The most common sizing question with bikinis isn't about fit in a general sense — it's that tops and bottoms don't always match in the same size. You might need a medium top and a large bottom, or the reverse. That's completely normal, and buying separates handles it cleanly.
For tops, size determines how much cup surface area you get. Triangle tops with adjustable ties are the most forgiving because the string lets you compensate in both directions. If you're between sizes, go up for more coverage, go down for a snugger and more supported fit. Strapless styles have less adjustment range, so follow the measurement chart more closely for those.
For bottoms, measure your hips, not your waist. Brazilian cut bottoms sit lower on the hip, so the hip measurement is what actually determines fit. Between sizes: sizing up gives you more comfortable back coverage, sizing down gives you the more minimal Brazilian look.
Our size guide has exact measurements for each style. The model in our photos wears Medium and is 5'7" — that's a useful reference if you're deciding between two sizes. If you're taller or have more hip-to-waist contrast, sizing up usually works better.
If you're genuinely uncertain, sizing up is the lower-risk call. We accept exchanges within 30 days on unworn pieces with the hygiene liner intact. We'd rather you get the fit right than keep something that doesn't feel good.