Why vertical pins win
Pinterest's feed is a vertical scrolling grid. Tall images (2:3 ratio at 1000×1500 px) take up more screen space and stop the scroll. Square pins at 1000×1000 px work but get less visibility in the algorithm.
Long pins (up to 1000×2100 px or 1:2.1 ratio) are ideal for recipes, DIY tutorials, infographics, and before/after transformations. Pinterest may truncate pins taller than a 1:2.5 ratio, so stay within 1000×2500 px max.
Set dimensions, export, and move to the next step.