The two measurements that matter
Everything in panty sizing starts with the natural waist, measured at the narrowest point of the torso usually just above the navel, and the fullest point of the hip, measured across the seat with the tape level. Both are taken against the skin or over thin knitwear, standing upright, with the tape snug but not compressing. Unlike bra sizing there is no subtraction step: the two readings map directly onto a letter or a number.
The hip carries more weight in the fit than the waist does for most wearers, because the waistband is elastic and the leg openings are cut-in edges. A brief that matches at the hip but misses at the waist rolls; one that matches at the waist but misses at the hip either cuts in at the leg or slides up through the day. Consumer guides often lead with the waist because it is easier to find, but grading engineers place the hip girth first in the size table.
Letter sizes, numeric sizes and the mapping
Letter grids from XS to 3XL dominate the category, with numeric labels from 5 to 13 common in US retail as an alternative on the same garments. The mapping between them is broadly consistent, with plants shifting boundaries by one size in either direction:
| Letter | US numeric | Natural waist (in) | Full hip (in) |
|---|---|---|---|
| XS | 5 | 24-25 | 34-35 |
| S | 6 | 26-27 | 36-37 |
| M | 7 | 28-29 | 38-39 |
| L | 8 | 30-31 | 40-41 |
| XL | 9 | 32-33 | 42-43 |
| 2XL | 10 | 34-35 | 44-45 |
| 3XL | 11 | 36-37 | 46-47 |
Both labels describe the same body; the letter grid is what most multi-packs and marketplace listings publish, while the numeric grid appears where brands want finer steps without adding letters. Period panties typically publish XS-3XL with the same body mapping and a structure note, since the absorbent layers add thickness through the seat; the period line keeps the same letter grid as the rest of the category for exactly that reason.
Regional overlays follow the same body measurements through different scales. European charts publish hip-weighted numbers in the 36-46 range, UK charts run 8-20, and the letter grid maps onto both without changing the underlying grade rule. For an export program this is a labeling exercise rather than a fitting exercise, provided the master grid is written as body measurements and the local labels are derived from it. The mistake to avoid is inheriting a regional chart and grading from it directly, which bakes someone else's boundary choices into your patterns.
Measurement errors in this category mirror the bra ones with one addition: time of day. Waist readings drift through the day as people eat and drink, and hip readings change with posture, so consumer guides advise a morning measurement while production grading assumes a standardized neutral posture on the fit form. The two never match exactly, which is one more reason tolerance windows belong in the spec sheet rather than single-point numbers.
Rise and leg opening: where inseam thinking applies
A panty has no inseam in the trouser sense - there is no leg to measure down - but the logic that the inseam serves in trousers carries over as geometry below the waist. Three dimensions decide how a style sits: the rise (how far below the natural waist the front and back panels start), the side width at the hip, and the leg opening circumference. The common styles place those dimensions in a narrow, learnable band:
| Style | Side and rise geometry | Coverage note |
|---|---|---|
| Brief | High, mid or low rise; full side | Full seat coverage |
| Bikini | Low rise; side typically 5-8 cm | Seat coverage, higher leg line |
| Boyshorts | Mid rise; short leg like a boxer | Full leg and seat coverage |
| Thong | Low rise; minimal side | T-shaped rear panel |
The same hip measurement produces different pressure at the leg edge across these styles. A boyshorts leg opening sits low on the thigh like a short inseam and must not bind; a bikini side sits high on the hip and must not roll. That is why the panty styles guide treats coverage and rise as separate decisions from size: a wearer can be an M in every style and still prefer a different rise per outfit. The style choice note walks that decision for consumers.
Stretch tolerance and what it hides
Knit underwear stretches, and the stretch is doing real work: a grid with 2 to 4 inches of waist tolerance can hold a wearer across two letter sizes. But stretch hides grading debt. A narrow grade rule on a high-elastane knit can pass a fit check at the middle size and fail at 3XL, where the waistband elastic reaches its working extension and starts to roll or dig. Fabric weight, elastane percentage and the elastic construction in the waistband all move the effective range of one size; the waistband types are laid out in the elastic note.
Planning sizes for production
Panty programs are planned as ratios. Multi-packs and marketplace bundles need a size mix per carton, and plants quote minimums per color across the size run - typically 2,000-5,000 pieces per color for branded programs, with the ratio inside the lot confirmed in writing per order. Reference minimums and sampling timelines are on MOQ and lead time.
Three decisions shape the run. First, depth: a core XS-2XL grid covers most demand, and extending to 3XL opens the plus segment without changing the construction of most styles. Second, the fit block: brief and boyshorts share more of their grade rule than either shares with a thong, so style families are graded as blocks to keep the SKU count low. Third, documentation: the declared chart, the grade rule and the tolerance per measurement point go into the spec sheet, and inspection checks production against it. A program brief with the size ratio fits the quote form directly, and the brief line page shows how a single style publishes its grid.