I have tick data in the following format... YYYY/MM/DD hh:mm:ss.ss1 AskPrice1 BidPrice1 YYYY/MM/DD hh:mm:ss.ss2 AskPrice2 BidPrice2 YYYY/MM/DD hh:mm:ss.ss3 AskPrice3 BidPrice3 ... .. . Does anybody know of a standard formula or method to derive a proxy for the Buying and Selling volume from this type of data over some period of time, say like every 5-15 minutes? I understand that some methods average the Bid and Ask and if the average is closer to the previous ask it's Buying and conversely if the average is closer to the previous Bid it's selling. This may work but I thought I'd see if there was a standard method for estimating. Before you tell me it's not the true volume, Yes I know that. Again I am hoping to estimate the Bid/Ask volume from the data.