The Kleine Sinn, the source of the Sinn, rises in the Bavarian Rhön and flows into the Schmale Sinn at Ziegelhütte, which in turn joins the Sinn at Zeitlofs. 
The Sinn itself is 50 km long and has its source in the Bavarian Rhön at the foot of the Kreuzberg near the municipality of Wildflecken. The narrow Sinn has its source below the Dammersfeldkuppe. Both join behind Zeitlofs on the Hessian-Bavarian border and flow into the Franconian Saale in Gemünden just 700 meters before flowing into the Main. Tributaries of the Sinn are the Jossa and the Gronau. Notable towns along the course of the river, in whose valley the Würzburg-Fulda railroad line temporarily runs, are: 

Schmale Sinn: Weichersbach, Mottgers, Oberzell, Kothen and Speicherz 

Sinn: Wildflecken, Oberbach, Bad Brückenau, Zeitlofs, Jossa, Mittelsinn, Burgsinn, Gemünden

The Schmale Sinn is located on the premium hiking trail Extra tour "The Mottener".