The position sizing function will help you auto-fill the quantity based on the percentage entered and the availability of margin.
For instance, Mr. Joshua, a client of Fyers, has a balance of ₹1,00,000 in his trading account, and his trading pattern has always been to invest 50% of the funds every time he places the order. So, he sets the pre-fill quantity at 50%. The system will pre-fill the quantity at 50% of the funds available in his account whenever he places an order.
Click on the ‘User Settings’ option available on the order window as displayed in the image below:
The quantity will be pre-filled based on the set percentage of the available margins as displayed in the image below: