Find out their shoe size, not their sock size
Each maker’s chart maps shoe sizes to its own letters, so a medium at one brand is a large at another. Ask for their shoe size (or check a pair of their shoes), then read it on the chart for the brand you buy.
Shoes decide the height
Trail runners: a no-show, ankle or quarter sock. Boots: a micro crew or crew. Not sure: a micro crew covers both.
A safe middle choice
Medium cushion and a lightweight or midweight knit suit most three-season hiking. Merino is the most common hiking fiber; pick a wool-free sock if they avoid wool.
Make exchanges easy
Unworn socks can usually be returned or exchanged for a different size within the shop’s window; worn socks usually cannot. A long guarantee, such as Darn Tough’s for life, also helps the gift last.
Designs
Many makers sell patterned versions of the same sock (Darn Tough and Smartwool have dozens). The pattern does not change the fit; the model, height and cushion do.