The honest starting point is that you cannot judge a dress from a product photograph, so stop trying. What you can judge is the specification, and designer listings carry more of it than most shoppers use. Start with length, because it is the single detail that decides whether a dress works on your frame, and it is the one thing a straight-on studio image hides completely. The three grids below are split by length for exactly that reason. Then read the fabric, the closure and the model's height, which is almost always stated. A dress that is described as bias-cut silk behaves nothing like one in structured cotton, even at the same measurements, and that behaviour is what people mean when they say something did not suit them.

Designer sizing is not standardised and never has been, so ignore the number on the label and find the garment measurements. Compare them against a dress you already own and love, laid flat, rather than against your body, because that removes the guesswork about ease. Three numbers do most of the work: shoulder to hem for length, the narrowest point of the waist, and the widest point across the hips. If a dress is unlined and cut on the bias, size to your hip. If it is structured with a zip, size to your ribcage. Watch for anything described as one-size or oversized, which usually means the shoulder seam sits somewhere unpredictable. And check the return terms before you check out, especially on made-to-order and final-sale pieces, because that is where online dress buying actually goes wrong.

Maxi, midi and mini are not styling preferences so much as proportion tools, and they behave differently on different frames. A maxi reads as formal almost regardless of fabric, which makes it the safest length for an event and the riskiest for anything requiring a chair and a train platform. Midi is the most demanding because the hem lands somewhere on the calf and where exactly it lands changes the whole line, so it is the length most worth measuring rather than eyeballing. Mini is the most forgiving to buy remotely, since the hem has less distance in which to go wrong, but it is the least forgiving to sit down in. If you are ordering more than one, order across two lengths rather than two sizes of the same dress. You will learn more from the comparison and return the one that loses.

Buy the fabric you can live with, then the length, then the size. Bias silk and fluid crepe forgive a lot and photograph beautifully, but they show everything underneath and they need care you may not want to give. Structured cotton and heavy jacquard hold a shape and hide more, at the cost of comfort in heat. What we would avoid ordering blind is anything strapless or corseted, because that fit depends entirely on your ribcage and no measurement chart will tell you how it sits. We would also stop ordering three sizes of one dress, which feels prudent and mostly just delays the decision. If you take one thing away, measure a dress you already love and shop against those numbers instead of against your size.