How do I measure for a bikini top size?

Measure snugly around your ribcage directly under your bust for the band size, then measure around the fullest part of your bust for the cup. The band size comes from the underbust measurement, and the cup comes from the difference between the two: roughly one cup letter for every 2.5 cm of difference. Keep the tape level and do not pull it tight.

How is bikini bottom size worked out?

Bikini bottoms are usually sized on your hips, measured around the fullest part. This calculator maps your hip measurement to a standard New Zealand dress size, where roughly every 5 cm of hip is one size up. If your waist and hips fall in different sizes, choose the larger of the two for a comfortable fit.

Why do bikini sizes differ between brands?

There is no single legal standard for clothing sizes, so each label cuts to its own block and target fit. A size 12 from one brand can measure differently from a size 12 from another, and imported labels often use US or European sizing. Treat the result here as a starting point and always check the specific brand's size chart before buying.

Bikini Size Calculator

This bikini size calculator turns three simple body measurements into a recommended bikini size, so you can shop online with more confidence. Enter your underbust measurement, which is the snug measurement around your ribcage just below your bust, your bust measurement around the fullest part, and your hip measurement around the widest point, all in centimetres. The calculator uses the underbust to work out your band size and the gap between bust and underbust to work out your cup, giving you a bikini top size such as 12C. It then reads your hip measurement to suggest a bikini bottom size in standard New Zealand sizing, since bottoms are cut on the hips rather than the bust. Buying swimwear online is tricky because a top and a bottom often need different sizes, and a bikini that fits your chest may be too tight or loose on the hips, so seeing both figures at once helps you avoid the returns cycle. Remember that clothing sizes are not standardised: every brand cuts to its own block, and imported labels may use US or European numbers, so use this as a sensible starting point rather than a guarantee. The defaults describe a common New Zealand size 12. Enter your own numbers, and read the worked example below to see exactly how the sizes are derived from your measurements.

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Underbust (ribcage)

Bust (fullest)

Hips (widest)

12C

recommended bikini top size (band and cup)

Bikini bottom (NZ)12

Cup sizeC

Band size (NZ)12

Sizes are a guide only. Clothing sizing is not standardised, so always check the specific brand's size chart. If your waist and hips point to different sizes, choose the larger for comfort.

How it works

The band size comes from your underbust measurement converted to inches and rounded to the nearest even number, then shifted into New Zealand sizing, where a UK 32 band is a New Zealand 12. The cup comes from the difference between your bust and your band in inches: no difference is an AA, one inch is an A, two is a B, three is a C, and so on up the scale. The bikini bottom is sized on your hips, where roughly every 5 cm steps you up one dress size around a New Zealand 12 at about 98 cm. Because both halves are derived separately, the calculator can hand you a top and a bottom in two different sizes, which is exactly why buying a matched set off the peg so often disappoints.

Worked example

Say your underbust is 81 cm, your bust is 89 cm and your hips are 98 cm. The underbust is 81 divided by 2.54, which is about 31.9 inches, rounding to a 32 band, or a New Zealand 12. The bust is about 35 inches, and 35 minus 32 is a difference of 3 inches, which is a C cup, giving a bikini top of 12C. The hips at 98 cm sit right on the size 12 mark, so the bikini bottom is a New Zealand 12. This person buys a 12C top and a size 12 bottom, a neatly matched set. Someone with the same chest but 108 cm hips would take the same 12C top with a size 16 bottom.

Related calculators

Bra Size Calculator: band and cup for everyday bras.
Waist to Hip Ratio Calculator: your waist to hip ratio.
BMI Calculator: body mass index from height and weight.
Body Fat Calculator: estimate body fat percentage.
Ideal Weight Calculator: a healthy weight range for your height.

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