Bikini Calculator
Estimate bikini top size, bottom size, one-piece swimwear size, cup size, and fit notes from bust, underbust, waist, hip, and torso measurements.
Estimate swimwear size from body measurements
A bikini calculator estimates bikini size by using bust, waist, hip, and underbust measurements. Measure in inches or centimeters, then compare results with a brand size chart. Bikini sizing varies by brand, fabric stretch, cup style, and coverage level.
This calculator gives separate estimates for bikini tops and bottoms because swimwear separates often fit differently. It also adds a cup estimate and a one-piece estimate when torso length matters.
Use the result as a shopping starting point, then check the specific swimwear brand's size chart, garment fabric, lining, strap adjustability, and return policy.
Estimated bikini size
--
Adjustable tops and mix-and-match separates usually give the easiest fit.
Bikini top
----
--
Bikini bottom
----
--
One-piece estimate
----
--
Cup estimate
----
--
Fit notes
Actionable notes based on your size estimate, style choice, and fit preference.
Size comparison
Approximate labels based on the calculated size. Brand charts still matter.
| Item | US letter | Approx. US numeric | Approx. EU | Best next check |
|---|---|---|---|---|
| Run the calculator to see estimates. | ||||
Fit note: This calculator estimates clothing size only. Comfort, coverage, and support depend on the exact swimsuit pattern and fabric.
How to use the bikini calculator
- Choose inches or centimeters: The calculator converts values internally and keeps the displayed unit consistent.
- Enter bust and underbust: These values estimate the bikini top and approximate bra-style cup size.
- Enter waist, high hip, and full hip: These values estimate the bikini bottom and help with high-waist or fixed-side styles.
- Add torso girth: This is useful for one-piece swimwear because torso length can change the size recommendation.
- Select style preferences: Top style, bottom coverage, and fit preference adjust the estimate toward snug, standard, or relaxed sizing.
- Compare with the brand chart: Use the result as a starting point, then check the specific garment's measurements.
How to measure for a bikini size
A bikini calculator estimates bikini size by using bust, waist, hip, and underbust measurements. Measure in inches or centimeters, then compare results with a brand size chart. Bikini sizing varies by brand, fabric stretch, cup style, and coverage level.
Use a soft tape measure, keep it level, and measure over light clothing or the undergarments you would normally use for fitting. The tape should touch the body without compressing it.
| Measurement | Where to measure | Used for | Common mistake |
|---|---|---|---|
| Full bust | Around the fullest part of the bust, level across the back. | Top letter size and cup depth. | Measuring too high or pulling the tape tight. |
| Underbust | Around the ribcage directly under the bust. | Approximate band and cup estimate. | Letting the tape slide down the back. |
| Waist | At the natural waist or high-waist bottom position. | High waist bottoms and one-piece fit. | Using low-rise position for a high-waist style. |
| High hip | Around the upper hip above the fullest seat. | Bottom rise and side strap tension. | Skipping it for fixed-waist bottoms. |
| Full hip | Around the fullest part of the hips and seat. | Bottom size and coverage choice. | Measuring with feet wide apart. |
| Torso girth | From one shoulder, through the legs, back to the same shoulder. | One-piece and long-torso fit. | Using height alone instead of the torso loop. |
Measurement reference: NIST - Body Dimensions for Apparel.
How to use the result with a real swimwear size chart
The calculator gives a starting size, but the buying decision should come from the specific brand chart. Use the result to know which sizes to compare first, then check the garment's bust, waist, hip, cup, and torso ranges.
Between two sizes
Prioritize the measurement that matters most for the garment: cup and band for underwire tops, hip for fixed bottoms, and torso for one-pieces.
Different top and bottom
Shop separates first. If a set is sold together, choose the size that fits the less adjustable piece.
Limited-stretch fabric
Woven, textured, lined, metallic, crochet, and compression fabrics usually fit less forgivingly than soft stretch nylon or spandex.
One-piece suits
Torso girth controls shoulder pull, ride-up, and lower-back gapping. Check long-torso options when the torso estimate pushes the result larger.
