Selfoss is 60 km from Reykjavik on Route 1, the Ring Road. By car, it is about 45 minutes. Buses run several times daily from Reykjavik's BSÍ terminal; the journey takes about an hour. The town is on the route for most south Iceland bus services, making it a natural stopping point.
If you are driving the Ring Road in either direction, Selfoss is the first or last major town depending on which way you are going. The surrounding roads are well maintained year-round, though winter conditions on mountain routes (to Þórsmörk, for instance) require caution.