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Diaper Size Calculator

The right nappy size for your baby's weight, how many you'll use, and when to size up.

Related tools

All Practical tools →
Clothing size converterTops, bottoms and shirt collars converted separately between FR, IT, DE, UK and US — each with the body measurement EN 13402 makes its primary dimension.Shoe size converterEU, UK, US and Japanese shoe sizes side by side for women and men, each row tied to the foot length in millimetres — the one figure that does not change from brand to brand.Commute Life Wasted CalculatorSee how many hours, full days and years of your life your commute adds up to — and what you could have done instead.Dew Point CalculatorDew point from air temperature and relative humidity (Magnus formula), with a comfort band.Dishwasher Load OptimizerEnter what needs washing to see how many cycles you need and whether the next load is full enough to run.Gift Idea GeneratorRanks a hand-written library of 170 gift ideas against who you are buying for, the occasion, your budget and the interests you type in, and tells you why each one came out on top. A curated library with a scoring rule, not a language model — the same answers come back every time.Meeting Cost TickerWatch the real-time cost of a meeting tick up from attendee count and hourly rates, with per-person and projected totals.Polite Excuse GeneratorWrites several ready-to-send ways to say no, composed from hand-written sentence banks and varied by who you are answering, the tone you pick and how much you want to reveal. A curated composer, not a model — the same choices reproduce the same set, and a reshuffle draws a new one.

Diaper Size Calculator is free to use as often as you like, directly from this page. It sits under Practical in our catalogue, alongside Clothing size converter and Shoe size converter.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Diaper Size Calculator?

The right nappy size for your baby's weight, how many you'll use, and when to size up.

When would I actually use this?

The questions no reference answers: what a meeting is costing while it runs, how many hours a commute has taken out of a year, how much detergent a load actually needs, and a few that exist for the pleasure of knowing — how many popcorn kernels would fill a room, what a hamster generates.

What is the most common mistake?

Quoting the playful ones as if they were measurements. A room filled with popcorn and a salary counted in bathroom breaks are arithmetic done honestly on premises chosen for fun; the number that comes out is exactly as solid as the assumption you fed it, which is the joke.

How is Diaper Size Calculator different from Clothing size converter?

They sit next to each other but answer different questions: Clothing size converter is the one to open when you need it to tops, bottoms and shirt collars converted separately between FR, IT, DE, UK and US — each with the body measurement EN 13402 makes its primary dimension. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Shoe size converter is the closest one after this: EU, UK, US and Japanese shoe sizes side by side for women and men, each row tied to the foot length in millimetres — the one figure that does not change from brand to brand.

What else is worth having open alongside it?

Commute Life Wasted Calculator and Dew Point Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The household ones follow the figure printed on the packet or the manufacturer's chart, which is why a detergent dose or a nappy size may not match another brand's. The rest state their assumptions on the page, because assumptions are the whole content of the answer.

Further reading

All guides →
How-toHow Much Laundry Detergent to Use: Load Size First, Water Hardness SecondA normal medium load in a high-efficiency machine works out at 37 ml. Load size swings that threefold; water hardness only 1.28-fold — and the tool's hardness input carries no units at all. Here are the scales and the conversions it leaves out.ExplainerDew Point: What It Is, and How the Calculator Gets ItMagnus–Tetens with the Alduchov–Eskridge coefficients, 17.625 and 243.04. Why an absolute number beats relative humidity for judging comfort, what temperature a window has to reach before it runs, and the one input the calculator does not check.GuideWhat a Meeting Costs the Company, and What the Number Is ForSalary is not the cost. The ticker applies no loaded-cost multiplier of its own, so the rate box is where you have to put it. And the number is for one comparison: a recurring meeting against the written update that would replace it.ExplainerWind Chill: What the “Feels Like” Number Actually MeasuresThe calculator runs the 2001 index, not the 1945 one, and refuses to answer above 50 °F or under 3 mph. Here is what its number is a model of — bare skin, in shade, walking — and the two things it says nothing about: a clothed body, and a parked car.ComparisonWhich Fishing Knot Holds Best, and Why Every Published Table DisagreesKnot strength is quoted as a percentage of the line's rated breaking strain, and the percentages in circulation come from tests nobody agrees on. What the calculator on this page really stores, what one peer-reviewed measurement actually found, where a line breaks and why, and how to match a knot to its job.ExplainerWhat Remote Work Actually Saves, Once Heating Is CountedThe heating bill is real and it is small — about a fifteenth of the fuel a car commuter stops burning. The balance only goes negative in three identifiable cases, and one of them is a season ticket. Priced from Eurostat energy data, with the German tax system pushing the other way.