According to the United States Census Bureau, the township has a total area of 14.0 square miles (36.3 km2), all land.

The township has a hot-summer humid continental climate (Dfa) and is in hardiness zone 6b.

The average monthly temperature in Barto ranges from 29.4 °F in January to 74.2 °F in July.

15.1% of all households were made up of individuals, and 6.0% had someone living alone who was 65 years of age or older.

One parcel of the Pennsylvania State Game Lands Number 315 is located on Forge Dale Road north of Barto, a second parcel is located along the northern border with Hereford Township.

[7] Pennsylvania Route 100 crosses Washington Township north-to-south on its path from Lehigh County to Pottstown via Bally.