Is this STT calculation correct?

Take for example,

Buy value : 10k
Sell Value 20k

Assuming that there is 100% profit.
This is delivery trade and NOT intraday.

STT Calculation 1
Average of buy and sell is 15k
0.01% = 15rs (all together)


STT calculation 2
Buy value = 10k, → STT = 10rs
Sell Value = 20K → STT = 20rs
Total STT = 10 + 20 → 30rs.

Which one is correct way of calculation for delivery trade ?

This is the correct method.
For more Information refer zerodha calculator for more clarity.

The second method is correct. The method for levying STT is also mentioned in Rule-3 of Securities Transaction Tax Rules, 2004 -

Value of taxable securities transaction.

3. For the purposes of clause (c) of section 99 of the Act, the value of a taxable securities transaction, being a purchase or sale of an equity share in a company or a unit of an equity oriented fund, entered into in a recognised stock exchange, shall be determined in the following manner, namely :—

     (b ) where the equity share or unit is purchased or sold by a person in the trade-for-trade settlement mode, the value of the taxable securities transaction shall be the price at which the equity share or unit is purchased or sold;

“trade-for-trade settlement mode” means a mode of settlement of transactions in a recognised stock exchange where each trade is compulsorily required to be settled by actual delivery;

Thanks for the clarification @Prayag @Ranjan5