Knee-high socks

The length that has to hold itself up all day.

A knee-high finishes just below the kneecap. Unlike every shorter length, it crosses the widest part of the calf, so the same sock has to be loose enough to pull on and tight enough not to sag by lunchtime.

That balance is a grading problem, not a materials problem. The leg is knitted with progressive tension that changes along its length, and the top band does far less of the work than buyers usually assume.

Calf circumference, not shoe size. Two people with the same feet can differ by ten centimetres at the calf. A knee-high graded only on shoe size will fail on one of them.

What goes underneath. A shin guard, a boot shaft or nothing at all. Team socks are knitted wider through the shin for this reason, and a formal sock knitted to the same pattern will fall down.

Top band construction. Wide soft welt for comfort, or a firmer band for hold. A band that grips hard enough to stop a sagging sock will leave a mark on the leg, so the hold should come from the leg tension instead.

Elastane distribution. State whether you want it even along the leg or concentrated below the knee. This single choice is most of the difference between a sock that stays up and one that does not.