Short Answer: 422mm length, 94mm height (80mm height or less recommended for best cooling)
Details: The Y40 is currently capable of supporting graphics cards up to 4.5 slots, but we typically do not recommend exceeding 4 slots (80mm) as it may negatively affect the overall temperature of your case. We highly recommend looking into hybrid cards such as the MSI Liquid Suprim 40 Series cards, or custom water-cooling if you're looking to use cards that exceed the advised reservation of 4 slots (80mm).