Furniture dimensions don’t come out of the air. They come out of heavy research that, thankfully, many people have already done for us and written books Furniture dimensions don’t come out of the air. They come out of heavy research that, thankfully, many people have already done for us and written books on. Dimensions for furniture have been standardized over the years to fit the average-size person. While you can customize furnishing to fit your personal needs, here’s a list of commonly used dimensions to help you plan your next project.