Anchor Rode Length Calculator
Rode feet from depth, bow height, and scope.
What it does
Anchors hold when the pull runs nearly horizontal, and scope is what lays the pull flat. Too little line lifts the shank and the anchor strolls; enough line lets flukes dig to many times their weight.
The tool above takes water depth with bow height and the scope for conditions. It returns rode to pay out with the ratio and total vertical beside it, in feet or meters.
The defaults anchor in 10 ft with a 4 ft bow at 7 to 1: 14 ft total needing 98 ft of rode. The metric mirror (3.05 m, 1.22 m) needs 29.9 m.
The math follows BoatUS Foundation anchoring guidance with scope as rode over bow height above bottom: 7 to 1 recommended, 5 to 1 in calm, up to 10 to 1 in a blow. Northwest boat school tables work the same ratios to identical feet.
How to use
- Pick imperial (feet) or metric (meters).
- Enter water depth at high tide.
- Enter bow roller height above water.
- Pick calm, typical, or storm scope.
- Pay out the rode figure.
- Leave swing room around the full circle.
Formula
- depth
- Water under the keel at high tide.
- bow
- Waterline to bow roller height.
- scope
- Rode per unit of total vertical.
Depth alone understates scope on tall boats, so the bow term belongs in every figure. All chain rodes grip harder per foot, crowded anchorages trade scope for chain weight, and tide range adds straight to depth.
Worked example
Example: 10 ft depth, 4 ft bow, 7 to 1
Defaults: imperial, 10 ft water, 4 ft bow, typical 7 to 1.
- Total: 10 + 4 = 14 ft.
- Rode: 14 x 7 = 98 ft.
- Tool shows 98 ft rode, 7 to 1, 14 ft total.
- Calm 5 to 1 on the same spot: 70 ft.
- Storm 10 to 1: 140 ft.
- Metric mirror gives 29.9 m rode.
Reference table
| Scope | Rode | When |
|---|---|---|
| 5 to 1 | 70 ft | Calm, good holding |
| 7 to 1 | 98 ft | Typical overnight |
| 10 to 1 | 140 ft | Storm |
Limits
- Bottom type decides holding as much as scope.
- Swing room grows with every extra foot.
- Tide ebb strands short scope plans.
- Wind over 30 mph wants storm scope.
Common mistakes
- Scoping depth without bow height.
- Using low tide depth at anchor.
- Short scope in crowded anchorages.
- Forgetting swing room astern.
- Trusting scope without setting the hook.
Try it yourself
Quick checks. Answers sit tucked under each question.
12 ft with 3 ft bow at 5 to 1?
15 ft total needs 75 ft rode.
Same 14 ft at storm 10 to 1?
140 ft of rode.
Why add the bow?
Scope measures to the roller, not the waterline.
Questions
What is anchor scope?
Rode length over depth plus bow height; 7 to 1 is typical.
How much line for 10 ft of water?
With a 4 ft bow at 7 to 1, 98 ft of rode.
All chain different?
Chain grips flatter, so shorter scope holds; rope needs the full ratio.
Tide matters?
Yes, figure scope on high tide depth plus the full range.
Crowded anchorage?
Match neighbor scope or add chain; mixed scopes tangle swings.
Drag alarm set?
Set it past the swing circle, not at the drop point.