Anchor Chain Length Calculator

Work out anchor chain length instantly with clear inputs, formula shown and shareable results.

About Anchor Chain Length Calculator

Scope is measured from the bow roller, not the waterline, so bow height must be added to the depth. Five to one is the normal minimum for chain, seven for strong wind and ten in a storm; rope needs 50% more because it lacks the catenary weight that keeps the pull horizontal.

Formula

Anchor scope

rode length = (depth + bow height) x scope ratio; chain 5:1 normal, rope 7.5:1

Worked example

With the default values below, Anchor Chain Length Calculator returns Rode to deploy of 37.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Water depth: 6 m
Bow height above water: 1.4 m
Conditionsone of Calm, short stay, Moderate, Strong wind, Storm: Moderate
Rode typeone of All chain, Chain and rope, All rope: All chain

Results

Rode to deploy: 37.00 m
Scope ratio: 5.00 :1
Total vertical drop: 7.40 m
Holding note: Chain catenary keeps the pull horizontal at the anchor

Step by step

1Values used
2Anchor scope
3Rode to deploy= 37.00 m
4Scope ratio= 5.00 :1
5Total vertical drop= 7.40 m
6Holding note= Chain catenary keeps the pull horizontal at the anchor

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does rope need more scope?

Chain's weight forms a catenary curve that keeps the pull at the anchor shank horizontal. Rope floats up under load, lifting the shank and reducing holding power.

Should I allow for tidal range?

Yes, always calculate on high water depth. Anchoring on a rising tide with minimum scope is a classic way to drag at 3 am.