Cushion is a location, not only a level
A label may describe cushioning underfoot, around the heel and toe, at the ankle or throughout the foot and leg. Ask which parts are padded. Darn Tough’s Light Hiker 1972 describes underfoot, ankle and Achilles cushion; REI C10726 names the heel, toe and bottom.
Keep each brand’s scale intact
Smartwool distinguishes light, full and extra cushioning; its Classic Full and Classic Extra pages also use medium- and heavy-thickness language. Darn Tough separates yarn weight from cushion level. These terms are not one calibrated cross-brand thickness scale.
When footwear fits closely
Check how the current pair sits before adding fabric. A light or liner construction can be a starting point for comparison, but a label cannot certify toe room or pressure. Try the exact size with the intended insole and lacing.
When there is room for more fabric
A full or extra-cushion construction may match a preference for more padding, provided the complete shoe-and-sock combination still fits. Do not use a thicker sock to conceal a shoe-fit problem without checking heel position and toe movement.
Compare like with like
Put two exact models side by side. Look at the weight label, cushion level, cushion location, cuff height and layer count. A two-layer sock and a full-terry single layer can occupy space differently; this guide does not assign millimeters that have not been measured.