The source is 1.2 km southeast of the village Görzhain (municipality Ottrau) in a clearing of the northern flank of the Frohnkreuzkopf (about 530 m above sea level (NN)), the western spur of the Rimberg (591.8 m), at about 395 m elevation.

It passes along the settlement Bahnhof Ottrau and a number of watermills (Boßmühle, Steinmühle, Lenzenmühle, Schneidmühle) and the village Kleinropperhausen.

Then the Grenff flows through the riverside town Nausis, past the Bruchmühle, Neukirchen, and Rückershausen, after which it passes the Sängermühle, and Riebelsdorf.

At the village of Loshausen (Willingshausen municipality) it flows into the Eder tributary Schwalm that comes from the south, after descending 181 m in elevation.

[1] Its tributaries are orographic allocation (l. = on the left side, r. = on the right side) , river length and confluence location, Grenff river kilometer (starting from the mouth )[1]: Media related to Grenff at Wikimedia Commons