How to Choose the Right Size for Women's Bikini Briefs and Brazilians

Date: 30 Mar 2026

We order online, pick the size we think is ours — and when the package arrives, the underwear either digs in or falls loose. Sound familiar? We hear it often. And it's almost never a manufacturing fault.

The most common reason is simple: underwear sizing doesn't follow the same logic as clothing sizing. In this article we'll show you exactly how to measure yourself, how to read a size chart, and how to order bikini briefs or Brazilian briefs online with confidence — and get it right the first time.

Why Underwear Sizing Is Different from Clothing Sizing

A woman who wears a size M dress doesn't necessarily wear a size M in underwear. Clothing is cut with ease allowances for movement and silhouette, and is made predominantly from woven fabrics. Underwear is cut closer to the body, but is made from elastic materials — which is why the right size is determined by body measurements, not by the label on your jeans.

At SIA Underwear we manufacture women's bikini briefs and Brazilian briefs in sizes from XS to 6XL on the European scale. All the materials we use are highly elastic — so even when measurements fall on the border between two sizes, the underwear adapts to the body and stays comfortable.

What We Need to Measure

All we need is a soft tape measure and two minutes. We measure in centimetres — the tape should lie flat against the body, neither pulling tight nor hanging loose. We recommend taking each measurement twice. The results should match.

Hip Circumference

This is the key measurement when choosing the size of bikini briefs or Brazilians. We measure at the fullest part of the hips — usually at the level of the seat. The tape is horizontal, snug but not constricting.

Waist Circumference

We measure at the narrowest point of the torso — just above the navel. This is especially important for high-waist styles, where the fit at the waist determines how comfortable the garment feels throughout the day.

How to Read the Size Chart

We find our hip measurement in the table below and select the corresponding size. If the waist falls into a different size — we go by the hips. That is the primary measurement.

Size	EU	Hips (cm)	Waist (cm)
XS	34	84–88	60–64
S	36	88–92	64–68
M	38	92–96	68–72
L	40	96–100	72–76
XL	42	100–104	76–80
XXL	44	104–110	80–86
3XL	46	110–116	86–92
4XL	48	116–122	92–98
5XL	50	122–128	98–104
6XL	52	128–134	104–110

The full SIA Underwear size chart is also available on our website.

Important: If your measurements fall on the border between two sizes — for example hips of 92 cm, which is both the upper limit of S and the lower limit of M — we recommend choosing the larger size. Underwear that digs in is not only uncomfortable but harmful to the skin when worn all day.

The Difference Between Bikini Briefs and Brazilians When Choosing a Size

For both styles the key measurement is hip circumference. The difference is in the cut, not in how we select the size.

Classic bikini briefs offer more coverage and are more forgiving of small measurement variations.

Brazilian briefs have a higher-cut back, making them ideal under fitted clothing — no visible lines, no bunching. Size selection follows the same logic: go by the hips, and when in doubt, choose the larger size.

Important for Fuller Figures

Our sizes go up to 6XL (EU 52) — hips up to 134 cm and waist up to 110 cm. The styles in our plus size lingerie category are not simply scaled-up versions of standard cuts. They are designed specifically for fuller figures — with proportions, stretch, and coverage built around real bodies.

If the difference between hips and waist is more than 20 cm, we recommend styles with a wider, softer waistband. These provide even, comfortable fit without digging in — even during a full day of wear.

In Short for the sizes

The right size in bikini briefs and Brazilians comes down to hip circumference. We measure, find our number in the chart, and when in doubt we size up. It really is that straightforward — once we know how.