Minimum HDD Length

Every HDD has a geometric minimum length: the shortest surface-to-surface bore that can dive to the required depth of cover, level off, and climb back out without violating the minimum bend radius. This calculator returns that minimum length from the entry and exit angles, target depth, and allowable radius.

It is the first geometry check when laying out a crossing — if the available right-of-way is shorter than this, the profile is not feasible as drawn.