Rock Shoes: Scarpa recommends you downsize 1/2 to 2 full sizes from street shoe size, though downsizing depends on shoe model, intended use and personal preference. Mountaineering: Scarpa recommends you upsize 1/2 size or more depending on desired fit. Scarpa plastic mountaineering boots are based on the UK sizing scale. Ski Boots: All Scarpa ski bootsare measured in Mondo sizing.Highlighted (or not) sizes share the same shell size; the liners are lasted for each 1/2 size. Some skiers may want to downsize up to 1 full Mondo size, depending upon personal preference.