How diaper.best compares diapers

Everything in millimetres

Each product's dimensions, about twenty of them (total length, the widths at the front, crotch and back, the wings, the absorbent core, the height of the leak guards), are stored as whole millimetres. They are taken from a fixed point: the centre of the crotch. Measured from there, two products line up crotch to crotch, so you can see where one is longer, wider or narrower than the other.

Why the size label misleads

"M" and "L" are labels, not measurements. Each brand draws its own lines between sizes, so one brand's large can be cut for the hips of another brand's medium, and the same letter covers different bodies from one line to the next. What many brands do print is the hip range a size is made for. That range is what diaper.best compares.

Fit by hip measurement

Enter your hip circumference (in centimetres or inches) and the list keeps the products whose range includes it. Where a brand prints only a waist range for a size, the waist range stands in; products with neither are left out, because nothing says whom they fit.

Within a size's range, the middle counts most. If your measurement falls in the middle 30–70 % of the range, the fit bar says Good fit; nearer the lower end it says likely loose, nearer the upper end likely tight. For a range of 80–120 cm, the good-fit zone runs from 92 to 108 cm. The list puts the good fits first, then the rest of the ranges, then sizes that do not contain your hip.

Within each of those groups the products are ranked on a bell curve. Each size's range is read as a bell: the middle of the range at the top, the printed limits two standard deviations out. Your score is the height of the bell where your measurement falls. A bell over a narrow range is taller than one spread over a wide range, so a size cut for fewer bodies wins over a one-size-fits-many range that also contains you: it is more likely to be cut for yours.

What the capacity figures mean

Packs and shops quote capacity in different ways, and the numbers are not interchangeable:

• ISO: the total capacity under ISO 11948-1 (the Rothwell method), from the manufacturer's specification. The whole product soaks in salt water, drains and is weighed: what the core can hold at most.
• Before leakage: DIN 13222, a German test that puts the product on a test torso and adds liquid until it leaks. German health insurers require it for the products they list.
• Practical: the manufacturer's own working figure for what the product holds in use. We count it on the same scale as the before-leakage test.
• Marketed: any other single figure a brand or shop advertises, the least reliable of them all.

The two tests are far apart. Across 280 products whose makers publish both figures, a product held about a third of its ISO total before it leaked, and a smaller share the bigger the product: about 33 % at 1,500 ml, 28 % at 5,150 ml. A likely reason is that liquid leaks out before it has spread through a large core.

diaper.best compares on two numbers. Capacity is the figure the maker publishes, the ISO total or the marketed one, whichever is larger, and says which kind it is; we never change it. A product that publishes only a practical figure gets an ISO equivalent calculated from it, marked with a *. Approximated real-life capacity is the before-leakage test where the maker publishes it, else the maker's practical figure, else approximated from the published ISO total or marketed figure with the curve and marked with a *.

Many diapers sold for adults who wear them by choice are rated far above 7,000 ml. Those figures are mostly worked out from the absorbent materials, some in distilled water, rather than tested: against independent tests they run about 1.6 times the ISO scale. For the real-life approximation such a figure counts at a 1.6th; the published figure stays as it is. The capacity sort, the price per litre and the real-life sort use these numbers.

Calculated figures are a theory, not a measurement. The curve is typically within 12 % of a product's real test result, and one product in ten is more than 30 % off. What a diaper holds on a body depends on far more than either lab test: fit, body position, how fast and how often, and whether you sit, sleep or move. A calculated figure is a starting point for comparing products, nothing more.

Where the ratings come from

Ratings come from people who have worn the products: ratings given on diaper.best and reviews gathered from public forums, where one comment counts as one vote per product it talks about. Products are rated from 0.5 to 5 stars, in half steps, in nine categories: sizing, absorption capacity, absorption speed, adhesives, production quality, shell material, design, looks and performance. Ratings that depend on size also record the rater's hip measurement. Two scales sit beside the stars: how loud the diaper crinkles and whether the cut runs small or big. They describe the product rather than grade it.

A product's ratings are pooled with its close relatives where the answer would be the same: the other sizes of the same line share what does not depend on size (adhesives, absorption speed, shell, production quality, design, looks), and other prints on the same build share the construction categories. Sizing, capacity and performance always stay with the product itself.

Prices and shipping

Prices are shown as each shop shows them. Tax is charged by the shop: within the EU it depends on your delivery country, in the US and Canada it is usually added at checkout, so the final price can differ slightly. Other currencies are converted at the ECB rate.

A product counts as available in your country only when a shop we track sells it and ships there, by the shop's own stated delivery area. The value ranking compares the cheapest price per litre of capacity among those shops, in your currency, so it can differ from one country to the next.

Try it with your own measurement

The comparison is only as good as the measurement you give it. Measure around the widest part of your hips and enter it on the start page, or open a list for a 105 cm hip to see how it works: diapers that fit a 105 cm hip. Every other filter is under "More filters" on the start page.