Spark plug that suppresses pre-ignition and misfires

A spark plug comprising:

• a center electrode:
• a ground electrode that includes a facing portion facing a front end portion of the center electrode and forms a discharge gap between the facing portion and the front end portion of the center electrode;
• a cylindrical insulator that accommodates the center electrode therein with the front end portion of the center electrode being exposed from a front end of the insulator;
• a metal shell that accommodates the insulator therein;
• and
• a cover portion that covers, from a front end side of the spark plug, the front end portion of the center electrode and the facing portion of the ground electrode to form a pre-chamber,
• the cover portion including an injection hole that is a through hole,
• wherein the insulator includes an outer peripheral surface that is exposed to the pre-chamber,
• the cover portion includes a portion that is exposed to the pre-chamber,
• the metal shell includes a portion that is exposed to the pre-chamber, and
• wherein when a surface area of the outer peripheral surface of the insulator is a first surface area A (mm2), and a total surface area of the portion of the cover portion and the portion of the metal shell is a second surface area B (mm2), a relational expression 1 below is satisfied:
• 0.10<A/B<0.70.