Swimwear Size Guide: How to Measure for Men's & Women's Swim

To find your correct swimwear size, measure your bust or chest, waist and hip with a soft tape measure, then compare those numbers against the specific brand's own size chart rather than your usual clothing size. Women should also measure band and bust separately for any style with cup sizing. Because there is no single mandatory sizing standard in Australia, this step matters more with swimwear than almost any other garment.

Few things are more frustrating than ordering swimwear online, waiting for it to arrive, and finding it either gapes at the leg or digs in at the bust. Swimwear tends to fit less forgivingly than everyday clothing, and sizing varies more between brands than most people expect. This guide walks through exactly how to measure yourself for both men's and women's swimwear, how to read a size chart properly, and why relying on your normal clothing size so often goes wrong.

Why Swimwear Sizing Varies So Much Between Brands

It might seem odd that a size 12 in one swimwear brand can fit completely differently to a size 12 in another, but there is a straightforward reason. Australia once had a formal sizing standard for women's clothing, AS 1344, which set out standard body measurements linked to each size number. That standard was withdrawn in 2017 and has not been replaced, meaning there is currently no mandatory, uniform sizing system that Australian clothing and swimwear brands are required to follow. Each brand is free to set its own size chart based on its own fit model and target customer, which is the single biggest reason two garments labelled the same size can fit so differently.

This is exactly why measuring yourself and checking the specific product's own size chart, every single time, is a more reliable method than assuming a size will carry across from one brand to the next, or even from one style to another within the same brand.

What You Need to Measure Yourself Properly

You only need two things: a flexible, soft tape measure of the kind used for sewing, and a mirror if you are measuring yourself alone. A rigid tape measure or ruler will not sit properly against the curves of the body and will give an inaccurate result.

When measuring, keep the tape snug against your skin without pulling it tight enough to compress the area, and keep it level and parallel to the floor all the way around your body rather than angled up or down at the back. Measuring over light clothing rather than directly on skin is fine, but avoid measuring over anything bulky.

How to Measure Yourself for Women's Swimwear

Follow these steps in order for the most accurate result.

• Measure your bust. Wrap the tape measure around the fullest part of your bust, keeping it level across your back. Do this without a padded bra for the most accurate reading.

• Measure your band. Wrap the tape measure snugly around your ribcage, directly under your bust, keeping it horizontal all the way around.

• Work out your cup size. Subtract your band measurement from your bust measurement. Each inch of difference corresponds to one cup letter: a 1 inch difference is an A cup, 2 inches is a B cup, 3 inches is a C cup, 4 inches is a D cup, and so on. If you are measuring in centimetres, convert to inches first, since cup sizing is based on inch increments even in countries that otherwise use metric measurements.

• Measure your waist. Find your natural waistline, generally the narrowest point above your belly button, and wrap the tape around it without pulling it tight.

• Measure your hips. Stand with your feet together and measure around the fullest part of your hips and bottom, keeping the tape level.

Once you have these four numbers, bust, band, waist and hip, you can compare them against almost any brand's size chart, including styles with separate cup sizing such as underwire bikini tops or structured one pieces.

How to Measure Yourself for Men's Swimwear

Men's swimwear sizing is generally simpler, since most styles rely on a single waist measurement rather than a combination of band and cup sizing.

• Measure your waist. Find your natural waistline, roughly level with your belly button, and wrap the tape measure around it without pulling it tight. This is the primary measurement used for briefs, trunks and jockstraps.

• Measure your hips. For fuller cut styles such as boardshorts, measure around the fullest part of your hips and seat as well as your waist, since the two can be listed separately on some size charts.

• Measure your inseam if length matters. For boardshorts and swim trunks with a specific length listed, measure from the crotch seam of a well fitting pair of shorts down to where you want the hem to sit, rather than guessing based on height alone.

If you are also deciding between cuts such as briefs, trunks or jockstraps rather than just sizing, our men's swimwear style guide covers how each style fits differently once you have your measurements.

Reading a Swimwear Size Chart

Once you have your measurements, compare them directly against the specific product's size chart rather than a general size guide for the brand as a whole, since swimwear ranges are sometimes sized differently to the rest of a label's clothing. Most charts list a range of centimetres or inches for each size letter or number, so look for the size where all of your relevant measurements, not just one, fall within range. If your measurements sit across two different sizes, most swimwear brands recommend sizing up rather than down, particularly for structured or underwire styles, since a snug fit that gapes in one spot is harder to fix than a slightly looser one.

