At present noise pollution in Thailand has become a big social problem and getting more serious as other kinds of pollution especially in Bangkok Metropolitan, the center of economic and social development. It has been planning to construct many projects for example express way, outer O-ring road, mass transportation system and the second Bangkok International Airport, in order to support the expansion of the city in the future. To know the situation of noise problems in Bangkok Metropolitan Area, the Pollution Control Department measure Leq (24 hrs) at several sites every year according to ISO. But it is difficult to get the real (Leq 24 hrs) values for the whole of Bangkok because of its large area. The possible short-term method has to be investigated. From the study, the result show that if ±3 dB(A) error is acceptable, the estimated Leq (24 hrs) value which calculated from a pair of the measurement values of Leq (10 min) during 10:00 to 18:00 o’clock and 22:00 to 0:00 o’clock can effectively represent Leq (24 hrs