36" is about the maximum width that can fit, but 24" is about the maximum depth; after that it tips off your lap. For many people 18-22 is realistic. Somethin

36" is about the maximum width that can fit, but 24" is about the maximum depth; after that it tips off your lap. For many people 18-22 is realistic. Something this size: https://m.staples.com/Flipside-Chalk-Board-24-x-36-Black/product_138982 https://m.staples.com/Flipside-Chalk-Board-24-x-36-Black/pro...