The three sizes that matter
Ignore the catalogues offering nine sizes. A house move needs a small box, a standard box and a large box, and the whole job comes down to matching weight to volume. A box that is the right size for the item is a box that gets carried safely and stacks squarely, and a van packed with squarely stacked boxes takes one load instead of two.
Small or book boxes
Roughly 30cm x 25cm x 25cm. For books, tinned food, tools, records, tiles, anything with real density. The size is a deliberate constraint: fill a standard box with hardbacks and it comes out at 25kg or more, which is how backs get hurt on staircases and how box bottoms let go halfway across a pavement.
Standard or medium boxes
Roughly 47cm x 31cm x 25cm, about 35 to 45 litres. This is the workhorse and it is what any box count means unless it says otherwise. Kitchen cupboards, wardrobes, bathroom cabinets, the contents of a sideboard, toys, shoes. Around two thirds of a typical house ends up in this size.
Large boxes
Roughly 46cm x 28cm x 28cm and up. Reserved for things that are bulky and light: duvets, pillows, cushions, coats, lampshades, soft toys. The temptation is to fill one with whatever is left in the room, which is exactly how you end up with a box nobody can lift. If it is heavy, it is in the wrong box.
Single wall or double wall?
Corrugated board is a wavy layer of fluting sandwiched between two flat liners. Single wall has one of those sandwiches, double wall has two. That second layer is what stops a box bowing outwards when there are four more on top of it, and it is the reason a double wall carton survives three or four moves while a single wall one is finished after the first.
For a house move, buy double wall for anything going in the van and do not agonise over the rest. Ours are double wall, and the pack below is the same specification.
Box quantities, honestly
Everyone underestimates, and everyone underestimates the kitchen specifically. A large kitchen with a stocked pantry, a full set of pans and a cupboard of appliances is thirty boxes on its own, which is more than most people budget for the entire downstairs. Put your rooms into the packing calculator before you order anything.
Order about ten per cent more than the calculator says. Flat packed boxes take up almost no space, and an unused one is a far smaller problem than running out at nine o'clock the night before the move.