Bra sizing and underwear sizing run on completely different systems. Your bra band and cup number tells you almost nothing about your panty size. Enter your hip measurement below to get your actual size.
Why Underwear Sizing Works Differently
Bras size around your ribcage (band) and bust (cup). Underwear sizes almost entirely around your hip measurement, sometimes combined with waist.
That’s why someone can be a small band/large cup on top and a completely average size on the bottom. The two systems aren’t related, and shopping for one doesn’t tell you anything reliable about the other.
How To Measure Correctly
Measure around the fullest part of your hips and rear, keeping the tape level and snug but not compressing skin. Most sizing mistakes come from measuring too high (at the waist) or letting the tape sag in the back.
Letter vs. Numeric Sizing
US brands mix letter sizing (XS-3X) and numeric sizing (0-20) inconsistently. This tool gives you both, plus UK and EU equivalents, so you’re covered no matter which system a specific retailer uses.
Why Hip Measurement, Not Waist
Underwear sizing is based on hip measurement rather than waist because the hip is the widest, most consistent point most styles need to fit around comfortably. Waist measurement varies more by where exactly you measure and doesn’t predict fit as reliably across different cuts.
A Note on Style Differences
The same labeled size can fit differently depending on the cut. A high-waist brief and a low-rise thong in the same size use different amounts of fabric and different stretch zones, so a size that’s perfect in one style can feel slightly different in another from the same brand. Use this calculator’s result as your reliable starting size, then adjust slightly for specific styles as needed.
One Measurement Usually Is Enough
Unlike bra sizing, which needs two measurements to capture both band and cup, panty sizing typically only needs your hip measurement. One number, one lookup, done.
Why Panty Sizing Only Needs One Measurement
Unlike bra sizing, which needs both underbust and bust to capture two independent dimensions (band and cup), panty sizing is driven almost entirely by hip circumference. That’s why this tool asks for just one number instead of two. It genuinely is a simpler measurement to get right.
How the Size Table Was Built
The table behind this calculator uses standard published hip-measurement ranges (34 inches and up through 48-plus, mapped to XS through 3X) cross-referenced with common US numeric, UK, and EU equivalents. These are the widely used industry ranges, not a proprietary scale, so the results should track reasonably closely with most mainstream retailers.
Why Panty Sizing Still Varies More Than You’d Expect
Even with one simpler measurement, cut matters enormously. A high-waisted brief and a low-rise bikini cut in the same labeled size can fit completely differently at the waist and leg opening, even though hip circumference is identical. Stretch fabric content also varies a lot between styles, which affects how forgiving a given size actually is in practice.
What to Do If You’re Between Two Sizes
For most styles, sizing up is the safer default when you’re right on the boundary. A slightly loose fit in stretch fabric is more comfortable to live with than one that’s genuinely too tight, especially in less-stretchy styles like certain briefs or shapewear-adjacent cuts.
A Note on Fabric Stretch
A size that feels perfect in a cotton brief can feel different in a lace or satin style with less give. If you regularly wear a mix of fabrics, it’s worth checking fit separately rather than assuming one size works identically across every material.
If you regularly buy from the same brand, keeping a note of which specific size worked well there saves time on future orders.
One More Reason Hip Measurement Alone Works
Unlike bras, which need two measurements to separate band support from cup volume, underwear generally doesn’t have that same two-part structural distinction, which is why a single hip measurement captures what matters most for fit.