when It comes to astrological benefits of yellow sapphire or rather any gemstone, its not just the weight of the gemstone that matters.
Quality of a gemstone which includes its **clarity, lack of flaws & Treatments, cut and color also matter. **
In general, **Gemstone of 1/4th to 1/5th of body weight in carats with 2.5 carat being the min. weight is recommended depending upon quality of gemstone for the optimum astrological benefits.**
Astrological benefits also depends upon the level of belief that you have on Gemstone. **Wear it and forget it to gain maximum astrological benefits.**