How do you calculate volume intra-day?

For example, we want to buy a stock if volume picks up to the two million range. Problem is, you don’t know what the real volume will be until the end of the session. By the time you know the volume, the stock has run $5. We handle this dilemma by knowing the stock’s average volume, its previous day’s volume, the overall volume in the market that day (is it heavy, light, what?), and our target volume. We tell our brokers what our target volume is for the day. We can check current volume by that target by doing some math. Just multiply the volume in the first hour by the number of hours left in the trading day. Will it make it if it keeps that pace? It is not foolproof-you can have a drop off in volume or you can have a burst in volume later in the day. In the normal situation it usually works.