Anchor & Mooring Calculator
Work out how much chain and rope to put out, and which anchor size your boat needs.
⚠️ These results are indicative and based on general rules of thumb for recreational boats. Always confirm against your vessel's documentation, the current conditions and local regulations.
A safe anchorage depends on the right scope (the ratio of rode length to depth) and on sizing the anchor, chain and mooring lines to your boat. Enter your data below and get the recommended values in seconds.
Result
- Total depth (water + freeboard)
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- Recommended scope
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- Minimum rode length
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- Recommended anchor weight
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- Recommended chain diameter
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- Recommended mooring line diameter
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Recommended products for safe anchoring
Self-Adjusting Anchor Buoy
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Bracket Anchor Stainless Steel AISI 316L
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Anchor Connector Stainless Steel
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Chain claw in stainless steel
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Stabilizer with bag
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Chainmarkers in colour
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Bracket Anchor galvanized - 14 Kg
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How this calculator works
The result combines two well-established rules used by sailors:
- Scope (rode vs. depth). The scope is how many times the water depth (plus the bow freeboard) you let out in chain and rope. Calm conditions need about 3:1, normal anchoring 5:1, rough weather 7:1 and storm conditions up to 10:1. Poor-holding bottoms (mud, rock or weed) need extra scope on top.
- Anchor, chain and line sizing. Anchor weight, chain diameter and mooring line diameter are recommended from the boat length (LOA). The figures below follow the common tables for monohull sailing and motor yachts.
Reference table: anchor, chain and mooring line by boat length
| Boat length (m) | Anchor weight | Chain diameter | Mooring line diameter |
|---|---|---|---|
| ≤ 5 | 6–8 kg | 6 mm | 10 mm |
| 5–7 | 10–12 kg | 6 mm | 12 mm |
| 7–9 | 12–16 kg | 8 mm | 12 mm |
| 9–11 | 16–20 kg | 8 mm | 14 mm |
| 11–13 | 20–25 kg | 10 mm | 16 mm |
| 13–15 | 25–32 kg | 10 mm | 16 mm |
| 15–18 | 32–40 kg | 12 mm | 18 mm |
| 18+ | 40–60 kg | 13 mm | 20 mm |
Frequently asked questions about anchoring
How much chain or rope should I let out when anchoring?
As a rule of thumb: 3 times the depth in calm conditions, 5 times for normal anchoring, 7 times in rough weather and up to 10 times in a storm. The depth to use is the water depth plus the height of your bow roller above the water.
Chain or rope rode — which is better?
Chain weighs down the anchor, resists chafing on the seabed and gives the best holding, so it is the first choice for the section next to the anchor. A mixed rode (chain plus rope) reduces weight and is common on smaller boats. In both cases the scope rules stay the same.
What anchor size do I need for my boat?
It depends mainly on the length and displacement of the boat, not on the number of anchors you carry. The reference table above gives a safe starting weight; for heavy-displacement boats or very exposed anchorages, go one size up.
How do I size my mooring lines?
Mooring line diameter grows with boat length and weight. The table above recommends a diameter that balances strength and ease of handling. As a general guide, the longer and heavier the boat, the thicker the lines.
How does the SWI-TEC automatic anchor buoy help with anchoring?
Our self-retracting anchor buoy marks the exact anchor position and shows other boats where your anchor lies, day and night. It is a simple, reliable safety aid for every anchorage.