How to choose a swimsuit online without ordering three sizes

A swimsuit is the hardest garment to buy online. Two pieces with the same label can sit differently at the bust, cut differently at the leg, and behave nothing alike in water. The fix is not to order three sizes and return two. It is to know the four numbers that matter, read the fabric, and preview the cut on your own photo before you check out.

Measure once, in the right place

You need four numbers: bust, underbust, waist and hip.

• Bust: around the fullest point, tape level, arms down.
• Underbust: snug around the ribcage, exhaled.
• Waist: the narrowest point, usually above the navel.
• Hip: the widest point, usually 18-22cm below the waist.

Write them down in centimetres. Brand charts are inconsistent, but your numbers are not. Our size guide turns them into a starting size and shows a confidence band so you know how much to trust it.

Read the fabric before the size

The same size behaves differently at 6% elastane and 22% elastane.

• Low stretch (under 10%): unforgiving at the waist and leg. Size up if you are between sizes.
• Mid stretch (10-18%): most one-pieces and bikinis. True to chart.
• High stretch (over 18%): forgiving, but can thin out and lose opacity when wet.

If the product page does not list composition, treat the fit as unknown and check reviews for "runs small" language.

Decide coverage by activity, not by trend

A high-cut leg is a style choice. A high-cut leg on a swimsuit you plan to swim laps in is a fit problem. Decide what the suit has to do first:

• Lap swimming: higher neckline, fixed straps, moderate leg, chlorine-resistant fabric.
• Beach and pool days: adjustable ties, removable cups, higher leg is fine.
• Resort and cover-ups: fit matters less than how the piece layers.

Preview the cut on your own photo

Product photos are shot on one body, in one pose, under one light. A visual preview is a better question than "will this look good on me": it shows where the neckline lands, how high the leg sits, and whether the print reads the way you expected.

Upload one full-length photo to the AI swimsuit changer, pick a one-piece, a bikini or a cover-up, and compare four candidates. Keep your own pose for the most honest comparison. The preview does not simulate fabric physics, so still check the chart for size.

The three-question checklist

Before you buy:

1. Does the bust construction match your support needs? Soft cups, underwire and compression linings are not interchangeable.
2. Is the leg line compatible with what you will do in it? High cut and lap swimming fight each other.
3. Does the fabric match the water? Chlorine destroys elastane; salt and sun fade cheap prints.

A preview answers the visual question quickly. Measurements and fabric answer the fit question. You need both, and you need them before the return window starts.