What is the best way to calculate prices/volumes "every 1 day" in any timeframe?

 
What is the best way to calculate prices/volumes "every 1 day" in any timeframe?

My idea is to count candles for 1 day, for example in 15 mins timeframe there's 96 candles. It means 96 candles is 1 day of data in 15 mins timeframe. I'm thinking till now if this is correct way or if there's an easy or natural way to do this task. I don't want to make another mistake again.