Quick answer: a newborn's foot is about 3.3 inches long, a 6-month-old's about 4.1 inches, a 12-month-old's about 4.75 inches, and a 24-month-old's about 5.5 inches. In US shoe sizes that's roughly a 0 at birth, a 3 at 6 months, a 5 at a year, and a 7 at two. The month-by-month chart below gives the average foot length and matching size for every month in the first year and every three months in the second, plus the Grookz size that covers it. Measure the foot before you buy if you can; the measuring guide takes two minutes.
Baby shoe size chart by month
| Age | Average foot length | US size | Grookz size |
|---|---|---|---|
| Newborn | 3.3 in / 8.4 cm | 0 to 1 | Size 1 (0 to 6 months) |
| 1 month | 3.5 in / 8.9 cm | 1 | Size 1 |
| 2 months | 3.6 in / 9.1 cm | 1 | Size 1 |
| 3 months | 3.75 in / 9.5 cm | 2 | Size 1 |
| 4 months | 3.9 in / 9.9 cm | 2 | Size 1 |
| 5 months | 4.0 in / 10.2 cm | 2 to 3 | Size 1 |
| 6 months | 4.1 in / 10.4 cm | 3 | Size 1 |
| 7 months | 4.25 in / 10.8 cm | 3 | Size 2 (7 to 12 months) |
| 8 months | 4.4 in / 11.2 cm | 3 to 4 | Size 2 |
| 9 months | 4.5 in / 11.4 cm | 4 | Size 2 |
| 10 months | 4.6 in / 11.7 cm | 4 | Size 2 |
| 11 months | 4.7 in / 11.9 cm | 4 to 5 | Size 2 |
| 12 months | 4.75 in / 12.1 cm | 5 | Size 2 |
| 15 months | 5.0 in / 12.7 cm | 5 | Size 3 (13 to 18 months) |
| 18 months | 5.1 in / 13 cm | 6 | Size 3 |
| 21 months | 5.4 in / 13.7 cm | 6 to 7 | Size 4 (19 to 24 months) |
| 24 months | 5.5 in / 14 cm | 7 | Size 4 |
These are averages. A big baby can run a full size ahead of the chart and a small one a full size behind, and both are normal. The number that matters is the foot length, which is why the size finder asks for a measurement rather than a birthday.
How baby feet grow, month by month
Feet grow fastest in the first year, about half a size every two months, and the growth comes in spurts rather than a steady line. A baby can stay in one size for ten weeks and then jump a full size in three. From 12 to 24 months the pace slows to roughly half a size every three months, and from two to three years to about half a size every four months.
Two practical consequences. First, don't stock up: a pair bought two sizes ahead for next season may never fit at the right time of year. Second, re-check the fit every six to eight weeks in the first two years, because a shoe that fit in September can be pinching by November.
By month: what each stage needs
0 to 3 months
Nothing with a sole. Newborn feet need warmth, not protection, and the bones are still mostly cartilage. Socks, footed sleepers, or a soft sock shoe for the ones who kick socks off. Our newborn shoe size post covers this stretch, including what size to buy as a gift.
4 to 6 months
Rolling, grabbing feet, maybe sitting. Still no need for shoes. If you want something for photos or cold floors, a Size 1 sock shoe fits a foot up to 4.5 inches and stays on better than socks.
7 to 9 months
Crawling, and the first time grip matters. Knees and feet slide on hardwood and tile, and a sock shoe with a rubber sole fixes that without changing how the foot moves. Most babies move into Size 2 around 7 months. See the 7-month and 9-month posts for details.
10 to 12 months
Pulling up and cruising along furniture, sometimes first steps. Barefoot is still best for learning to balance indoors; a thin-soled sock shoe is the next best thing on slippery floors. The 1-year-old post covers fitting a first real shoe.
13 to 18 months
Walking, then walking outside, which is when a sole that protects against gravel and hot pavement earns its place. Feet are around 5 inches, a Grookz Size 3. The 18-month post has the fitting details.
19 to 24 months
Running, climbing, and strong opinions about shoes. Feet are 5.25 to 5.5 inches, a Size 4. Sock shoes still work for daycare and indoors; for playgrounds, a firmer first walker.
Measuring a baby who won't hold still
Measure standing if you can, since feet spread under weight. For a baby who can't stand yet, hold the foot flat against a hard book, mark heel and longest toe on a strip of paper, and measure the strip. For a toddler who won't cooperate, trace the foot while they're asleep or in the high chair, or measure the insole of a shoe that fits well and add half an inch. The measuring guide walks through all three.
Signs it's time for the next size
- Red marks on the toes, top of the foot, or heel after wearing
- Toes curled or pressed against the end (press the toe box while the baby stands)
- A sock shoe that's suddenly hard to pull over the heel
- A baby who starts pulling at shoes they used to leave alone
- The heel slipping out of a hard-soled shoe is the opposite problem: too big, or not fastened
For the full newborn-to-3-years table with EU and UK sizes, see the baby shoe size chart by age.
Frequently asked questions
What size shoe does a 3-month-old wear?
About a US size 2, for a foot around 3.75 inches. In Grookz sizing that's Size 1, which covers newborn to 6 months. Most 3-month-olds don't need shoes.
What size shoe does a 6-month-old wear?
Usually a US size 3, for a foot around 4.1 inches. That's still Grookz Size 1; most babies move to Size 2 around 7 months or when the foot passes 4.5 inches.
What size shoe does a 9-month-old wear?
Typically a US size 4, for a foot around 4.5 inches, which is Grookz Size 2 (7 to 12 months).
How many shoe sizes do babies go through in the first year?
Four or five, from a size 0 or 1 at birth to a size 4 or 5 by the first birthday. Sock shoes stretch across two to three of those sizes, so most families buy two sizes in the first year rather than five.
Is it better to buy baby shoes a size bigger?
Half a size bigger, leaving about half an inch of room, is right. A full size or more makes a new walker trip and lets the heel slip.
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