Editorial disclosure: this guide was prepared for SuperReps by an administration-managed editorial profile. It is not a personal purchase or a first-hand product review.
“The insole is 28 cm” is not a complete sizing answer. It is a useful comparison only when both people measure the same thing in the same way.
Photograph the method
If the insole is designed to come out easily, place it flat beside a ruler and photograph the full length. Do not tear out a glued liner. State whether the measurement follows the curve or runs straight from the rear edge to the longest point; do not mix methods.
Compare with your own comfortable pair
Record the model, tagged size, insole length, approximate width at the widest point and sock thickness. Note a raised heel cup or strongly curved edge, which can make a simple length comparison misleading. Two equally long insoles do not guarantee equal usable space.
Explain the actual fit problem
Is the heel slipping, the forefoot squeezed, the toes touching, or the upper pressing down? These are different problems. Ask for the measurement you need rather than a general “true to size?” vote.
Use a familiar pair as the baseline and treat insole dimensions as supporting evidence. They cannot reliably predict internal volume, stretch or comfort. If the insole cannot be removed, say so and request a different comparison instead of inventing a measurement.