All six Flap sizes, measured
The six sizes below are the ones that appear most often. Width, height and depth are listed as they are quoted by collectors' references; strap drop is given doubled and single where both are published. Note that Small and Medium are close in width — the difference buyers notice most is height and depth, not width, which is why a Medium looks noticeably bulkier on the shoulder than a Small even though the width figure is only about 2.5 cm apart. Measurements are quoted from published references and can shift slightly between seasons and hardware generations, so treat them as the figure to confirm rather than a fixed constant.
What actually fits, by size
The Mini Square and Mini Rectangle carry a phone, a card holder and a lipstick, and little else — the Mini Rectangle fits a phone more comfortably because its extra width lets the phone sit flat. The Small adds a small wallet and a compact. The Medium is the first size where a full-size wallet, phone, keys and a small pouch all fit without forcing the closure, which is why it is the size most buyers settle on. The Jumbo takes the same contents plus a small tablet or a folded scarf, and the Maxi will hold a laptop sleeve in some configurations. Depth is the variable most people underestimate: the Jumbo and Maxi are both about 10 cm deep against the Small and Mini at 6–8 cm, and that depth is what makes the larger bags feel like an everyday carry rather than an evening bag.
Lambskin, caviar and how the material changes over time
The two surfaces buyers ask about most behave differently. Lambskin is softer and takes a deeper sheen, but it marks more readily and shows light surface scuffs. Caviar is a pebbled calfskin finish: the grained surface hides small marks better and holds its shape more firmly, which matters more on the larger sizes where the bag carries weight. Patent finishes are firmer again and show fewer creases but are the least forgiving of scuffs. If you are choosing between two otherwise identical pieces, the surface type will affect how the bag looks after a year of regular use more than the size will.
Describing the size you want so the answer matches
Size names alone are not enough in a conversation, because "Medium" and "Large" are used interchangeably for the same 25.5 cm size in different references. Quote two numbers instead: width in centimetres, and whether the strap is worn single or doubled. The strap is the second half of the sizing question — a Medium worn doubled sits at roughly the same position on the body as a smaller size worn single, so two people asking for "a Medium" may be picturing two different carry positions. If you have a photo of a bag being worn the way you intend to wear it, send that as well: it resolves the strap question immediately.