Why the same word means different amounts
Every brand names its own tiers, and no standards body defines what "Heavy" has to hold in a period product. Each brand sets its ladder against its own lineup, so one brand's "Heavy" is another brand's "Moderate." The only way to compare fairly is to convert every brand's claim to a common unit, millilitres, which is exactly what the cross-brand absorbency table does, with a data-quality grade on each number.
What to do instead of trusting the label
Work from how much you actually need, not the tier word. Describe your flow in plain terms (for example, "a super tampon every two hours"), convert that to millilitres, then find the tier that covers it in each brand. A "Moderate" at one brand can out-hold a "Heavy" at another, so matching on millilitres, with margin, beats matching on the label every time.
Quick answers
- How many mL is "Heavy" period underwear?
- It depends on the brand. A tier labeled "Heavy" ranges from about 20 mL (Saalt, Proof, WUKA) to 36 to 63 mL (Knix), about a 3x spread for the same word. Compare brands in millilitres, not by the tier name.
- Is one brand's "Heavy" the same as another's?
- No. Brands set their own ladders, so one brand's "Heavy" can equal another's "Moderate." The cross-brand table normalizes every "Heavy" (and every other tier) to millilitres so you can compare like for like.
- What holds more, "Heavy" or "Overnight"?
- Usually the overnight tier holds more, but not always, and not by the same amount across brands, because both words are brand marketing, not units. Check the millilitre figure and its grade rather than assuming from the name.
Related guides
Why "12 tampons' worth" means 60 mL at one brand and up to 108 mL at another
Two brands use the same "12 tampons' worth" phrase for capacities 80% apart, and one gives no millilitre figure. The receipts, and how to compare.
How much do period underwear actually hold?
Brand claims run about 20 to 108 mL. The one lab test with real blood measured under 3 mL per pair before leaking. Both are true; here is how to use each.
What AI gets wrong about period underwear absorbency
Five failure modes: invented tampon math, marketing tags read as tiers, stale ladders, same word with a different number, claims quoted as lab facts.
Want the one-page version of the data behind these guides? The printable absorbency cheat-sheet puts every brand's tiers in millilitres on a single sheet - free, no email needed.
See what "Heavy" holds at every brand
The cross-brand table shows each brand's "Heavy" (and every tier) in millilitres, graded and dated. Or tell the translator your flow and it names the covering tier per brand.