I'm using ArcGIS 10.3 and the "Legend Wizard" does not offer me a method to include symbol size within my legend. I have my symbols by color in the legend but I would like them by symbol as well, as seen in the example jpg here.
I saw a similar question from a few years ago, but the solution will not work with 10.3.
Per the additional info provided by the OP, one way to achieve a range of sizes that correspond to sized pie charts in the map display is to create a copy of the sized pie chart layer and symbolize it using proportional symbols based on the same field. For example: if pie charts are sized using attribute A, then the second layer (ordered beneath the pie chart layer) would be symbolized using proportional symbols also based on A. The next step (somewhat tedious, but AFAIK the only workaround for this), is to set the Min Value symbol size so that it matches your smallest pie chart. In the attached example, the pie chart layer is displayed using default settings/sizes based on attribute A, and the proportional symbol layer is displayed based on attribute A, using 3 classes (user defined #), with a Min Value symbol at 15pt. I didn't expect this to work, but for at least these 10 classes, the proportional symbols scaled almost exactly with the scaled pie charts. There may be some small size discrepancies, but if the goal is to convey a range of values of associated with relative sizes, I think this approach achieves the desired effect. Note that you can also choose any point symbol as your proportional display, so you could choose a half/half point that looked more similar to a pie chart if desired.
It is a little unclear what you're trying to do, but if you need to manually override the default symbol size that is generated in the legend, this can be modified by right-clicking the layer in the Legend Properties/Items tab, selecting Properties, then General, and then activating the Override Default Patch Size option (see example figure). You may have to play around with the width & height values to get the size you want. If you are trying to have the symbols scale based on some attribute value, then you will need to set up a different layer symbology (e.g. graduated or proportional values). Selecting one of these options will automatically generate scaled symbols in your legend, and can be modified in Layer Properties/Symbology.
Followup: What you are looking for is Graduated Symbols. This is a symbology option in you Layer Properties. In the Symbology tab, select Quantities-Graduated Symbols from the left menu. You can then modify your classes and the range of symbol sizes using the other options. Your legend will reflect the settings you make here.
