Frequently asked questions
The short versions. The methodology page has the long ones.
- Why is period underwear sizing so inconsistent between brands?
- Each brand drafts its own chart against its own fit model, so the same hip measurement lands in different sizes - a 40-inch hip is an M at some brands and an XL at others. On top of that, some brands consistently run small or large relative to their own charts, which is why community advice like 'size up from your Knix size' exists. Our find-my-size tool reads every brand's published chart at once from one hip measurement.
- What does "12 tampons' worth" actually mean?
- Less than you'd think, and not the same thing twice. Brands count different tampons: at one brand "12 tampons' worth" means 60 mL (5 mL per tampon), at another it means 100 mL (about 8.3 mL per tampon). That 67% gap on identical words is why we normalize every claim to millilitres instead of tampon counts.
- What do the A/B/C grades on absorbency numbers mean?
- A means the brand publishes the capacity in millilitres directly - no conversion needed. B means the brand publishes tampon counts and we converted them at a stated basis. C means the brand's own sources conflict or the claim couldn't be confirmed first-party. The grade travels with the number everywhere it appears on the site.
- Are these numbers lab-tested?
- No - and we say so everywhere it matters. The site normalizes each brand's own published claims so they can be compared fairly; it is not independent measurement. Published research that tested period products with real blood has measured substantially lower effective capacity than some marketing claims. Treat the tiers as honest comparisons of claims, size up when between tiers, and plan a backup on your heaviest days.
- Is what I type into the tools private?
- Yes, by architecture: the size and absorbency math runs as code in your own browser. Your measurement and flow description are never transmitted to us, never appear in a URL, and are saved only in your own browser so the tools can work together. A one-click control clears them. There are no ad pixels or session recording on any tool page.
- Can I return period underwear if the size is wrong?
- Usually not once it's been tried on - most brands treat it as a hygiene item and offer store credit at best, sometimes nothing. That no-returns reality is exactly why we built cross-brand sizing: the first pick has to be right. The community's standing advice is to order one or two pairs to confirm fit before buying a full cycle's worth.
- How does the site make money?
- Some links to brand stores are affiliate links - if you buy after clicking, the brand may pay a commission at no extra cost to you. The data is not for sale: sizes and millilitres come from published claims, are graded the same way for every brand, and don't change based on who pays us.
Something else? Ask us directly.