Swimsuit Size Chart and Support Picker

A swimsuit that looks perfect on the hanger can still slip at the straps or pinch at the hips. Start with your underbust, fullest bust, and hip measurements, then use the swimsuit size calculator below for a starting point. Check the result against the brand’s own chart before buying.

For bikini separates, fit the top to your band and bust and the bottom to your hips. For a one-piece, check bust, waist, hips, and torso length together. Then choose the support you need, from a soft triangle for lounging to a secure racerback for swimming. The calculator offers guidance, not a universal brand size.

How the Swimsuit Size Chart and Support Picker works

Your inputs, bra size, underbust, hips, tummy control

• Bra size and underbust shape cup volume and band tension.
• Hips drive bottom size and one piece ease.
• Tummy control preference selects lining strength, none, light, firm.

What I learned: Cup volume without band tension felt wobbly in water. Now I weigh both.

What you get, size, style, support score

• Sizes: Separate top and bottom, plus one piece.
• Style pick: Triangle, balconette, longline, halter, racerback, one piece, high waist bottom.
• Support score: 0 to 100. Under 30 lounge. 31 to 60 all day swim. 61 to 100 active hold.

Measure once, convert cleanly

Underbust and bust for cup volume

• Tape under the bust, snug and level. Write underbust in inches.
• Tape over the fullest bust point without squashing. Write bust in inches.
• Cup difference guide: Some US fitting methods use roughly 1 inch per cup step, but cup letters depend on the band-size method and brand. Do not assign a cup letter from bust minus raw underbust alone; use the brand’s bra-sizing instructions or a well-fitting bra as your starting point.

Tiny miss: I measured in a sports bra and lost an inch. Now I use a thin, unpadded bra or no bra.

Hips for bottoms and one piece

• Feet together.
• Tape around the fullest hip and seat.
• Use that number to compare bikini bottoms with the brand’s hip chart. For one-pieces, hip size alone is not enough; bust, waist, and torso length matter too.

Check torso length for one-piece swimsuits

For a one-piece, measure a loop from the top of one shoulder, down the front and between your legs, then up your back to the same shoulder. Keep the tape comfortably close to your body. Compare the result with the brand’s torso or girth chart, especially if one-pieces tend to pull at your shoulders or sag through the middle.

Sister sizes for swim tops, plus a worked example

If a bra-sized swim top has cups that fit but its band is too tight or too loose, a sister size may help. This does not apply to every S/M/L swim top.

• Down band, up cup, 34D → 32DD.
• Up band, down cup, 34D → 36C.
  Use this for tops only. Keep bottoms true to hips.

Worked example: Suppose you measure 33 inches under the bust, 37 inches around the bust, and 41 inches at the hips. Enter those measurements in the calculator, then compare the suggested sizes with the brand chart. A 41-inch hip may be a medium in one line and a large in another. If you already wear a well-fitting 34D and the swim top’s band is loose, try a 32DD in the same bra-sized style, provided the cup and band both feel right.

If you shop across regions, use a swimsuit sizes conversion chart or our International Size Converter before you compare brand charts. If you prefer a guided flow, our step by step works like a simple swimsuit size calculator.

Style guide by goal

Lift, balconette and longline

Why it helps: Underwire and a wider band spread weight, so straps stop digging once you are wet.
What to try: Start at your true bra size. If the back floats, drop the band and raise the cup, 34D to 32DD.
Quick check: Underwire, wider straps, back clasp, optional longline.

My miss: I chose narrow straps and they cut in by noon. Wider straps fixed it without changing size.

Lounge, triangle and bralette

Why it helps: Soft cups and easy ties for sun and short dips.
What to try: Fit the underbust first. If cups float, tighten the tie before moving up a size.
Quick check: Adjustable ties, removable cups, double layer fabric.

Note: I once sized up for coverage and got side gaping. I stayed in the same size and picked a triangle with more side fabric instead.

