A spark plug helps to prevent an insulator from being damaged due to deterioration caused by external force. The spark plug includes a tubular insulator, and a tubular metal shell secured to an outer peripheral surface of the insulator by crimping. The tubular metal shell includes: an inner peripheral surface in which powder for sealing is filled between the outer peripheral surface and the inner peripheral surface; a tool engagement portion overhanging in a polygonal shape; and a crimped lid disposed at an end portion of the metal shell coupled to the tool engagement portion, the end portion being bent toward the outer peripheral surface of the insulator by crimping. A relationship between a length L and a thickness t satisfies 2.50<=L/t<=3.10, the length L being along a shape of the crimped lid from the tool engagement portion to the insulator in a planar surface that passes through the axis, the thickness t being a thickness at an intermediate portion of the crimped lid.