How to Read Underwear Sizing Charts and Get the Fit Right First Time

Quick answer

To read an underwear sizing chart accurately, measure your hips at the fullest point and your natural waist, then match those numbers to the brand's own chart rather than assuming you are the same size everywhere. Check the chart's unit (cm or inches) and whether it lists body measurements or garment measurements. When between sizes, size up for briefs and follow the bra band measurement for bras.

Underwear sizing charts are not universal. A medium in one brand can fit like a small in another, and a chart that looks straightforward can still lead you to the wrong size if you measure the wrong spot or read the wrong column. The good news is that getting it right the first time comes down to three things: knowing your actual measurements, understanding what the chart is asking for, and applying a couple of fit rules.

This guide walks you through reading any underwear size chart step by step, with specific notes for briefs, high waist styles, and bras. You will also find checkpoints to catch common mistakes before you order.

Measure your hips and waist correctly

Use a soft measuring tape and wear light clothing or nothing at all. Stand with feet together and wrap the tape around the fullest part of your hips and bottom, keeping it level all the way around. This is your hip measurement, and for most briefs it is the number that matters most. Then measure your natural waist, which is the narrowest point above your belly button, not where your jeans sit.

Write both numbers down in centimetres and inches. Most Australian brands list both, but some charts default to one unit. If you only record one, you risk comparing the wrong number to the chart. A common mistake is measuring over bulky clothing or pulling the tape tight; the tape should sit snug but not compress your skin.

• Checkpoint: the tape is parallel to the floor all the way around your hips.
• If your hip and waist measurements fall into different sizes on the chart, choose the size that matches your hip measurement for briefs.

Match your measurements to the brand's own chart

Every brand builds its fit on its own block, so always use the chart on the product page rather than a generic conversion table. Look at whether the chart lists body measurements (your body) or garment measurements (the flat-laid underwear). Body measurements are more common and easier to use. If the chart shows garment measurements, double them for a rough circumference comparison, but expect stretch fabrics to have some give.

For Sustainable Underwear Australia styles, the size options are listed per product. Start with your hip measurement for briefs and your underbust and bust for bras. If you are between two sizes, think about the fabric: seamfree styles are engineered to stretch and recover, so they can accommodate a small range, but they still have a designed fit point.

• Checkpoint: confirm the chart is in centimetres or inches before you compare.
• Do not assume your dress size equals your underwear size; they are separate systems.

Apply brief-specific fit rules

For bikini briefs, cheeky cuts, and high waist briefs, the hip measurement is the primary guide. A bikini brief sits low on the hips and should not ride or show under clothing when correctly sized. A high waist brief covers the stomach and sits higher, so the waist measurement becomes more important for comfort. If you are between sizes on a high waist style, consider sizing up if you prefer a less compressive feel.

Seamfree construction changes how a brief behaves. As the product notes explain, seamfree works like a sock: the stretch, cut, and elastic all have to work together in three dimensions. That means a seamfree brief that is too small will roll or dig, while one that is too large may lose its shape. Getting the size right is what makes seamfree feel invisible.

• Checkpoint: try the brief on and bend, sit, and walk. If it rolls down or digs in, the size or style is off.
• For high waist styles, check that the waistband stays put without folding over.

Get the bra size right with two measurements

Bra sizing needs two numbers: your underbust (band) and your bust at the fullest point. The band size comes from your underbust measurement, and the cup size is the difference between bust and underbust. Wireless bras and bra crops use the same band logic, but the cup fit is more forgiving because there is no underwire. If you are between band sizes, go with the larger band if the smaller feels tight on the loosest hook.

For D+ cup sizes, look for styles specifically engineered for that range rather than sizing up in a standard crop. A bra that is too small in the cup will cause the band to ride up at the back and straps to dig in. A bra that is too large in the band will not support properly no matter how you adjust the straps.

• Checkpoint: the band should be snug and level all the way around, and you should be able to fit two fingers under it.
• If the straps slip constantly, the band is likely too loose, not the straps.

Check the return policy before you order

Even with careful measuring, fit can vary between styles. Before you buy, read the store's returns or exchanges policy for underwear. For hygiene reasons, many retailers only accept returns on unworn items with tags attached, and some do not accept returns on briefs at all. Knowing this upfront helps you decide whether to order one size or two.

If you are unsure between two sizes, ordering both and returning the one that does not fit can be practical if the policy allows it. Otherwise, start with the size your measurements point to and adjust from there.

• Checkpoint: note the return window and any hygiene seals before removing tags.
• Keep the packaging until you have tried the item on.

Your step-by-step sizing routine

1. Measure your hips and waist: Use a soft tape over light clothing. Hips at the fullest point, waist at the narrowest point. Record in both centimetres and inches. Checkpoint: tape stays level and snug, not tight.
2. Find the brand's size chart: Open the product page and locate the chart. Confirm whether it uses body or garment measurements and which unit. Checkpoint: never use a generic conversion chart for a specific brand.
3. Match your hip measurement for briefs: For bikini, cheeky, and high waist briefs, your hip measurement is the main guide. If between sizes, size up for a more comfortable fit. Checkpoint: try the brief on and move around; it should not roll or dig.
4. Measure underbust and bust for bras: Underbust gives band size, bust minus underbust gives cup size. For D+ cups, choose a style designed for that range. Checkpoint: band sits level and snug; straps stay put without tightening.
5. Review the return policy: Check if unworn underwear can be returned and within what timeframe. Keep tags and packaging until you are sure. Checkpoint: if unsure, order two sizes only if returns are straightforward.

How specific styles fit

• High Waist Brief - Recycled Seamfree - Flame: Most seamfree briefs are just fabric cut into a shape. Ours are engineered. Seamfree works like a sock, the stretch, the cut and the elastic all have to work together in three dimensions. Get it wrong and it rolls, digs or loses its shape. Get it right and you forget you're wearing it. Our recycled rib seamfree high waist sits high with full coverage, smooth under clothing and flexible enough to stretch. Because the fit is engineered rather than just cut, choosing the correct size from the chart is what prevents rolling or digging. If you are between sizes, size up for a relaxed high waist feel.
• Recycled Wireless Bra A-D- Cranberry: Most wireless bras make a compromise between support and comfort. Ours doesn't. The elastic costs 13 times standard bra elastic. That's not a marketing line, it's why our bra still supports you properly after 100 washes when others have gone wavy and loose. The neckline doesn't dig. The underarm doesn't cut in. The straps don't slip, engineered to stay put regardless of how you move. Supportive rib knit that holds. A wireless bra relies on the band and elastic for support, so the band size from your underbust measurement is critical. If the band is correct, the neckline and underarm should not dig or cut in.
• Recycled Bra Crop D+ - Black: My daughter is a G cup. She was wearing three crops layered to get enough support for the gym. Three. So I made this. Double layer construction with fabric straps and high support elastic edge, engineered specifically for D+ bodies. The neckline sits high so nothing falls out when you bend. High support. One crop, not three. Made from GRS-certified recycled nylon from industrial waste. Oeko-Tex certified. For D+ cup sizes, a standard crop often requires layering. This style is designed for that range, so use your true band and cup measurements rather than sizing up in a regular crop.

Getting underwear sizing right the first time is mostly about measuring correctly and using the brand's own chart. Take your hip and waist measurements for briefs, your underbust and bust for bras, and apply the fit checkpoints above. If you are between sizes, size up for comfort, and always check the return policy before you commit.