According to the United States Census Bureau, the town has a total area of , of which is land and , or 19.04%, is water. Most of Falmouth, like the rest of Cape Cod, sits on glacial sands composed of glacial outwash deposits. However, the soil in the southwestern part of the town, consisting of moraine deposits, is more rocky and dense, like the rest of New England, and many glacial erratics are scattered about, having been dropped by the retreating glaciers. The climate is temperate marine. There is no exposed bedrock. Rainfall is evenly distributed throughout the year and averages 2 to 3 in (50 – 75 mm) per month.