Mooring Line Length Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Mooring Line Length Calculator
Not sure what length dockline to buy? This calculator applies common sizing guidelines based on boat length and line type.
Common Sizing Guidelines
| Line Type | Recommended Length |
|---|---|
| Bow/Stern Line | ~2/3 of boat length |
| Spring Line | ~Equal to boat length |
| Breast Line | ~1/3 of boat length |
Example
A 30 ft boat's spring line:
Recommended Length = 30 x 1.0 = 30 ft
What Each Line Type Does
Spring lines resist forward/backward movement at the dock (they run diagonally, forward or aft, from a midship or bow/stern cleat), bow and stern lines hold the boat's ends in position, and breast lines are short lines running perpendicular to the dock that hold the boat directly against it.
These Are Starting Points, Not Fixed Rules
Actual required length also depends on dock configuration, tidal range at the specific location (a location with large tidal swings needs longer lines to accommodate the boat rising and falling with the tide without going taut or slack), and expected weather/wake conditions - always adjust these guidelines to your specific dock and location.