These examples show how you can use the CryptoCompare API.
Read official UPDATED documentation here.
[(total volume across all coins in BTC - total volume for BTC/USD pair) * current BTC/USD Price] + direct volumeto BTC-USD
This is to give a closer approximation of the total volume in USD as the price will change over the period giving a different value. It is important to note that this is the best approximation for the total volume in USD but is NOT an exact solution.