From the manufacturer:
• Easy to carry to games, easy to setup, small so it doesn't dominate your table!
• +9 against metal dice damage to wooden tables
• Quiets loud dice rolls on plastic tables
• Keeps dice from flying off the table or hitting your minis
• High quality materials, strong enough for metal dice
• 8.5" x 11" (same WxL as US Letter Size Paper) when flat, smaller but taller when set up
• Fits easily into backpacks and folders
• NEW Durable magnets ensure a perfect setup and seamless takedown without the hassle of snaps
8.5 x 11 inches when flat. In "Dice Tray" mode it is 5 x 7.75 inches with 1.75 inch high walls.