Free Boat Anchor Size Calculator

Our boat anchor size calculator helps you estimate a practical primary anchor size using a manufacturer-style length and displacement method, then adjust it for wind, windage, and anchoring conditions.

Use overall length (LOA).
Use the boat's typical loaded displacement when possible.
This is a condition adjustment, not part of the base manufacturer-style table.
Enter the wind you are sizing for in knots (kt).
Used for guidance because holding capacity is anchor- and bottom-specific.

Your Anchor Size Estimate

Recommended primary anchor size
Base size
27 lb
Length + displacement
Condition size
33 lb
Wind + windage + use
Severe-weather size
44 lb
Planning step-up
Estimated wind load
0 lb
Not anchor holding capacity

Real-Boat Accuracy Check

We tested the calculator against real production sailboats using published boat length and displacement data. The comparison below shows the calculator's base recommendation alongside a reference anchor size from manufacturer sizing guidance.

Boat Length Displacement Calculator Reference Result
Catalina 30 29.9 ft 10,200 lb 27 lb 27 lb Exact
Hunter 33 32.7 ft 10,600 lb 27 lb 35 lb Close
Catalina 320 32.5 ft 11,300 lb 27 lb 35 lb Close
Pearson 34 33.8 ft 11,240 lb 33 lb 35 lb Very close
Catalina 36 36.3 ft 13,500 lb 33 lb 45 lb Difference
Tartan 37 37.3 ft 17,800 lb 44 lb 45 lb Very close
Catalina 380 38.4 ft 19,000 lb 44 lb 45 lb Very close
Morgan 38 38.4 ft 17,500 lb 44 lb 45 lb Very close
Bavaria 36 37.9 ft 11,817 lb 33 lb 45 lb Difference
Cal 40 39.3 ft 15,000 lb 55 lb 55 lb Exact
Island Packet 38 38.0 ft 21,500 lb 55 lb 55 lb Exact
Lagoon 380 37.9 ft 16,005 lb 55 lb* 55 lb Very close
Beneteau 393 38.2 ft 17,152 lb 44 lb 45 lb Very close
Catalina 350 35.4 ft 12,937 lb 33 lb 45 lb Difference
Hunter 36 35.9 ft 13,500 lb 33 lb 45 lb Difference
What does this test mean?

The calculator generally tracks the reference recommendations, with the largest differences occurring around the 33–36 ft range where different manufacturers move to heavier anchor sizes at different points. Anchor sizing is not standardized to one universal answer, so this table is a practical comparison rather than a guarantee of holding performance.

* Multihull adjustment applied. Reference sizes are intended as comparison benchmarks and may differ by anchor design, manufacturer, windage, anchoring conditions and bottom type.

How the Anchor Size Is Calculated

1. Base anchor size: length + loaded displacement

The base result uses a manufacturer-style two-dimensional sizing table. The calculator selects the smallest anchor size whose published-style limits cover both the vessel's length and loaded displacement. This avoids a single "pounds per foot" formula and avoids abrupt arbitrary displacement cutoffs.

Base size = smallest anchor size satisfying both
Boat length ≤ length limit AND displacement ≤ displacement limit

2. Weather and windage are separate adjustments

Wind speed is not converted directly into pounds of anchor. Wind load increases approximately with the square of wind speed, while anchor holding depends on anchor design, scope and seabed. Therefore the calculator uses wind and windage to determine whether to step up to the next practical anchor size.

Wind force ≈ 0.0053 × CD × A × V²

3. Multihulls and high-windage boats

Multihulls and unusually high-windage boats can create greater loads than a typical monohull. The calculator therefore moves up the practical anchor-size scale instead of trying to invent a universal mathematical holding multiplier.

4. Severe-weather result

The severe-weather result is a planning step-up from the base recommendation. It is not a prediction of the exact anchor that will hold in a storm. For a specific anchor model, the manufacturer's current sizing recommendation should take precedence.

5. Bottom type

Bottom type is shown as a warning because the same anchor can perform very differently in sand, mud, grass or rock. There is no defensible universal "mud = X% more anchor" factor that applies to all anchor designs.

This calculator is an estimate and is not a substitute for the current sizing chart and instructions from the manufacturer of the specific anchor you plan to use.