MEDIUM: Can fit a water bottle, snacks, a book, wallet, sunglasses and a 13” Macbook snugly. Measured 10.5” wide across the base, 15” wide across the top, 5.5” deep, and 12” tall. 

LARGE: Fits a water bottle, snacks, book, wallet, sunglasses, back-up shirt, and a 15” Macbook snugly. Measures 11” wide across the base, 18” wide across the top, 6” deep, and 12” tall.