PeriodFinder

Absorbency, normalized

How much does period underwear actually hold?

Every brand measures absorbency in “tampons,” but each one defines it differently, and nobody publishes the neutral comparison. We normalized 13 brands onto one objective scale: millilitres.

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.

Updated 2026-06-11 · Every number is graded for data quality (A/B/C) · How we built this table · Our own bench test · The 2026 claims report · Printable cheat-sheet

By PeriodFinder, Editorial team

A tier labeled “Heavy” isn't the same thing twice

BrandIts “Heavy” tier holdsIn tampon-equivalentsData quality
Saalt20 mL4converted from tampon countsData quality grade B, converted from tampon counts
Proof (Proof by Always)20 mL4converted from tampon countsData quality grade B, converted from tampon counts
WUKA20 mL4brand publishes mLData quality grade A, brand publishes mL
Thinx36 mL7.2converted from tampon countsData quality grade B, converted from tampon counts
Aisle40 mL8brand publishes mLData quality grade A, brand publishes mL
The Period Company45 mL9converted from tampon countsData quality grade B, converted from tampon counts
Knix36–63 mL7.2–12.6conflicting / unconfirmed claimData quality grade C, conflicting / unconfirmed claim

Want about 40 mL of real coverage? Here's the tier you need in each brand

The same real capacity is called “Moderate” at one brand and “Super Heavy” at another. That's the gap this tool closes.

  • Knix
    Heavy(36–63 mL)Data quality grade C, conflicting / unconfirmed claim
  • Thinx
    All Day(108 mL)Data quality grade B, converted from tampon counts
  • Modibodi
    Super(50 mL)Data quality grade A, brand publishes mL
  • Saalt
    Super(40–50 mL)Data quality grade B, converted from tampon counts
  • Proof (Proof by Always)
    Overnight (Hi-Rise / Boyshort)(45 mL)Data quality grade B, converted from tampon counts
  • Ruby Love
    Period underwear (one level)(12.5 mL)Data quality grade B, converted from tampon counts
  • The Period Company
    Heavy(45 mL)Data quality grade B, converted from tampon counts
  • Bambody
    High Absorbency(10 mL)Data quality grade C, conflicting / unconfirmed claim
  • Aisle
    BOOST (adjustable, +BOOSTER insert)(20–40 mL)Data quality grade B, converted from tampon counts
  • WUKA
    Super Heavy(60 mL)Data quality grade A, brand publishes mL
  • Rael
    Reusable Boyshort(15–25 mL)Data quality grade C, conflicting / unconfirmed claim
  • Hanky Panky
    Regular(15 mL)Data quality grade B, converted from tampon counts
  • Skims
    Period Panties Brief(15 mL)Data quality grade B, converted from tampon counts

Every brand, every tier

Data quality grades: A = the brand publishes mL directly · B = converted from the brand's tampon counts · C = the brand's own sources conflict or the claim isn't first-party confirmed. Full methodology

Knix

claims verified 2026-06-11

Note: Knix's blog and live collection pages publish different super-tampon counts per tier; this table uses the live collection-page (higher) figures.

  • Light 5–15 mL Data quality grade B, converted from tampon counts
  • Moderate 18–36 mL Data quality grade C, conflicting / unconfirmed claim
  • Heavy 36–63 mL Data quality grade C, conflicting / unconfirmed claim
  • Ultra 63–99 mL Data quality grade C, conflicting / unconfirmed claim

Thinx

claims verified 2026-09-05

Note: Thinx counts a 'regular tampon' as 9 mL, so its tampon labels look smaller per-tampon than brands using ~5 mL. Normalized to mL here for honest comparison. Separately, the brand's current flagship claim is 'up to 12 regular tampons' worth' with no millilitre figure published for the period line, and it is not reconcilable with the classic tier ladder below (Super = 45 mL). The identical phrase '12 regular tampons' worth' means 60 mL at WUKA, which states 5 mL per tampon and states 60 mL, and 72 to 108 mL at Thinx, which states no figure, across the FDA regular-tampon range of 6 to 9 g (21 CFR 801.430). v3 finding (2026-06-11): the SAME 'up to 12 regular tampons' worth' claim is printed on All Day PDPs, All Night PDPs, and Teens PDPs alike - one blanket maximum across the whole period line, with no per-tier capacity ladder in current product marketing. 2026-09-05 correction: the 'up to 100 mL' on how-they-work sits in the FAQ answer about light bladder leaks and belongs to the bladder-leak line (Thinx for All Leaks), not the period line; the 2026-06-10 verification misattributed it.

