If you like a salt rim on the glasses, rub the lime around the edge of each glass and then dip the rim lightly in a plate of kosher salt.

Set aside to dry.

Combine the grapefruit juice, lime juice, triple sec, and ice in a blender and puree until smooth.

Pour into a large pitcher and stir in the tequila.

If you're not serving the margaritas in salted glasses, stir 1/4 teaspoon of salt into the pitcher of margaritas.

Serve ice cold.