tabber,
You may not be getting a response to your question because it is a little more complicated than a simple ratio that would require a certain footer for a given height. A demo program I downloaded from Retain Pro was helpful to me to assess the walls I'm building. I live in Arkansas and around here there have been a lot of DIY block walls built. Most of them have failed or are in the process of failing. Best I can tell, those that stood up over the years were built on a substantial footer and the block cavities have rebar and concrete. Steel stubs up from the footing to lock the wall to it in many of the block cavities. The good walls that are over 3 feet high were made with 12" block and they all have a system to prevent the ground behind the wall from becoming saturated with water. Not a cheap thing to construct. Lately, a lot of homeowners have built walls using the modular blocks that lock together. Close attention to the details will bring most DIY walls of this type to a good result. But they are what they are. If you like the look, it's not a bad way to go. If you want a true vertical wall that can have a finish of stone , tile, or some other material, then you have to look elsewhere. Timber walls are another possibility that some choose. But they aren't a permanent solution. The life span of a timber wall is also shortened if you have a long season where the ground is warm and you garden on the up side keeping the ground wet and fertilized. In the end I chose to do poured concrete walls. Most would say that this type wall is beyond a DIY project, but in my second year of wall building, I would say that there are no special skills needed, nor is the cost of tools that much more than needed for other types. One might call it an advanced DIY project, not for a beginner. I didn't have experience with concrete when I started but I did have a lot of DIY projects and was well experienced in working with wood. Most would do well to keep their wall heights to 3 feet and under. Keep in mind that down here the ground does not freeze more than a few inches deep, something that might be a major problem for those in colder areas. I now have about 200 feet of wall up with another 125 to go. One of the things I like about poured concrete is that I don't have a lot of really heavy lifting to do. There is a lot of labor, but the form panels and other materials are not much more than 20 pounds, something an older man can handle. James | 
