Usually width comes first, then height when people write dimensions for 2D items like images, screens, or banners. For 3D objects, the common order is length × width × height.

Quick rule

  • 2D: width × height.
  • 3D: length × width × height.

Why it varies

Different fields use different conventions. Design and graphics often use width first, while packaging and technical specs often use length first for 3D objects.

Easy example

  • A poster might be 24 × 36 meaning 24 wide, 36 high.
  • A box might be 10 × 8 × 6 meaning length, width, height.

If you want, I can also give you the rule for photos, screens, boxes, and clothing sizes separately.