What matters
Medium Post Image dimensions at a glance
Medium article images at 1400×1050 display at the top of stories and in feed preview cards. The 4:3 ratio fills the reading area without overwhelming the text.
Articles with compelling feature images get significantly more reads from the Medium feed. The image is the primary draw before readers commit to the text.
Small images look blurry when Medium stretches them to fill the content width. Very wide or tall images get cropped awkwardly in feed preview cards.