Two measurements decide your underwear size, and the hip is usually the one that matters. Teen and adult underwear size charts in inches and cm, plus how each style changes the fit.
Underwear sizing is simpler than bra sizing — two measurements decide it, and the hip is usually the one that matters. What makes it confusing is that the same body can be an S in one brand and an M in another, and that letter sizes on their own tell you nothing about the actual measurement behind them. This guide gives the measurements, for teen and adult sizing, in inches and centimetres.
Underwear is cut to a waist measurement and a hip measurement. Almost every style sits on the hip rather than the natural waist, so when the two measurements point to different sizes, the hip wins.
Your natural waist is the narrowest part of your torso, usually an inch or two above the navel. An easy way to find it: bend sideways, and the crease that forms is the natural waist.
Wrap the tape around that point, keep it level, and pull it snug without compressing the skin. Breathe out normally before reading the number. Do not pull your stomach in — a measurement taken while holding your breath produces underwear that digs in all day.
Stand with your feet together. Run the tape around the fullest part of your hips and seat, which for most people is roughly seven to nine inches below the natural waist. Keep the tape parallel to the floor and check the back in a mirror, because this is where it most often rides up.
Keep the tape loose enough to lie flat against the body without pressing in. Your hip measurement is almost always the larger of the two figures, and for underwear it is the more important one.
Find the row your hip measurement falls into. The UK column is there so you can sanity-check it against the dress size you already know.
| Size | UK dress size | Waist (in) | Waist (cm) | Hip (in) | Hip (cm) |
|---|---|---|---|---|---|
| XS | 6–8 | 24–25 | 61–64 | 34–35 | 86–89 |
| S | 10 | 26–27 | 66–69 | 36–37 | 91–94 |
| M | 12–14 | 28–30 | 71–76 | 38–40 | 97–102 |
| L | 16–18 | 32–34 | 81–86 | 42–44 | 107–112 |
| XL | 20–22 | 36–38 | 91–97 | 46–48 | 117–122 |
| XXL | 24–26 | 40–42 | 102–107 | 50–52 | 127–132 |
When your waist and hip fall in different rows, follow the hip measurement.
Between two rows? Take the larger one. Underwear that is slightly loose is barely noticeable; underwear that is slightly tight rolls, digs and shows lines under clothing.
Teen underwear is sold in its own letter range, cut narrower through the hip and shorter in the rise than adult sizing at the same letter. The chart below gives the measurement behind each teen size.
| Teen size | Waist (in) | Waist (cm) | Hip (in) | Hip (cm) |
|---|---|---|---|---|
| Teen XS | 22–23 | 56–58 | 28–30 | 71–76 |
| Teen S | 24–25 | 61–64 | 31–33 | 79–84 |
| Teen M | 26–27 | 66–69 | 34–36 | 86–91 |
| Teen L | 28–29 | 71–74 | 37–39 | 94–99 |
| Teen XL | 30–31 | 76–79 | 40–41 | 102–104 |
Teen XL lines up closely with an adult XS to S in most ranges.
Teen sizing is worth re-checking every six months or so during growth. If the hip measurement has moved past the Teen XL row, adult XS or S will fit better than stretching a teen size.
Two pairs in the same size can fit very differently depending on the cut. Use this as an adjustment on top of the chart, not instead of it.
| Style | Sizing rule | Why |
|---|---|---|
| Full brief | True to size | Sits at or above the natural waist; the most forgiving style |
| Hipster | True to size | Sits on the hip bone; go by hip, not waist |
| Bikini brief | True to size | Narrower sides — size up if you are between rows |
| Boyshort | Size up if between | Cut across the thigh, so hip and thigh both matter |
| Thong | True to size | Little stretch across the back; hip measurement decides |
| Seamless / laser-cut | Size up if between | No side seam to give, so a snug row runs tight |
| High-waist | True to size | Waist and hip both need to sit in the same row |
A size label is a brand’s internal shorthand, not an industry standard. International brands cut to different national blocks, and a US M, a UK 12 and an EU 40 are not built from the same body measurements. Fabric matters as much: a cotton-elastane blend with four-way stretch will fit across a wider measurement range than a rigid lace or a laser-cut microfibre.
The practical consequence is that you should ignore the letter and read the brand’s own chart against your measurement every time you buy from a new label. Your measurement does not change; the letter attached to it does. For a closer look at how specific brands compare, see our panties size chart for women.
The hip, in almost every case. Most underwear sits on the hip rather than the natural waist, so the hip measurement is what determines whether a pair fits. High-waist styles are the exception — there, both measurements need to sit in the same row.
A 30″ (76cm) waist falls in the M row, but check your hip before deciding. If your hip measures over 40″ (102cm), an L will fit better even though the waist says M.
Age is not a reliable guide — measurement is. Most 13-year-olds fall somewhere between Teen S and Teen M, but the only way to know is to measure the waist and hip and read the teen chart above.
Multiply the inch measurement by 2.54. A 28″ waist is 71cm; a 38″ hip is 97cm. Both units are given in every chart on this page so you do not have to.
If you are between two rows, yes. Laser-cut and bonded styles have no side seam to give, so they run slightly firmer than a conventional stitched pair in the same nominal size.