Nappy size and cost calculator
Enter your baby's weight, their date of birth and what you pay for a pack. The tool gives the right nappy size in your own country's numbering, how many changes a day to expect, and what that costs a week, a month and to the end of nappies.
Nappy size and cost calculator
No sign-up · PrivateNappies are sized by weight, never by age. Use the most recent weight from the red book, the well-child book or the clinic.
Used only to work out how many changes a day to expect — a newborn goes through nearly twice as many as a one-year-old.
Optional. Whatever you actually pay, in your own currency. Leave it blank if you only want the size.
The number on the front of the pack.
Optional. If you are weighing up reusables, put the up-front cost of the set here and this tool works out the week the two lines cross.
Enter your baby’s weight. Nappies are sized by weight, and the size numbers do not mean the same thing in every country.
Nothing you type leaves your device. The whole calculation runs in your browser.
How this is calculated
FormulaHow the size and the cost are worked out
Size comes from weight, never age, matched against the published chart for your market. Where several bands contain your baby's weight — and they overlap heavily — the tool picks the largest band in which your baby still sits in the lower-middle of the range, so there is room to grow, and falls back to the smallest containing band for a newborn.
Cost = price per pack ÷ nappies per pack × changes a day × the period. The lifetime projection adds the months up one at a time using the change rate for each age rather than applying today's rate to the whole of childhood.
The charts, and the trap in them
Pampers UK, in kilograms: size 0 under 3, size 1 is 2–5, size 2 is 4–8, size 3 is 6–10, size 4 is 9–14, size 5 is 11–16, size 6 is 13–18, size 7 is 15 and over.
Pampers US, in pounds: N under 10, size 1 is 8–14, size 2 is 10–22, size 3 is 13–26, size 4 is 15–34, size 5 is 20–37, size 6 is 23–44, size 7 is 26–50, size 8 is 30 and over.
Huggies Australia, in kilograms, labelled by stage as well as number: 1 Newborn up to 5, 2 Infant 4–8, 3 Crawler 6–11, 4 Toddler 10–15, 5 Walker 13–18.
Now compare. UK size 4 is 9–14 kg. US size 4 is 15–34 lb, which is 6.8–15.4 kg. Same brand, same digit, a baby more than two kilos apart. A chart from an American site will put a British baby in the wrong nappy.
Changes a day
Two NHS figures anchor the model: “small babies might need up to 10 or 12 changes a day” and “older babies need around 6 to 8 changes”. Pampers gives 8–12 a day for a newborn and roughly 250–300 a month, which is the same figure said differently. The bands between the two anchors are a straight taper between them and the tool labels them as exactly that, because no published figure exists for four-month-olds specifically.
The number on the pack is not an international standard
Nappy sizes look like a universal system. They are not. Pampers publishes size 4 in the United Kingdom for babies of 9 to 14 kilograms. Pampers publishes size 4 in the United States for 15 to 34 pounds — 6.8 to 15.4 kilograms. Same brand, same digit, and the American size 4 starts on a baby more than two kilos lighter.
Australia does something more honest and labels by stage as well as number: 1 Newborn, 2 Infant, 3 Crawler, 4 Toddler, 5 Walker, with the weight range printed alongside. At least there the word tells you what the number means.
So if you have moved country, or are following advice from a site written somewhere else, and the size you were told does not fit, this is why. Nappies are sized by weight, and the weight bands are national.
Fit beats the chart
Every chart overlaps deliberately, because babies of the same weight are different shapes. A seven-kilogram baby is legitimately in a UK size 2, 3 or 4 depending on build, and the way to choose is to look at the nappy rather than the number.
Signs you are in the right size: the waistband is snug without leaving a red mark, there is no gap around the legs, and two fingers slide comfortably under each leg cuff. Signs to move up: leaks up the back, tabs pulling to the very end of their travel, red marks at the waist or on the thighs.
Sizing up too early causes leaks just as reliably as leaving it too late, because a loose nappy has gaps. If you have gone up and the leaks got worse, go back down.
How many you will actually get through
More than you expect at the start and fewer than you fear later. The NHS says small babies might need up to 10 or 12 changes a day, and older babies around 6 to 8. Pampers puts a newborn at 8 to 12 a day, or roughly 250 to 300 a month.
The rule underneath both is simple: change whenever your baby has done a wee or a poo. That is what prevents nappy rash, and it is why the newborn figure is so high — a newborn feeds constantly and the two ends are connected. Always put a fresh nappy on at bedtime, because that is the one that stays on longest.
Do not buy a mountain of the smallest size
Newborn nappies fit for weeks, sometimes days, and a big baby can skip the size entirely. Buy one pack, see how it goes, then stock up on the size after — that is the one your baby will stay in longest, and it is the one worth buying in bulk or on subscription.
If you are given nappies as a present, ask for size 3 and up. Everyone buys newborn.
Reusables, honestly
The arithmetic is straightforward and usually favours reusables, especially across more than one child. Put the up-front cost of a set into the tool and it will tell you the week the two lines cross, using your own price per disposable and your baby's current change rate.
Two caveats the arithmetic leaves out, and they cut in opposite directions. It ignores washing — water, electricity and detergent are real and are not zero. And it flatters disposables by ignoring resale, because a reusable set holds value and can be sold on or used again for a second child, while a used disposable cannot. Many local councils in the UK run voucher or trial schemes; it is worth checking yours before you buy a full set.
Nobody can tell you when nappies stop
This is the largest uncertainty in the whole calculation, which is why the tool shows you three totals rather than one. CDC's parenting guidance is that most children “are not able to toilet train until 2 to 3 years old”, and that starting before a child is ready causes stress and setbacks that make training take longer.
A year either way is a lot of money, and it is not a year you can plan. Anyone quoting you a single confident lifetime nappy bill has picked an end date out of the air.
Where nappies sit in the wider bill
Large, steady and much smaller than childcare. For most families nappies are somewhere between a few hundred and a couple of thousand across the whole of nappy-wearing life, while childcare and lost earnings run to five figures in the first year alone. It is worth optimising, but it is not where the money is. Our cost of a baby's first year calculator puts the whole thing in proportion, and will take your weekly nappy figure straight from here.
Sources
- Pampers nappy size and type guide — Pampers UK, accessed
- Pampers baby diaper size chart guide — Pampers US, accessed
- How many newborn nappies do you need? — Pampers UK, accessed
- Changing a nappy — NHS Start for Life, accessed
- What you can do for your 18-month-old (toilet training readiness) — Centers for Disease Control and Prevention, accessed