Bikini & Swimsuit Top Size Calculator
Convert your bra size to the perfect bikini or swimsuit top. Get accurate sizing for every swimwear style, from triangle tops to underwire bikinis.
Bra Size Calculator
Advanced Mode (ABTF-style)
Use snug/tight underbust and standing/leaning/lying bust to get a recommended try-on range and style tips.
Measurement Guide
Band Size
Measure around your ribcage, just below your breasts. The tape should be snug but not tight.
Bust Size
Measure around the fullest part of your breasts, keeping the tape measure parallel to the floor.
Bra Size vs Swimwear Size
Swimwear sizing is not the same as bra sizing. Understanding the difference between cup-sized, S/M/L, and dress-size swimwear will help you find the perfect fit.
Cup-Sized Swimwear
These tops match your bra size (e.g., 34C, 36D). Best for fuller busts. Brands like Freya, Panache, and Bravissimo offer cup-sized options with underwire support.
S/M/L Sizing
Generic sizing based on band and bust range. A size medium typically fits 34-36 band, A-C cup. Less precise but more widely available in standard stores.
Dress-Size Swimwear
Some brands use dress sizes (6-20) for one-piece suits and tankinis. These consider full body measurements rather than just bust, great for matching top and bottom.
Swimwear Sizing by Style
Triangle Tops
Best for A-C cups. Sizing is adjustable via neck and back ties. For larger busts, look for padded triangle tops with wider straps.
Underwire Tops
Best for C-DD+ cups. Provides the most support and shape. Choose cup-sized underwire tops for the most accurate fit.
Halter Tops
Good for B-D cups. The neck tie provides lift and adjustability. For larger busts, look for halter tops with wider underband support.
Sport Swim Tops
Designed for active use. Compression-style with secure closures. Best for A-D cups during swimming, surfing, or beach sports.
Bandeau Tops
Best for A-B cups or as fashion pieces. Minimal support. Look for bandeaus with silicone grip strips and detachable straps for more versatility.
Water Fit Adjustment
Swimwear behaves differently when wet. Most nylon-spandex blends can stretch up to half a size when saturated, which means a snug fit when dry often becomes a perfect fit in the water.
Chlorine and salt water can also affect fabric elasticity over time. If you plan to wear your swimsuit frequently, consider a slightly firmer fit when trying on dry to account for gradual stretch.
Pro Tip: If between sizes, choose the smaller size for swimwear. It will loosen slightly when wet and you won't risk it slipping in the water.
Bikini & Swimsuit FAQ
Should I buy swimwear in my exact bra size?
Not always. While cup-sized swimwear brands match your bra size, many swimwear lines use S/M/L sizing or dress sizes. A 34C bra might translate to a medium or size 6-8 bikini top, depending on the brand and style.
Do swimsuit tops stretch out in water?
Yes, most swimwear fabrics stretch when wet. Nylon-spandex blends can stretch up to half a size larger when saturated, which is why many women prefer a snug fit when dry.
What style works best for larger busts?
Underwire bikini tops and halter necks with sturdy straps provide the best support for larger busts. Look for tops with wider side bands, adjustable straps, and built-in cups or underwire for maximum support.
How do I measure for a bikini top?
Measure your underbust (snug around your ribcage) and your bust at the fullest point, just like measuring for a bra. Use these measurements with our calculator to determine your bra size, then use the size conversion guide for swimwear.
Ready for the Beach?
Use our main bra calculator to find your exact size, then check our swimwear guide for the perfect beach look.
Go to Bra Size CalculatorOur content is researched, written, and regularly updated by our editorial team using the A Bra That Fits (ABTF) methodology — the same approach validated by the 500,000+ member r/ABraThatFits community. We cite peer-reviewed research, lingerie industry standards, and community data. Our calculators process data locally in your browser; we do not collect body measurements.
We use the modern 6-measurement ABTF method rather than the outdated +4 inch rule. This approach has been independently validated by the r/ABraThatFits community to produce more accurate and comfortable bra sizes than traditional two-measurement methods.