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Every brand sizes and labels period underwear differently.We translate.

One hip measurement gives you your size in every brand. Tell us your flow in your own words — “a super tampon every 2 hours” works — and we show which tier in each brand actually covers it, in millilitres, with a grade for how trustworthy each number is.

Find my size in every brand What absorbency do I need?

Two questions, every brand answered

Size and absorbency are the two halves of one purchase. Answer them once and carry the results across every brand.

What size am I in this brand?

Sizing runs differently at every brand — communities trade folklore like “size up one from your Knix size.” We use the one measurement every brand publishes: your hip. Enter it once, get your size in every brand, plus how each one runs.

Find my size

Which tier actually covers my flow?

You shouldn't have to speak any brand's language. Describe your flow the way you would to a friend — how often you soak through what — and we convert it to millilitres and show the tier that covers it in each brand.

Translate my flow

“Heavy” is not the same thing twice

A tier LABELED 'Heavy' ranges from ~20 mL (Saalt, Proof, WUKA) to ~36-63 mL (Knix) across brands - roughly a 3x spread for the same word. A shopper buying 'Heavy' has no way to know which she is getting.

Brands describe absorbency in “tampons’ worth” — but they don't agree on what a tampon holds, so the same phrase can mean very different real capacity. We normalized every brand's claims onto one objective scale: millilitres. Every number is graded A, B, or C for data quality and carries the date we last verified it.

13 brands normalized44 absorbency tiers, in millilitresEvery number graded A · B · C

See the full comparison table

Private by how it's built, not by promise

Everything you enter — your measurement, your flow — is processed by code running in your own browser, on your own device. There is no account, no quiz funnel capturing your email, and no ad pixels on any tool page. We couldn't see your inputs if we wanted to: nothing is sent to us.

Read exactly how this works

Here for bladder leaks rather than periods? We keep a separate, plainly-labelled guide for leakproof underwear by absorbency.

Bladder-leak underwear

What you'll find here is each brand's own published claims, made comparable — not independent lab tests. Where a brand's numbers conflict or can't be confirmed, we say so right on the number. Read how we built the data for the conversion rules, sources, and corrections policy.