I think the question is about choosing the correct airfoil chord.
If that's the case, then a simple rule of thumb is 10% "solidity". In aerodynamics, the solidity of a rotor is the percent of the swept area that is actually taken up by material.
For example, if each blade is 1m long, and has a chord of 10 cm, then three of these blades will have 0.30 square meters of surface area. The whole swept area will be a circle of 2m diameter: 3.1 square meters. In that case, the solidity ratio is 0.3/3.1, or 9.5%, which is pretty close.
The chord can vary from root to tip. If you want a narrow tip, then the root must be bigger to give the same area and solidity.
Solidity of 10% is sufficient for many types of wind generator, but it is a secondary factor beside the diameter. Most people assume that a certain size of rotor means a certain power output, but matching the prop to a generator can be a challenge if you are attempting to get it right "on paper". However, a diameter a few percent larger is MUCH better than having the chord wrong by a few percent.
I spent a year fiddling with a motor conversion generator getting it to match with the 8-foot prop. Fortunately in my case I had "too much" prop to begin with, so improvements to the generator brought them in line.