SMALL: Can fit a water bottle, snacks, a book, wallet, sunglasses, and a Kindle. Measured 9.8" wide across the top and bottom, 4.5" deep and 7.5' tall.
MEDIUM: Can fit a water bottle, snacks, a book, wallet, sunglasses and a 13” Macbook snugly. Measured 13.8” wide across the top and bottom, 5.5” deep, and 10.6” tall.
LARGE: Fits a water bottle, snacks, lunchbox, books, small makeup bag, back-up clothing, and a 15” Macbook snugly. Measured 16.1” wide across the top and bottom, 7.5” deep, and 13.4” tall.