Lopez is one of the largest municipalities in the province and has a total land area of 395.1 square kilometers representing 4.53% of the total land area of the province of Quezon.
The terrain generally ranges from 345 to 399 metres (1,132 to 1,309 ft) above sea level with rugged mountain areas. Coastal areas deviate from plain to hilly terrains. Rivers, streams and springs abound throughout the municipality, but the most prominent is the Talolong River.
It is bordered by the municipalities of Catanauan and General Luna on the south, Macalelon on the south-west, Calauag on the north-east, Gumaca on the west, Buenavista and Guinayangan on the east.