Swimsuit Size Conversion

Swimwear is sized differently in every country and cut smaller than your body on purpose. Enter your bust (or your waist for men's trunks) to get the size in US, UK, Australian, EU and Italian sizing. Add your torso measurement and we will tell you whether a regular one-piece will fit, which is the part no size chart covers.

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Swimwear is the one garment people buy under the worst possible conditions: often online, often in a hurry before a trip, and with less margin for error than anything else in the wardrobe. It is also sized differently around the world, so a suit that arrives from a UK or Australian shop carries a number four sizes off what you expected. This page converts between the systems, and covers the measurement that actually decides whether a one-piece fits, which almost no size chart publishes.

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How swimwear sizing works

Women's swimsuits follow ordinary womenswear numbering, anchored to the bust: a US 8 fits about a 36 inch bust, and the same suit is a UK 12, an Australian 12, an EU 40 and an Italian 46. Men's trunks follow waist inches and letter sizes, the same ladder as shorts. That much is simple arithmetic, and the tool above does it.

What makes swimwear different is not the numbers. It is that swimwear is deliberately cut smaller than your body.

Negative ease, and why swimwear feels tight in the shop

Most clothes are cut larger than the body they fit, so you have room to move. Swimwear does the opposite: it is cut with negative ease, measuring less than you do and stretching to meet you. That is not a manufacturing meanness, it is the only way a suit stays put in water. Wet fabric relaxes, and a suit that felt comfortable dry will sag once it is swum in.

So the fitting-room rule for swimwear inverts. It should feel snug, close to the point of being slightly too tight, because it will give about half a size in water. If it feels comfortable and relaxed on the hanger side of dry, it is probably a size too big. Our body vs garment measurements page covers ease generally; swimwear is its most extreme everyday case.

The measurement nobody publishes: torso length

For a one-piece, bust is not the number that decides fit. Torso length is. Measure from the top of your shoulder, down the front through the crotch, and back up to the same shoulder point. That loop is your torso measurement, and it typically runs about 60 to 65 inches for a woman wearing a US 4 to 10.

If yours is longer than the range for your size, a regular one-piece will pull down at the shoulders and ride up at the leg no matter how well the bust fits, and it will do that in every brand, which is why long-torsoed people often conclude that one-pieces just do not suit them. The usual response, sizing the whole suit up, is the wrong fix: it buys a loose bust and only a little extra length. The right fix is a suit cut for a long torso, which many brands sell as a separate length option, or a two piece, where torso length stops mattering entirely. Enter your torso above and the tool flags this for you.

Worked example

Your bust measures 36 inches, so you are a US 8 swimsuit: a UK 12, an Australian 12, an EU 40, an Italian 46, letter size M. Now the part that matters for a one-piece. Your torso measures 67 inches, and the typical regular-fit range for a US 8 is 62 to 65. You are 2 inches over, so a regular one-piece will fight you at the shoulders regardless of the bust being right. Buy the long torso version of the US 8, not a US 10.

Women's swimsuit conversion chart

Bust is the size each row is cut for. Torso is the typical regular-fit range, which brands vary, so treat it as the flag for a long torso rather than a precise threshold.

USUK / AUEUITLetterBustTypical torso
043238XS32 in58 to 61 in
263440XS33 in59 to 62 in
483642S34 in60 to 63 in
6103844S35 in61 to 64 in
8124046M36 in62 to 65 in
10144248M37.5 in63 to 66 in
12164450L39 in64 to 67 in
14184652L40.5 in65 to 68 in
16204854XL42 in66 to 69 in
18225056XL44 in67 to 70 in
20245258XXL46 in68 to 71 in

Men's swim trunks

Trunks follow the shorts ladder: waist inches into letter sizes, with a drawstring that forgives an inch either way, which is why men's swim sizing feels more relaxed than trouser sizing.

LetterWaistWaist sizeEU (approx)
XS26 to 27 in26 to 2742 to 43
S28 to 30 in28 to 3044 to 46
M32 to 34 in32 to 3448 to 50
L36 to 38 in36 to 3852 to 54
XL40 to 42 in40 to 4256 to 58
XXL44 to 46 in44 to 4660 to 62
3XL48 to 50 in48 to 5064 to 66

Two pieces, and competition suits

A two piece is the honest answer for anyone whose top and bottom disagree, which is most people. Bought as separates you can take a different size in each, and bikini tops are increasingly sold in real bra sizes rather than S, M and L, which is a genuine improvement: if a top gives a band and cup, use your bra size rather than guessing a letter. Bottoms follow the hip measurement, so if your hip is a size above your bust, buy for the hip.

One warning about competitive swimwear. Racing suits from brands like Speedo and Arena are cut far smaller than fashion swimwear, sometimes two or three sizes down, because they are designed to compress. A person who wears a US 8 in a fashion one-piece may need a US 12 equivalent in a racing suit, and the brand's own chart is the only reliable guide. Do not carry a fashion size across to a competition suit, and do not carry a competition size back the other way.

Frequently asked questions

What is a US swimsuit size in UK sizing?

Add four. A US 8 swimsuit is a UK 12, a US 12 is a UK 16, and a US 4 is a UK 8. Australian sizing follows the UK numbers, so a US 8 is also an Australian 12. For Europe add 32 to the US size, and for Italy add 38, so that same US 8 is an EU 40 and an Italian 46.

Why does swimwear feel so tight when it fits?

Because it is cut with negative ease, meaning the garment measures less than your body and stretches to meet it. A suit that fits loosely while dry will sag once it is wet, since the fabric relaxes in water. Buy swimwear snug, close to slightly too tight, and expect it to give about half a size in the water.

How do I measure my torso for a one-piece?

Start at the top of your shoulder, run the tape down the front of your body, through the crotch, and back up to the same point on your shoulder. That loop is your torso length, and it typically runs about 60 to 65 inches for a woman wearing a US 4 to 10. It is the measurement that decides whether a one-piece fits.

Why does my one-piece pull down at the shoulders?

Almost always because your torso is longer than the suit was cut for, not because the size is wrong. A long torso in a regular one-piece drags the straps down and rides up at the leg however well the bust fits. Sizing up the whole suit is the common mistake, since it mostly buys a loose bust. Look for a long torso version, or wear a two piece, where torso length does not apply.

What size swim trunks do I need for a 34 inch waist?

A men's medium, since the M band covers roughly 32 to 34 inches, which is a waist size 34 and about an EU 50. Trunks usually have a drawstring, so they forgive an inch either way, which is why men's swim sizing feels less exact than trousers.

Should I buy a bikini top by bra size or by S, M and L?

By bra size whenever the brand offers it. A top sold with a band and cup, like 34C, will fit far more predictably than one sold as a medium, because a letter has to cover several cup volumes at once. If only letters are offered, use your bust measurement and expect more variation. Buying separates also lets you take a different size top and bottom, which suits most people.

Do competition swimsuits use the same sizes?

No, and this catches people out. Racing suits from brands like Speedo and Arena are cut to compress, so they run two to three sizes smaller than fashion swimwear. Someone who wears a US 8 one-piece for the beach may need the equivalent of a US 12 in a racing suit. Use the brand's own chart and never carry a fashion size across.

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