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Free tool · Sailboat anchoring

What size anchor does your boat need, and how much rode?

Two answers every cruiser wants: the right anchor size for your boat and the rode to deploy when you swing on the hook. Enter your length and anchor type for a manufacturer-chart range plus the cruising size-up, then size your scope from depth, freeboard, and conditions. A planning guide to get you in the right range, not a guarantee that any anchor will hold, so always confirm with your anchor maker's chart and size up when in doubt.

Read first: this is a planning guide based on manufacturer and ABYC sizing practice, not a guarantee that a given anchor will hold your boat. Holding depends on the anchor's design, the bottom, your boat's windage, and how you set it, and a dragging anchor is a safety event. Treat the chart as a minimum, lean toward sizing up, and confirm against your chosen anchor manufacturer's own chart before you buy.

1 · Anchor size

2 · Scope & rode

A planning guide using accepted manufacturer and ABYC sizing practice. Confirm the anchor against your maker's chart, and remember the chart is a minimum.

How to size an anchor and its scope

The calculator above is just this six-step method. You can run it by hand.

Step 1: Size the anchor by length, then by type

Manufacturers size a primary anchor by boat length, adjusted for displacement and windage (Mantus and others derive their charts from ABYC load tables, roughly 900 lb of load for a 35 ft boat in 30 knots). But the weight on the chart only means something once you fix the anchor TYPE: a new-generation scoop (Rocna, Mantus, Vulcan, Spade) holds far more per pound than an old plow or claw, and an aluminium fluke (Fortress) sizes lighter still for the same hold. So the right answer is a weight range for your type, not one number.

Step 2: Treat the chart as a floor, and size up

Every authoritative source (West Marine, Practical Sailor, the makers' own 50-knot assumptions) treats the manufacturer chart as a minimum for average conditions and an average bottom. For a cruising boat that anchors out and sleeps aboard, the standard advice is to go one size up from the chart into the heavier column. Oversizing the bower is cheap insurance; an anchor that drags at 2 a.m. is not.

Step 3: Set the scope from effective depth, not gauge depth

Scope is the ratio of rode deployed to the height from the seabed to your bow roller. Rode to let out = (water depth at high tide + height of your bow roller above the water + the tidal range you will swing through) x the scope ratio. People drag because they scope off the depth sounder reading and forget the freeboard and the rising tide.

Step 4: Pick the scope ratio for the conditions and rode

Treat 3:1 as a deep-water or emergency minimum only, never as an overnight scope. For an attended lunch hook in a flat calm, 4:1 all-chain is the floor; never anchor overnight below 5:1 all-chain, and 7:1 is the standard working scope you want as the wind builds, rising to 10:1 in a blow or when you leave the boat. A rope-and-chain rode needs more than all-chain (say 7:1 overnight, 8 to 10:1 in a blow) because it lacks the chain's weight.

Step 5: Do not over-credit all-chain catenary

An all-chain rode sags into a curve (catenary) that lowers the pull angle, which is why all-chain can hold at a shorter scope than rope in light air. But that curve straightens as the wind rises, and above about 25 knots the advantage is largely gone, so treat the lower all-chain ratio as a calm-water allowance, not a shortcut: when it blows, pay out more. An all-chain rode also needs a nylon snubber or bridle to absorb the shock loads, both to protect the gear and because ABYC is explicit that the windlass is not a strong point to anchor from.

Step 6: Set it, snub it, and read the bottom

Sizing is only half the job. A correctly sized anchor that is dropped and left will drag, so back down firmly under power to set it and watch a transit or your GPS to confirm it has bitten. Holding swings by an order of magnitude with the bottom: check the chart and your sounder, because a fluke anchor in grass, kelp, rock, or soft mud can hold almost nothing. Mind your swing circle too, roughly twice the rode length plus your boat length, which matters in a crowded anchorage. This tool sizes a primary bower for normal cruising; storm, offshore, and unattended anchoring need a second anchor, more rode, and dedicated storm tactics, not a sizing calculator.

Anchor size chart, by boat length

Working-anchor weight for a new-generation steel scoop, the convergent manufacturer-chart baseline (Rocna and Mantus class, derived from ABYC windage loads). It is a minimum for average conditions: a plow sizes similarly, a claw should go up a size, and an aluminium fluke sizes lighter for the same hold. A cruising boat should step up one row.

Boat length Scoop, pounds Metric
Up to 20 ft 9 to 15 lb 4 to 7 kg
20 to 26 ft 15 to 22 lb 7 to 10 kg
26 to 31 ft 22 to 33 lb 10 to 15 kg
31 to 36 ft 33 to 44 lb 15 to 20 kg
36 to 41 ft 44 to 55 lb 20 to 25 kg
41 to 46 ft 55 to 73 lb 25 to 33 kg
46 to 51 ft 73 to 88 lb 33 to 40 kg
51 to 61 ft 88 to 121 lb 40 to 55 kg
61 ft and up 121 to 154 lb 55 to 70 kg

Once you have your numbers, here is the ground tackle

Size first with the tool, then shop the anchor, chain, and windlass with these.

