Anchor Line Length by Depth

Free guide

How much anchor line do you need?

How much line to let out for any depth. Why you add your bow height first. Which tide to plan for. Plus a calculator that does the math for you.

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Side view of an anchored boat: rope runs from the bow roller down to chain on the bottom and a dug-in anchor, with depth and bow height marked

5 anchoring questions, answered

Guess first, then tap for the answer.

10 ft of water and a 3 ft bow: how much line?
10 ft of water, 3 ft bow: how much line?
Tap for the answer

Add them first: 10 + 3 = 13 ft. At 5:1 that is 65 ft of rode. At 7:1 it is 91 ft. Chain and rope count together. More below

Gear for this step

Boat Anchor KitBoat Anchor KitA fluke style anchor, chain, shackles and rope sold as a set, sized by boat lengthView productSee current price at betterboat.com
Why add your bow height to the depth?
Why add your bow height to the depth?
Tap for the answer

Scope is measured from the bow roller down to the bottom, not from the waterline. Every extra foot of bow height adds 5 ft of rode at 5:1 and 7 ft at 7:1. More below

Gear for this step

Boat Anchor SwivelBoat Anchor SwivelA rotating 316 stainless steel swivel that fits between anchor and chain, for setups that run over a bow...View productSee current price at betterboat.com
High tide or low tide: which depth do you use?
High tide or low tide: which depth do you use?
Tap for the answer

The greatest depth you expect during your stay, even if the tide is falling when you arrive. Then make sure you still have water under the boat at low tide. More below

Gear for this step

Boat Anchor KitBoat Anchor KitA fluke style anchor, chain, shackles and rope sold as a set, sized by boat lengthView productSee current price at betterboat.com
Is 100 ft of anchor line enough?
Is 100 ft of anchor line enough?
Tap for the answer

With a 3 ft bow, 100 ft covers 15 ft of water at 5:1 and 10 ft of water at 7:1. Deeper than that, or 7:1 in 15 ft or more, needs a longer rode. BoatUS recommends carrying extra line. More below

Gear for this step

Boat Anchor LinesBoat Anchor Lines100 ft of 3/8 inch double braided nylon anchor line with a pre spliced stainless thimbleView productSee current price at betterboat.com
More line means a bigger swing circle around the anchor
Let out more line. What else changes?
Tap for the answer

Your swing circle. The boat swings around the anchor as wind and current shift, so more rode means a bigger circle. Check the whole area for other boats, shoals and anything in the way. More below

Gear for this step

Box Anchor for Boats Folding AnchorBox Anchor for Boats Folding AnchorA folding box anchor with a double sided design that stores flat, in 13, 19 and 26 lb sizesView productSee current price at betterboat.com

Jump to a topic

(Water depth + bow roller height) × scope = rode to let out
Example: 15 ft of water + 3 ft bow height = 18 ft. At 5:1, that's 18 × 5 = 90 ft of rode.

Scope is the ratio of rode to the vertical distance from your bow roller down to the bottom. Use water depth measured from the waterline to the bottom. Check whether your sounder displays depth below the transducer, below the keel or below the waterline, and correct it before adding bow height.

Use the greatest water depth expected during your stay, even if the tide is falling when you arrive. Also check clearance beneath the boat at low water.

Your depth, your boat

5:1 scope
 
7:1 scope
 
10:1 scope
 

Enter a depth. Results are rounded up to the next whole foot and count chain plus rope.

The chart

Between rows, round up to the next depth. Outside this range, use the formula or the calculator above.

Rode to let out with a bow roller 3 ft above the waterline
Water depth Depth + 3 ft bowvertical distance 5:1 scope 7:1 scope
5 ft 8 ft 40 ft 56 ft
10 ft 13 ft 65 ft 91 ft
15 ft 18 ft 90 ft 126 ft
20 ft 23 ft 115 ft 161 ft
25 ft 28 ft 140 ft 196 ft
30 ft 33 ft 165 ft 231 ft
35 ft 38 ft 190 ft 266 ft
40 ft 43 ft 215 ft 301 ft
45 ft 48 ft 240 ft 336 ft
50 ft 53 ft 265 ft 371 ft

Measure your own bow height: each extra foot adds 5 ft of rode at 5:1 and 7 ft at 7:1.

