|Distance:||2.1 miles (3.4 km)|
|Route outline (key)|
The B4421 is a short B-road on Anglesey.
After a couple of miles of scattered buildings the road reaches Llangaffo, where it ends on the B4419. That road TOTSOs here so the B4421 runs straight onto the B4419 towards Pentre Berw and (ultimately) the A55.