70 miles taking this route: Take M876 & A876 PERTH (via M90), from Falkirk, to M90 PERTH via A977. Take M90 & A90 to Forfar.
It is 321.80 miles according to MapQuest.
661.51 kilometres (411.04 miles)
The "as the crow flies" distance is 638.7 miles or 1,028 km.