Apparel sizing standard reference: ASTM D5585 - Standard Tables of Body Measurements for Adult Female Misses Figure Type.
What to change if the bikini fit feels wrong
A number on a chart does not describe support, coverage, or how a swimsuit moves. Use these fit signals after trying on a bikini or comparing product photos and reviews.
| Fit signal | Likely cause | What to try |
|---|---|---|
| Top band rides up | Band is too loose or straps are doing too much work. | Try a smaller band, tighter back adjustment, or wider underband. |
| Cup spillover | Cup volume or coverage is too small for the chosen top style. | Try one top size up, fuller coverage, or bra-sized swimwear. |
| Cup gapping | Cup is too deep, straps are loose, or neckline shape is not ideal. | Try a smaller cup, adjustable straps, removable padding, or triangle style. |
| Bottom digs at the side | High hip or full hip is near the top of the size range. | Try one bottom size up, tie-side bottoms, or a higher rise. |
| Bottom feels loose in water | Fabric stretches when wet, or the dry fit was already relaxed. | Try a snugger bottom, firmer fabric, or adjustable side ties. |
| One-piece pulls at shoulders | Torso length is too short even if bust, waist, and hip fit. | Try long-torso sizing, adjustable straps, or one size up. |
Swimsuit fit reference: REI Expert Advice - Swimsuits: How to Choose.
Bikini style fit guide
Use the estimate with the style details that affect comfort most: adjustability, coverage, support, and torso length.
| Style | Best fit signal | Sizing note |
|---|---|---|
| Triangle top | Adjustable ties and cup coverage. | Often flexible, but fuller cups may need one size up. |
| Underwire top | Cup depth, band tension, and wire width. | Bra-sized options are usually more precise. |
| Tie-side bottom | Hip measurement and desired rise. | More adjustable than fixed-waist bottoms. |
| High waist bottom | Waist and high hip, not only full hip. | Size up if the waist is near the top of a range. |
| One-piece | Torso girth plus bust, waist, and hip. | Long torso fit may matter more than letter size. |
Frequently Asked Questions
What does the bikini calculator estimate?
It estimates bikini top size, bottom size, one-piece size, and approximate bra-style cup size from your measurements. It is a starting point for shopping, not a guarantee for every brand.
Why are my top and bottom sizes different?
Swimwear separates are often sized independently because bust, waist, and hip measurements do not always land in the same letter size. A different top and bottom size is common.
Should I size up or down in a bikini?
Size up when you want fuller coverage, have a long torso, are near the top of a brand's range, or the fabric has limited stretch. Size down only when the garment is adjustable and you prefer a snug fit.
How accurate is the cup estimate?
The cup estimate uses the difference between full bust and underbust. It is helpful for bra-sized swim tops, but shape, wire width, lining, padding, and brand grading still matter.
Other useful calculators
Disclaimer: This bikini calculator is for general educational and clothing-size estimation use only. It provides a mathematical starting point from user-entered bust, underbust, waist, high hip, full hip, torso girth, fit preference, top style, and bottom coverage. It is not a guarantee of fit, not a professional fitting service, not medical advice, and not a body evaluation tool. The result should not be used to judge health, attractiveness, body type, or body worth.
Swimwear sizing varies widely by brand, country, garment pattern, fabric stretch, lining, compression, cup construction, padding, underwire shape, strap placement, closure type, coverage level, rise, torso length, and intended activity. Letter sizes, numeric sizes, cup estimates, and international conversions are approximate and may not match a specific retailer's chart. A bra-style cup estimate from bust and underbust measurements is especially limited because cup fit also depends on breast shape, wire width, center gore, band tension, padding, and swim top design.
Measurements can also change the estimate if the tape is angled, pulled too tight, taken over bulky clothing, rounded differently, or entered in the wrong unit. Always compare the calculator result with the exact brand size chart, product measurements, model notes, customer reviews, fabric content, care label, return policy, and your own comfort and coverage preferences before buying or wearing swimwear.
Last updated: May 26, 2026