The short answer: a pouch holds a phone and a card, a clutch holds a phone, a lipstick and keys, and a mini bag holds all of that plus sunglasses and a small hairbrush, with a strap so your hands stay free. That is the whole hierarchy, and it is worth knowing before you buy, because almost every disappointing small bag is a bag bought one size below the job.

I use all three and I use them for completely different evenings. What follows is how I actually decide, based on the two measurements that matter more than the name on the label: internal width, and whether there is a strap. Everything else is decoration.

Below, the three smallest bags in order of capacity: the pouch, the clutch, the mini bag. Staud, Mansur Gavriel, Cult Gaia and Khaite are all here, and DeMellier takes the Label Love for making a mini that still holds a phone and keys.

A pouch is the smallest useful bag and the one most people underestimate, because it is not really a bag at all. It is a way of carrying the contents of a bag inside something else, or of carrying almost nothing on purpose.

Buy one if you already carry a tote to work and want your essentials findable inside it, or if you want a hands-free evening with a phone and a card and nothing more. The good ones are flat rather than boxy, have a real zip rather than a magnet, and come in leather or a woven that holds its shape when empty. Mansur Gavriel and Nili Lotan make the elegant versions, Hammitt and Jenni Kayne the practical ones, and Frēda Salvador's is the cheapest useful thing in this issue. Skip any pouch with a wrist strap so thin it will not survive being pulled.

A clutch is the shape people buy for one wedding and then never use again, which is a shame, because the modern versions are far more wearable than that. The distinction worth drawing is between an envelope clutch, which holds a phone flat and nothing thick, and a soft or slouchy clutch, which will take a phone, a lipstick, keys and a folded card holder.

Two practical notes. Check that your actual phone fits in the actual bag, since large-format phones no longer fit many older clutch patterns. And strongly prefer a convertible style with a removable chain or strap, because the reason clutches sit unused is that carrying something in your hand for four hours is genuinely annoying. M.Gemi and A.L.C. do convertible well, DeMellier's Vancouver is the one I would buy to keep, and Khaite and Nili Lotan are there if this is a considered purchase rather than a practical one.

The mini bag is the one that earns its place, because it does almost everything a medium bag does while looking deliberate. The useful range is roughly 16 to 22 centimetres wide. Below that you are buying jewellery. Above it you have simply bought a small bag, which is fine, but price it accordingly.

What to look for: an adjustable strap that can be worn short on the shoulder and long across the body, a flat base so it sits rather than rolls, and a closure you can open one-handed. Structured styles hold more than they appear to because nothing collapses inward. St. Agni, Staud and Rails cover the everyday end, Joseph and Mansur Gavriel the leather investment end, and JW PEI does a genuinely good cheap version if you want to test the shape before committing.

DeMellier is the brand I point people to when they want one small leather bag to keep, and the reason is boring and good: the range is deliberately narrow. There are about twenty styles, each named after a city, each offered in a few clean sizes, and they do not chase a new silhouette every season.

The practical result is that sizing is legible. The New York is the mid-size everyday shape, the Nano Montreal is the smallest thing that still holds a phone, and the Midi versions of Hudson and Brooklyn sit between a mini and a real day bag. The leather is smooth calf that scuffs less than pebbled at this price, and the shapes hold up empty. If you only want one, the New York Crossbody is the least fussy and the most useful. It also happens to be the price band where a small bag stops being disposable.

What is on my radar right now, all of it small, all of it strapped.

Dagne Dover Micah crossbody in camel, the cheapest thing here and the one that would survive a commute.

DeMellier Siena Crossbody, the bucket shape for people who find bucket bags too casual.

Staud Alden shoulder bag, a proper shoulder shape with a short strap, which is having a real moment.

St. Agni Connolo in black, quiet and the right size for the 16 to 22 rule above.

Mansur Gavriel Classic Crossbody, the one to buy if you want to stop thinking about bags.

Beek Willet woven shoulder bag, texture instead of hardware.

Ganni mini top handle Apo-G, for when you want the bag to be the interesting part.

M.Gemi Ursula baguette, because the baguette is back and this is the wearable version.

How I decide between the three, every time.

Empty your current bag onto a table. Whatever is left after you remove what you never use is the volume you actually need. It is almost always smaller than you think and larger than a clutch.

Always choose the strap. A removable strap costs nothing and doubles the number of nights you will use the bag.

Measure the phone. This one sentence would prevent most small bag returns.

Structure beats softness in small sizes. A soft mini bag looks empty and holds less, because the sides fall in.

If you take one thing away: buy the mini bag with a strap, not the clutch. The clutch is the one you will admire in the wardrobe, and the mini bag is the one you will actually leave the house with.