Size and fit guide
School backpacks for kids: the right size and fit by age
Most children aged 3 to 10 are well served by a school backpack of about 10 litres that takes A4 flat, sits between the shoulders and the waist, and has adjustable shoulder straps plus a chest strap that moves up and down as they grow.
Updated
A school backpack is bought once and used every day, so getting the size and fit right matters more than anything else. Too big and it gets overfilled and bumps the back of the knees; too small and the reading folder goes in at an angle.
This page covers size and fit by age, what really fits inside, and how to adjust the straps. For how a bag keeps the rain out, see our waterproof kids backpack page.
A 3-year-old vs a 7-year-old
A 3-year-old at nursery carries a change of clothes, a snack, a 500 ml bottle and perhaps a small folder. The bag should sit high on a short back and be light enough that they will carry it themselves.
A 7-year-old at primary school carries a reading folder, A4 workbooks, a lunch box, a bottle and a jumper, and on some days PE kit. The same 10 litres still works, because the depth lets a lunch box sit beside the folder rather than on top of it.
- Ages 3 to 5: about 10 litres. Spare clothes, snacks, bottle, nursery folder.
- Ages 5 to 10: about 10 litres, taking A4 flat. Reading folder, workbooks, lunch box, bottle, jumper.
- Ages 11 and up: 15 litres and above, because textbooks and a laptop change the maths.
Capacity and the size that takes A4 flat
A4 paper is 29.7 cm by 21 cm, so a backpack needs at least about 31 cm of internal height and 23 cm of internal width before a folder will lie flat. Litres alone mislead: two 10 litre bags can be shaped completely differently.
plop is 10 litres with the roll top closed and measures 33 cm high, 26 cm wide and 15 cm deep, so A4 sits flat with room beside it.
What fits inside a 10L plop
A4 books, spare clothes, a lunch box and a 500 ml bottle, plus a few small essentials like sticks, snacks and socks. Inside there is a small pouch at the back and a name label for the cloakroom.
Strap length and fit
A loaded backpack should sit between the shoulders and the waist, never below the bottom, be no wider than the child's shoulders, and weigh no more than roughly a tenth of the child's body weight.
Shorten the padded shoulder straps until the top of the bag sits just below the shoulders, then slide the chest strap up or down so it crosses the chest at the right height and clip it. Re-check the straps each term as they grow.
- Top of the bag just below the shoulders.
- Base above the waist, not hanging on the bottom.
- Chest strap across the chest, moved up or down to fit.
Keeping the contents dry
Size and fit are only half the decision for a daily walk to school. Our waterproof kids backpack page explains the roll top, welded seams and reinforced base that keep a reading folder dry.
Common questions
- What size school backpack does a child need?
- Around 10 litres for ages 3 to 10, with at least about 31 cm by 23 cm inside so A4 lies flat. plop is 33 x 26 x 15 cm.
- Is a 10L backpack big enough for a 7 year old?
- Usually yes. 10 litres takes A4 books, a lunch box, a 500 ml bottle and a jumper. Older children carrying textbooks or a laptop need 15 litres and up.
- Is a 10L backpack too big for a 3 year old?
- Not if it sits high on the back and the straps are shortened. Pack only what nursery needs so it stays light.
- How should a child's backpack straps be adjusted?
- Shorten the shoulder straps so the bag sits between the shoulders and the waist, then slide the chest strap up or down to cross the chest and clip it.
- How heavy should a child's school backpack be?
- No more than about a tenth of the child's body weight once it is loaded.