Thornthwaite Crag is a Lake District fell of 784 m in Westmorland and Furness. It rises only 30.6 m above its key col, 3.9% of its height.
Its drop of 30.6 m makes it a Hewitt but is short of the 150 m a Marilyn needs. The key col is close by, only 0.5 km to the east at 753.4 m. Its nearest higher summit, High Street, is also the hill its key col leads to. The highest point is recorded as rock 45m n of beacon and 10m e of wall, not a cairn.