How to choose a bag size you will not regret
Almost everyone buys a bag that is slightly too big. It happens for an obvious reason: we pack for the day we imagine, not the day we actually have.
There is a cheap way to avoid this, and it takes about fifteen minutes.
Start with the pile, not the bag
Empty whatever you currently carry onto a table. Everything. Then split it into two piles:
- Pile A — things you touched today
- Pile B — things you have not touched in a week, but keep "just in case"
Pile B is usually about a third of the volume and contributes almost nothing. Most people can move two thirds of it to a desk drawer without noticing any loss.
Then measure the right way
Do not measure the bag you own — bags are padded, structured, and unreliable for this. Stack Pile A into a rough block and measure the block:
- Length — the longest item, usually a laptop or a water bottle
- Depth — the thickest item, usually a toiletry pouch or notebook
- Height — the tallest stack
Add roughly two centimetres to each dimension. That is your real minimum. Anything more than four centimetres beyond it is space you will fill with things you do not need.
The three-litre rule
If you remember one number, remember this: roughly one litre of capacity per hour of daily carrying is a comfortable baseline. It breaks down like this:
- Up to 4 litres — phone, wallet, keys, a small notebook. An evening bag.
- 5–8 litres — plus a water bottle and a tablet. Most people's daily bag.
- 9–14 litres — plus a 13-inch laptop and a light layer. A commute bag.
- 15 litres and up — a 16-inch laptop, gym kit, or a weekend's clothes.
The best test of a size is whether it feels slightly too small on the day you pack it. It will feel exactly right on every other day.
Consider how you travel, not just what you carry
Three questions that change the answer more than capacity does:
Do you walk or drive? Walkers should weigh weight distribution more heavily than volume. A heavy bag on one shoulder over two kilometres is a different object than the same bag in a car.
Do you need both hands? If you commute at rush hour, carry a coffee, or take public transport, a structured top-handle bag will spend its life on your forearm. A crossbody strap solves this, and it is worth choosing a bag that has one.
Does it need to sit on your lap? If you work in cafés or on trains, a wide bag becomes an obstacle. Narrow and tall usually beats wide and shallow.
One last check
Before you commit, put your heaviest item in the bag and carry it around the shop for five minutes. Not thirty seconds. Five minutes.
Handles cut into a bare forearm. Straps slip off a shoulder that has nothing to grip. Flaps are awkward when they open towards your body. None of these problems show up in a mirror, and all of them show up in the first week.
Buy the size your actual day needs. You can always add a tote for the rare big day — you cannot shrink the bag you bought for a fantasy one.