Picking a scope

5:1 may suit short, attended anchoring in calm, sheltered conditions with suitable gear and good holding ground. BoatUS describes a shorter 5:1 scope as acceptable for a lightweight anchor on a small boat in good conditions.

7:1 is the general recommendation from BoatUS and Discover Boating for rope and chain rode, subject to your anchor manufacturer's instructions.

10:1 is what Better Boat's anchoring guide suggests for stormy conditions, which is 530 ft in 50 ft of water with a 3 ft bow. More scope may help when conditions worsen, but no ratio makes holding certain. Reassess shelter, bottom, gear and swing room. Relocate before conditions become unsafe.

Gear for this step

Boat Anchor ChainBoat Anchor ChainA galvanized or stainless steel chain section with connection shackles, in 3/16, 1/4 and 5/16 inch sizesView productSee current price at betterboat.com
Scope alone doesn't mean you'll hold.
  • Bottom type matters. A fluke anchor does well in sand or mud and poorly on rock, according to Discover Boating.
  • The anchor has to suit your boat's size, and it has to actually set. Let the wind or current carry you back (or back down slowly) as the rode pays out.
  • Secure the rode to a suitable bow strong point. Set and verify the anchor holds, then monitor position. Check the full swing area for boats, shoals and obstructions.
  • Weather changes. BoatUS advises letting out more rode as the wind builds.
  • More rode means a bigger circle around the anchor, so make sure you have the room for it.

Gear for this step

Fluke Anchor with Slip RingFluke Anchor with Slip RingA galvanized fluke anchor, the type Discover Boating pairs with sand and mudView productSee current price at betterboat.com

Is your rode long enough?

On this chart, 100 ft of deployed rode covers the 15-ft row at 5:1 and the 10-ft row at 7:1. Count deployed chain plus rope. Allow for line needed aboard. Deeper water, or 7:1 in 15 ft or more, needs a longer rode; BoatUS recommends carrying extra line.

Gear for this step

Boat Anchor LinesBoat Anchor Lines100 ft of 3/8 inch double braided nylon with a pre spliced stainless thimble and a reflective strand...Check fit on the product pageView productSee current price at betterboat.com

Gear for this job

Boat Anchor KitBoat Anchor KitA fluke style anchor with chain, shackles and rope, sized by boat lengthView productSee current price at betterboat.comBoat Anchor LinesBoat Anchor Lines100 ft of 3/8 inch double braided nylon anchor line with a pre spliced stainless thimbleView productSee current price at betterboat.comBoat Anchor ChainBoat Anchor ChainA short chain section (4 or 5 ft by size) with connection shackles.Check fit on the product pageView productSee current price at betterboat.comBoat Anchor SwivelBoat Anchor SwivelA 316 stainless steel swivel that fits between anchor and chainView productSee current price at betterboat.comStainless Steel Bow ShacklesStainless Steel Bow ShacklesFour 316 stainless screw pin shackles for connecting chain, anchor and lineView productSee current price at betterboat.comBungee Anchor LineBungee Anchor LineA stretch anchor line for small boats, PWC and kayaks.View productSee current price at betterboat.comFluke Anchor with Slip RingFluke Anchor with Slip RingA galvanized fluke anchor, the type Discover Boating pairs with sand and mudView productSee current price at betterboat.comBox Anchor for Boats Folding AnchorBox Anchor for Boats Folding AnchorA folding box anchor that stores flat; its product page lists mud and rock bottomsView productSee current price at betterboat.comRiver Anchor for BoatsRiver Anchor for BoatsA vinyl coated mushroom and fluke style anchor for small boats in rivers and lakesView productSee current price at betterboat.comBoat Anchor BuoysBoat Anchor BuoysAn inflatable buoy kit for anchor retrievalView productSee current price at betterboat.comHot Knife Rope CutterHot Knife Rope CutterA heated blade that cuts and seals synthetic rope endsView productSee current price at betterboat.com

Sources and manufacturer instructions

This chart is a starting point only. Conditions, anchor type and bottom all change the answer. Count chain and rope together when you measure. Better Boat