Take how many coins have been traded during that time and divide by the number of coins that have been minted in the same time.
Trading does not equal demand. Trading volume indicates nothing more than traders trading, BTC on a dive for example will have vast trading volume, yet smaller trading volume on a rise, then random slow days and random high purchases. It's a rough guide to traders speculative sentiment, or post reactionary to bad/good news and little more.
You measure demand roughly, by usage. What percentage of the currency is floating, in the virtual pocket of users who need or want to use it for some purpose. The higher that percentage, or the faster it's increasing, the more real demand there is.