Adders are key components in digital signal processing, performing not only addition operations, but also many other functions such as subtraction, multiplication and division. The difficulty with comparing adder structures from different sources is that quite often different implementation techniques and technologies have been used in the design. A second problem that arises when comparing structures is that several different measurement techniques may have been used, the target technology can differ and key features may not been measured. Therefore, this paper will investigate the seven most commonly used adder structures in a way which makes them directly comparable. This is achieved by implementing all adder structures with the same technology, the same level of abstraction and then using the same set of tools to determine the features of each of the designs.