For a wider look at how sizing works across underwear, lingerie and swimwear generally, our full guide on how underwear and swimwear sizing works is worth reading alongside this one.

Fabric and Fit Work Together

The fabric a swimsuit is made from affects how forgiving its sizing actually is. A style with a high spandex or elastane content will have more give than one built from firmer, chlorine resistant polyester or PBT blends, so a suit sitting right on the edge between two sizes may behave differently depending on what it is made from. Our swimwear fabric guide explains how different fabrics stretch and recover, which is useful context once you already know your measurements.

Fit also matters more than usual for styles with extra structure or support, such as those covered in our plus size swimwear guide, since band and cup accuracy has a bigger impact on comfort in fuller support styles than in a simple soft cup bikini top.

A Note on International Size Conversions

Shopping from an overseas swimwear brand adds another layer of inconsistency on top of the usual brand to brand variation. As a general rule, Australian sizing tends to sit closer to UK sizing, while US sizing often runs smaller under the same size number for a similar body measurement, and European sizing typically uses a completely different numbering system again. These are broad patterns rather than fixed rules, and they can vary from brand to brand even within the same country, so the safest approach is always to compare your actual centimetre or inch measurements against the specific brand's chart rather than assuming a size 12 in Australia converts neatly to a specific number elsewhere.

Testing the Fit Once It Arrives

A size chart gets you close, but a few simple checks once you try a piece on will confirm whether it actually fits. Raise both arms above your head and move them in a full circle, since a bikini top or one piece that shifts, gapes or rides up during this movement will do the same thing in the water. Do a full squat and stand back up, which is the fastest way to reveal whether bottoms are going to ride up or gape at the leg during normal movement rather than just while standing still. For structured or underwire styles, check that the band sits horizontally all the way around without riding up at the back, and that the underwire sits against your ribcage rather than digging into breast tissue. If a piece fails any of these checks, it is worth sizing up or down before committing to it as your regular swimwear size with that brand.

Common Measuring Mistakes to Avoid

• Measuring over a padded or push up bra, which inflates the bust measurement and throws off cup sizing

• Pulling the tape measure too tight, which results in a size that runs small once you try the garment on

• Relying on your usual clothing or bra size instead of measuring specifically for the swimwear brand and style you are buying

• Skipping the waist or hip measurement for styles where only one number is listed on the product page, then being surprised when the fit is uneven

• Assuming your size will stay identical across every style from the same brand, when cut and fabric can shift sizing style to style

Quick FAQ

Why do I need to measure for swimwear separately from my regular clothing size?

Swimwear fits closer to the body than most clothing and stretches differently, and Australia has no mandatory sizing standard that brands are required to follow, so numbered and lettered sizes vary significantly between labels. Measuring yourself and checking the specific chart is more reliable than relying on your usual size.

What if my measurements fall between two sizes?

Most brands recommend sizing up rather than down, particularly for structured, underwire or firmer fabric styles, since a suit that is slightly loose is generally more comfortable and easier to adjust than one that is genuinely too small.

Do I need to measure differently for a bikini top with underwire?

Yes. Underwire and structured bikini tops use band and cup sizing in the same way as a bra, so you need both your band measurement and your bust measurement to work out the correct size, rather than a single generic small, medium or large.

How often should I re-measure myself for swimwear?

It is worth re-measuring at least once a year, or after any significant change in weight, fitness routine or, for women, after pregnancy or breastfeeding, since band and bust measurements in particular can shift noticeably over time.

Should I choose a lettered size or a numbered size if a brand offers both?

Where a brand offers both, use whichever system its own size chart maps most precisely to your measurements rather than picking based on habit. Some brands convert lettered sizes such as small or medium using wider measurement ranges than their numbered equivalents, so the numbered size can occasionally give a more precise fit if your measurements sit near the edge of a lettered range.

Taking five minutes to measure yourself properly before you buy is the single most effective way to avoid an ill fitting swimsuit, regardless of which brand or style you choose. For the full picture on swimwear styles and fabric, head back to our complete swimwear style guide, or go ahead and shop swimwear now that you know your measurements.