The five presets ImagePipe provides (product_card, product_page, category_banner, manufacturer_logo, mobile_thumbnail) are calibrated for standard WooCommerce spots. A custom theme, a 5-column catalog grid instead of 4, a full-width zoomable product gallery, almost always displays its images at real dimensions that differ from the defaults.
To find the right target dimension: inspect the displayed element in your browser's developer tools (the actually rendered CSS width and height, not the original file size), then multiply by 1.5 to 2 to cover high pixel-density screens (retina). A systematic ×2 factor also doubles the weight of every generated variant, for a sharpness gain rarely perceptible beyond ×1.5 on a typical product photo.
Reconfigure an existing preset rather than creating a new one: change product_card's target dimensions directly in the settings rather than multiplying custom presets for each spot, simpler to maintain over time. Variants already cached under the old setting stay valid until explicitly cleared (see the guide on clearing the cache after a theme change).
The resize mode matters as much as the size itself: a catalog grid with product photos of varying ratios almost always needs Cover or Crop to stay visually consistent, while a category banner often needs to stay in Contain mode so the visual is never cropped. A preset with the wrong size but the right mode is usually more visually acceptable than the reverse.