Anchor Scope Calculator

About this calculator

Scope is the ratio of anchor rode length let out to the total vertical distance from the seabed to the bow roller — that vertical distance being water depth plus bow height, not just depth alone. A common rule of thumb is 5:1 to 7:1 for all-chain rode in calm conditions and 7:1 to 10:1 for rope/chain combinations or heavier weather, since more scope flattens the pull angle on the anchor shank and lets it dig in and hold rather than dragging or breaking out.

The calculator takes water depth, bow roller height above the waterline, and your target scope ratio, and multiplies their sum by that ratio to give the rode length to deploy. Recreational boaters and sailors use it before setting anchor for the night to make sure they pay out enough rode to hold securely without over- or under-estimating by eye.