Is there a chart somewhere that indicates how big a leg to use on a table of a certain size to support a specific weight?
(Furniture Making Forum)
From contributor M:
I do not know if any charts are available, but I have found that leg size is not as important as the rail to leg joint and the strength of the rail itself. If you have an idea of the weight that a table may need to support, and provide some info on the material that will be used, plus the table construction method, maybe we could give some suggestions.
What size leg are you thinking about using and what wood species? I believe the 3" apron would be fine, and look better than a 4" on a table this small. You could easily get a 2" tenon, unless you choose to go the full 3". We make a lot of our tables from heart pine, usually 1 1/4 x 2 or 1 1/4 x 3. On a small table we would go with the smaller size and taper down to 1 1/4 x 1 1/4 (approximately) at the floor end. I would not hesitate to put the marble top on this size leg.
One thing is most people do not put a lot of extra weight on a marble top. Plus we see a lot of antique tables in homes and shops that have small legs carrying marble tops. Most that were made correctly and have been cared for are still working quite well.
However, in a table, lateral forces play the dominant part. The table has a stone top, is loaded with food, dinnerware, etc, and someone decides to scoot it over a foot for more chair clearance on one side. Not pick it up and move it, but scoot it across the floor. Scooting that table 12" will stress the leg to apron joints and also cause the legs to flex. The 1" x 1" cross section leg will shudder and shake, and if the grain is less than continuous along the length, may separate. A 4" x 4" leg will not flex at all.
In a static situation, both will support the weight, but the flex of the 1x1 legs will cause the table to feel wobbly and insecure long before a fatal scoot. Note that antique dealers, conservators and fine makers and collectors all move such things with care and knowledge, while the average user just needs to get three more people seated over there.
Your quest is for balance of form and function. What will surely satisfy the function may not be a pleasing form, and the perfect form may not satisfy the demand for function. As the designer, you must weigh the merits of any design on the twin scales of form and function to arrive at a successful design.
One way to do this is to look for historical precedent. The classic Hepplewhite leg tapered on two surfaces to half its cross section as it hit the floor. This gives good heft at the joint, where flex would be least tolerated, and gets thinner and more graceful as it approaches the floor, where the leverage is the least and the need for appearance dominates.
In short, there is no formula for this, thankfully. As a result, there are thousands of solutions, many are both attractive and functional. Vive la differance.