The India-based Neutrino Observatory (INO) collaboration is planning to setup a magnetized Iron-CALorimeter (ICAL) to study atmospheric neutrino oscillations with precise measurements of oscillations parameters. The ICAL uses 50 kton iron as target mass and about 28800 Resistive Plate Chambers (RPC) of 2 m × 2 m in area as active detector elements. As part of its R&D program, a prototype detector stack comprising 12 layers of RPCs of 1 m × 1 m in area has been setup at Tata Institute of Fundamental Research (TIFR) to study the detector parameters using cosmic ray muons. We present here a study of muon flux measurement at sea level and lower latitude. (Site latitude: 18 • 54 ′ N, longitude: 72 • 48 ′ E.