  • Light (legacy ladder) 9 mL Data quality grade B, converted from tampon counts
  • Moderate (legacy ladder) 18–27 mL Data quality grade B, converted from tampon counts
  • Heavy (legacy ladder) 36 mL Data quality grade B, converted from tampon counts
  • Super (legacy ladder) 45 mL Data quality grade B, converted from tampon counts
  • All Day 108 mL Data quality grade B, converted from tampon counts
  • All Night 108 mL Data quality grade B, converted from tampon counts
  • Overnight (Teens) 108 mL Data quality grade B, converted from tampon counts

Modibodi

claims verified 2026-06-11
  • Light 20 mL Data quality grade A, brand publishes mL
  • Moderate 30 mL Data quality grade A, brand publishes mL
  • Super 50 mL Data quality grade A, brand publishes mL

Saalt

claims verified 2026-06-11
  • Light 10 mL Data quality grade B, converted from tampon counts
  • Regular 15 mL Data quality grade B, converted from tampon counts
  • Heavy 20 mL Data quality grade B, converted from tampon counts
  • Super 40–50 mL Data quality grade B, converted from tampon counts

Proof (Proof by Always)

claims verified 2026-06-10
  • Super-Light 5 mL Data quality grade B, converted from tampon counts
  • Light 5 mL Data quality grade B, converted from tampon counts
  • Moderate 15 mL Data quality grade B, converted from tampon counts
  • Heavy 20 mL Data quality grade B, converted from tampon counts
  • Super-Heavy 25 mL Data quality grade B, converted from tampon counts
  • Overnight (Super Heavy Brief) 35 mL Data quality grade B, converted from tampon counts
  • Overnight (Hi-Rise / Boyshort) 45 mL Data quality grade B, converted from tampon counts

Ruby Love

claims verified 2026-06-05
  • Period underwear (one level) 12.5 mL Data quality grade B, converted from tampon counts

The Period Company

claims verified 2026-06-11
  • Light (Thong) 10 mL Data quality grade B, converted from tampon counts
  • Medium 20 mL Data quality grade B, converted from tampon counts
  • Heavy 45 mL Data quality grade B, converted from tampon counts

Bambody

claims verified 2026-06-05
  • Leak Proof (barrier) 0–2 mL Data quality grade C, conflicting / unconfirmed claim
  • High Absorbency 10 mL Data quality grade C, conflicting / unconfirmed claim

Aisle

claims verified 2026-06-05
  • Essential Thong (Light) 5 mL Data quality grade B, converted from tampon counts
  • Essential Brief/Hipster/Boxer (Moderate) 20 mL Data quality grade A, brand publishes mL
  • BOOST (adjustable, +BOOSTER insert) 20–40 mL Data quality grade B, converted from tampon counts
  • Super (Heavy / overnight) 40 mL Data quality grade A, brand publishes mL

WUKA

claims verified 2026-06-10
  • Light 7 mL Data quality grade C, conflicting / unconfirmed claim
  • Medium 15 mL Data quality grade A, brand publishes mL
  • Heavy 20 mL Data quality grade A, brand publishes mL
  • Super Heavy 60 mL Data quality grade A, brand publishes mL

Rael

claims verified 2026-06-05

Note: Product page says 4-5 regular tampons; blog/retailer says 3.

  • Reusable Boyshort 15–25 mL Data quality grade C, conflicting / unconfirmed claim

Hanky Panky

claims verified 2026-06-11
  • Light 10 mL Data quality grade B, converted from tampon counts
  • Regular 15 mL Data quality grade B, converted from tampon counts

Skims

claims verified 2026-06-10
  • Period Panties Thong 10 mL Data quality grade B, converted from tampon counts
  • Period Panties Brief 15 mL Data quality grade B, converted from tampon counts

What these numbers are, and what they aren't

All figures are the brands' OWN maximum-capacity claims (typically saline lab tests at full saturation). The only independent test with actual blood components (DeLoughery et al., BMJ Sexual & Reproductive Health, Aug 2023, Oregon Health & Science University; 21 products tested with packed red blood cells) measured period underwear absorbing under 3 mL each (2 mL on average) before saturation - far below claimed capacity. Blood is more viscous than saline and real-world leak-free capacity is lower than lab maximums. Use this table to compare brands on a like-for-like basis; do not read any mL figure as a leak-free guarantee.

Capacity is normalized to objective millilitres (1 regular tampon ≈ 5 mL; 1 super ≈ 9 mL), because brands disagree on what a “tampon” means. Swimwear, reusable pads, removable inserts and bladder-leak lines are excluded. Figures are taken from each brand's own published claims; where a brand's own pages conflict, it's flagged above. Read the full methodology for conversion rules, sources, and the corrections policy.

Turn the table into your answer

This page is every brand's claim made comparable. The tools turn it into the tier and the size that fit you, in your browser.

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