How we are paid: some links above go to Amazon, and if you buy through them we earn a commission at no extra cost to you. It does not change what we recommend. For the whole picture, see our complete boat gear guide.

Common questions

What size anchor do I need for my boat?

Size by boat length first, then by anchor type. As a manufacturer-chart baseline, a new-generation steel scoop (Rocna, Mantus, Vulcan) runs about 9 to 15 lb for a boat up to 20 ft, 22 to 33 lb at 30 ft, 33 to 44 lb at 35 ft, and 55 lb or more by 45 ft. A plow sizes similarly; a claw should go up a size; an aluminium fluke (Fortress) sizes lighter for the same hold. The chart is a minimum, so a cruising boat should go one size up, and you should always verify against your specific anchor maker's chart because holding per pound varies widely.

What is the right anchor scope ratio?

Scope is rode length divided by the height from the seabed to your bow roller. Treat 3:1 as a deep-water or emergency minimum only, never as an overnight scope. 4:1 all-chain works for an attended lunch hook in a flat calm; never anchor overnight below 5:1 all-chain; 7:1 is the standard working scope you want as the wind builds; and 10:1 is for storm conditions or when you leave the boat. A rope-and-chain rode needs more scope than all-chain because it has no chain weight to lower the pull angle.

How much anchor rode should I let out?

Take the water depth at high tide, add the height of your bow roller above the water, add the tidal range you will swing through, and multiply that total by your scope ratio. For example, 15 ft of water plus a 4 ft bow roller plus a 3 ft tide is 22 ft of effective depth; at a 5:1 overnight scope that is 110 ft of rode. The most common reason boats drag is scoping off the depth sounder and forgetting the freeboard and the tide.

Does anchor type change the size I need?

Yes, a lot. Modern scoop anchors (Rocna, Mantus, Spade, Vulcan) hold far more per pound than older plow (CQR, Delta) or claw (Bruce) designs, and an aluminium fluke (Fortress) holds more per pound still in the right bottom but less in others. That is why a sizing answer has to be a weight for a named type, not a bare number: West Marine notes modern anchors can hold 10 to 200 times their own weight depending on design and bottom.

What size chain do I need for my anchor?

As a rule of thumb, marine sources suggest roughly 1/8 inch of chain diameter for every 8 to 10 ft of boat, adjusted up for high windage; a high-tensile grade (G4 or HT) lets you carry a smaller, lighter diameter for the same strength, while older BBB proof coil often needs the next size up. Carry enough of it: an all-chain cruising rode usually wants 200 to 300 ft so you can reach 7:1 in a typical anchorage, and a rope-and-chain rode wants at least one to one and a half boat lengths of chain at the anchor end. The catch is that your windlass gypsy must match the chain's grade and pitch exactly: 5/16 inch G4 is not interchangeable with 5/16 inch BBB. See our anchor chain guide for the detail.

Does this replace my anchor maker's sizing chart?

No. This is a planning guide to get you in the right range and help you shop, not a guarantee that any particular anchor will hold your boat. Holding depends on anchor design, bottom type, your boat's windage, and how you set it, and a dragging anchor is a safety event. Always confirm against your chosen anchor manufacturer's own sizing chart for your boat, and when in doubt, size up.

Disclaimer

This calculator and page are provided for general informational and educational purposes only and reflect accepted manufacturer and ABYC anchor-sizing practice as of 2026. They are not a guarantee that any anchor, size, or scope will hold a particular boat in any condition. Anchor holding depends on the anchor's design, the seabed, your boat's windage and displacement, the rode, and how the anchor is set, all of which vary. A dragging anchor can cause loss of the vessel, injury, or death. We make no warranty, express or implied, as to accuracy, completeness, or fitness for any particular boat. You alone are responsible for selecting, sizing, and setting your ground tackle, and Sorted Gear accepts no liability for any loss, injury, or damage arising from reliance on this information. An all-chain rode requires a nylon snubber or bridle, because the windlass is not an anchoring strong point, and holding assumes firm sand or mud, a properly set anchor, and a monohull; rocky, weedy, or soft bottoms, an unset anchor, or a catamaran or other high-windage vessel may need a larger anchor or a different type. This is not a guide for storm anchoring, offshore use, or any condition where a dragging anchor threatens life. Always confirm against your anchor manufacturer's own sizing chart, size up when in doubt, and seek qualified advice for offshore or storm use. Last reviewed June 2026.

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