week of pregnancy — measured head to bottom until week 20 and head to heel from week 20 — and what is developing at that stage.
- Pregnancy, Birth and Baby — Pregnancy week by week — The Australian Government health service’s week-by-week account of how a pregnancy is counted and what develops at each stage.
Stop doing this maths in your head
Once the counting turns into feeds, sleeps and nappies, BubSync keeps that record shared across everyone caring for your baby.
