3-Methylheptane is a branched alkane isomeric to octane. Its structural formula is CH<sub>3</sub>CH<sub>2</sub>CH(CH<sub>3</sub>)CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>. It has one stereocenter.
Its refractive index is 1.398 (20 ðC, D).