Laps, racerback and cross back

Why swimmers like it: Straps cross or lock and pull weight to your back, not your neck.
Set it up: Stay true to band. For D and up, choose a higher center front so things stay put on turns.
Quick check: Cross back straps, firm elastic at the ribs.

Pool day: I kept yanking a halter between laps. Cross back and I forgot about it.

Smoothing, one piece and high waist bottom

Why it helps: Power mesh panels smooth without strangling your midsection.
What to try: Compare your bust, waist, hips, and torso with the size chart. Choose light or firm shaping based on comfort and the garment’s construction.
Quick check: Lined front, medium or high leg opening so the suit does not cut in.

Lesson learned: I sized up for tummy control and lost hold at the bust. Back to true hip size with firm mesh looked cleaner and stayed put.

The support score, in plain English

Think of this as a simple comparison of support features, not a scientific rating. A secure band, supportive cups, stable straps, coverage, and lining can all contribute to a more secure feel. Fit still matters more than the total.

• Band: pull on 5, clasp 10, longline 15
• Cups: unlined 5, lined 10, molded or underwire 20
• Straps: spaghetti 5, standard adjustable 10, cross back 15
• Center: plunge 5, mid 10, high 15
• Fabric: single 5, double 10, power mesh 15

For illustration, adding the listed feature points gives 80 for a longline band, underwire cups, cross-back straps, high center, and power mesh. A pull-on band, unlined cups, thin straps, plunge center, and single fabric total 25. These are editorial feature scores, not laboratory measurements or guarantees of fit. The embedded calculator may use its own scoring rules.

Worried a balconette feels stiff, pick unlined underwire for a lighter feel.

Mix and match rules that save returns

• Top follows underbust and cup.
• Bottom follows hips.
• One piece needs bust, waist, hips, and torso length; compare all four with the brand chart.
• Between sizes, follow the brand’s guidance and check where the suit feels tight or loose. Use sister sizing only for bra-sized tops.
• Halter loads the neck. Cross back spreads the work.

Fit notes for special cases

• Long torso: Prioritize torso length in one pieces or pick a two piece.
• Nursing: Cross front styles or clips help without changing size.
• Post surgery: Look for pockets for inserts, higher centers, and soft linings.
• Plus sizes: Secure the band first, then adjust cup with sister sizes. Avoid upsizing bottoms if hips already fit.

Who this is for, How I tested this, Why it works

• Who this is for: Anyone who wants a suit that stays put in real water, not just a mirror.
• Fit checks worth doing: Try a few arm raises, a forward bend, and a gentle squat. Watch for slipping straps, a rising back band, rolling waistbands, or uncomfortable pressure. Repeat the checks when the suit is wet, if possible.
• Why it works: Band fit and cup coverage affect top stability. Hip measurements help with bottoms, while one-piece comfort also depends on torso length. Mesh and strap design may improve the feeling of security, but the score is a rough guide rather than a validated measure of support.

Fit insurance: If a retailer offers free returns on unworn swimwear, comparing two top sizes can be helpful. Check hygiene-liner and return-policy requirements before ordering.

Key takeaways

• Start with underbust, bust, and hips, not guesswork.
• Use the brand’s swimsuit size chart. Consider sister sizes only for bra-sized tops.
• Pick style for your day, lift, lounge, laps, smoothing.
• Choose light or firm shaping based on comfort; do not assume a tighter or larger suit automatically fits better.
• Cross back spreads load better than a halter on long days.

FAQs

More sizing tools

• Bra Size and Sister Size Finder, confirm your band and cup before picking a swim top
• Balconette vs Plunge, see shapes and coverage at a glance
• International Size Converter, quick US, UK, EU mapping for brand charts
• Shoe Size Converter with Fit Notes, keep the sizing momentum going
• Tools hub, browse all calculators and fit tools
• Ring Size Finder and Calculator, measure at home and convert to US and UK
• Jeans Fit Calculator, find your waist, rise, and inseam
• Cost Per Wear Calculator, buy fewer pieces that earn their keep
• Size up or down, solved. Use the finder
• Skip returns, confirm your size now, Hat Size Calculator