Two minis, measured
The Mini Square is 17 cm wide, 17 cm tall and 6 cm deep — the only Chanel mini with equal width and height — and it carries 54 cm of chain in a single drop. The Mini Rectangle is 20 cm wide and 13 cm tall, so it is 3 cm wider and 4 cm shorter, with a 58 cm chain. A second published set for the Rectangle quotes 20 × 12 × 6 cm, one centimetre less tall and one deeper, which is why listings for "the mini flap" can disagree without either being wrong: they are quoting different reference sheets. Both sit inside the same six-size Classic Flap ladder that runs from this 17 cm body up to the 33 cm Maxi.
What actually fits, in order
In the Mini Square and Mini Rectangle the load is a phone, a card holder and a lipstick — and the phone decides which of the two suits you. The Rectangle's extra 3 cm of width lets a large phone lie flat instead of standing at an angle, which is why it is the more practical of the pair for everyday carry. Neither takes a full-size wallet without forcing the flap, and neither closes comfortably over a compact mirror. The next step up in the same family is the 23 cm Small, which is the first Chanel size where a phone, a small wallet, keys and a compact all go in without pressure — and it is also the first size with a shoulder-strap drop reading below 50 cm.
Chain drop decides how it wears
The two minis carry 54 cm and 58 cm of chain as a single drop, which is the longest in the Classic Flap range — the Small sits at 42 cm and the Medium at 44 cm single. That length is what makes the minis read as crossbody bags on most frames and what makes them hang lower than a 25.5 cm Medium worn the same way. If you plan to shorten the chain by doubling it, the bag finishes around the waist rather than the hip, and the doubled look is the same one Chanel publishes on the Jumbo at 33 cm doubled. Chain drop is the second number to quote in a conversation, because two people asking for "a mini flap" may be picturing two different carry positions.
How to describe the mini you want
Quote width first, then width again with the chain drop — 17 cm with 54 cm of chain, or 20 cm with 58 cm — because "mini" covers both. Then say what has to fit: a large phone flat, a card holder, keys. A photo of the bag being worn the way you intend to wear it settles the strap question immediately, and a photo of the open bag with your phone inside settles the capacity question, which outer dimensions on their own cannot answer once the leather has some structure to it.