For years, I've been drawing out my vegetable gardens on graph paper to plan where and how much of everything to plant. That's one way to do it. There are also several pieces of software you can purchase for planning a vegetable garden, but I'm cheap--that's probably one of the last things I'd spend my money on. However, I found a very good free online vegetable garden planner at the Gardener's Supply Company website. The site offers several pre-designed garden plans, including a design for a salad garden and (perfect for the busy gardener) a "plant it and forget it" garden, or you can design your own garden by simply dragging and dropping different vegetables onto the plan. It will show you how many to plant in a given area. One drawback is that the designs are all based on a 3 by 6 foot garden bed, but it is still a good tool if, for nothing else, to see how many vegetables to plant. The plans all seem to be based on the Square Foot Gardening method, which is actually one of my favorite ways to plan a garden. It's a fun little tool to play with, and it makes it easy to efficiently plan a garden bed.