Most experts agree that half-sheets, which measure about 18” x 13”, are the most versatile. Half-sheets can be used to bake cookies, roast vegetables, heat frozen French fries, and handle almost anything else in your kitchen. Baking sheet sets that include two half-sheets let you roast vegetables and toast garlic bread simultaneously without waiting for a spare sheet. You can also load a second sheet with cookie dough while the first is baking. If you choose a set with three sheets, look for the greatest total surface area.