Anchor Rode & Scope Calculator
Calculate anchor rode length and scope ratio for chain or rope based on water depth and freeboard, free in your browser.
Enter Values
Minimum 0
How to use this calculator
- Enter the water depth and your scope ratio (e.g. 5:1 or 7:1).
- Optionally add the bow roller height above the water and extra tide to allow for.
- Read the length of rode to let out.
How it works
The Anchor Rode & Scope Calculator works out how much chain or rope to deploy so the anchor sets and holds. Scope is the ratio of rode length to the vertical height from the seabed to the bow roller.
Rode = scope × (water depth + bow roller height + tide allowance). A bigger scope lays the pull more horizontal so the anchor digs in rather than lifting out.
Worked example
5 m depth, 1 m bow height, 7:1 scope. Vertical height = 6 m, so rode = 7 × 6 = 42 m to deploy.
Frequently asked questions
What scope should I use?
As a rough guide: around 3:1 for a short lunch stop, 5:1 for normal conditions, and 7:1 or more for strong wind or overnight. All-chain rodes can use a little less than rope-and-chain.
Why include bow height and tide?
Scope is measured from the seabed to the bow roller, not just the water depth — so you add the height of the bow above the water, plus any rise of tide while you're anchored.
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Cite this tool
Zerdly. (2026). Anchor Rode & Scope Calculator. Retrieved from https://www.zerdly.com/tools/anchor-rode-scope-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.