Chain Rode Scope Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Standard anchoring geometry. Last verified 19 June 2026.

Anchoring safely means deploying enough rode for the scope ratio you want, measured from the bow roller to the seabed. That vertical distance is the charted depth plus the expected tidal rise plus the height of your bow above the water. Multiply it by your target scope to get the rode to let out. Enter your depth, tidal rise, bow height, and target scope to size the rode for high water.

Water depth now (feet or metres)

Expected tidal rise (same unit)

Bow roller height above water (same unit)

Target scope ratio (e.g. 5 for 5:1)

Vertical distance at high water

0.00

Rode to deploy

0.00

Scope formula

Vertical distance = water depth + tidal rise + bow height
Rode to deploy = scope ratio * vertical distance

Use the same length unit for all inputs. The rode result is in that same unit.

Worked example

Depth 15, tidal rise 6, bow height 4, target scope 5:1.
Vertical distance = 15 + 6 + 4 = 25.00.
Rode = 5 * 25 = 125.00 of chain or line.

Anchor scope: frequently asked questions

What is anchor scope?

Scope is the ratio of rode (chain or line) deployed to the vertical distance from the bow roller to the seabed. A common guide is 5:1 for all-chain rode and 7:1 for rope or rope-and-chain in settled conditions, increasing in stronger wind. Rode length = scope ratio * (water depth + tidal rise + bow height).

Why include bow height and tidal rise?

Scope is measured from the bow roller, not the waterline, so the bow height above the water adds to the vertical distance. Tidal rise must be added because the depth increases as the tide comes in, and the rode must still hold at high water. Ignoring these underestimates the rode needed.

Is more scope always better?

More scope lowers the angle of pull on the anchor, helping it hold, but it also increases the swinging circle. You need enough scope to hold safely without swinging into other boats or hazards. In a crowded anchorage you may use the minimum safe scope and watch the forecast.

Does chain hold better than rope at the same scope?

Yes. The weight of chain keeps the pull on the anchor more horizontal, so all-chain rode often holds at a lower scope (around 5:1) than rope (around 7:1 or more). This calculator lets you set whatever target scope suits your rode and conditions.

Official sources

U.S. Coast Guard: recreational boating safety, anchoring.
NOAA Office of Coast Survey: tides and water levels.

Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.