Raghu:
I am surprised then that if you are using a positive displacement flow meter that you are getting a RATE output from it. You should strive to get the type that gives a pulse output for each unit of flow and accumulate those pulses. The pulses relate directly to volume (or mass if your fluid characteristics are known). I worked on water meters with a PIC one time and and the pulses worked nicely.

A side discussion here is that in times gone by meters used to be set to proper readout by the selection of a pair of gears that translated the flow pulses to a particular set of units. When I worked on the PIC based meter the customer had us write the firmware in such a way that at time it was configured the user entered parameters that were 1 for 1 with the previous gear technology of teeth per gear. These were stored in a serial EEPROM. The software then had to translate the gear numbers into the proper type of scaling coefficients to do the math efficiently.
Michael Karas