Anchor Size Chart: Pick the Right Anchor for Your Boat

What does a 22-pound anchor for a 40-foot boat mean?

On the default — a 40-foot boat — the anchor weight is 22 lb = 9.98 kg and the class is a medium anchor. The anchor weight is the weight of the anchor itself, and 22 lb is the standard anchor for a 40-ft boat — the general-purpose cruising anchor, heavy enough to hold in a blow without needing a windlass the way a 35-lb anchor does. The kilograms are the pounds times 0.45359237: 22 × 0.45359237 = 9.98 kg. The classes are CLOSED at both ends: small 15–25 ft, medium 30–45 ft, large 50–70 ft (boat LENGTH). Lengths between the classes (26–29 ft and 46–49 ft) match NO standard class — the classes have gaps, they are not continuous — and lengths of 71 ft and above, and below 15 ft, match NO standard class either.

Three things about the model are worth stating plainly.

First, the conversion is 22 × 0.45359237 = 9.98 kg. Second, the meaning is a 22-pound anchor for a 40-foot boat — the general-purpose cruising anchor, heavy enough to hold in a blow without needing a windlass. And third, the kilogram figure is displayed to two decimals, half-up, and a figure that displays as 9.98 kg can sit a hair below the line — 40 ft gives 9.9790 kg, which displays as 9.98 kg — and one that displays as 6.35 kg can sit a hair below it — 30 ft gives 6.3503 kg, which displays as 6.35 kg. The page prints the unrounded value so the rounding does not mislead you.

The worked example, line by line

Setup: boat 40 feet long.

Line 1 — the anchor weight. A 40-foot boat takes a 22-lb anchor.

Line 2 — the kilograms. 22 × 0.45359237 = 9.98 kg (unrounded 9.9790 kg).

Line 3 — the class. 40 feet sits in the middle of the 30–45 ft medium class, so the class is a medium anchor.

Line 4 — the check. At the 45-ft row the anchor is 29 lb = 13.15 kg, above 10.00 kg; and at the 40-ft row it is 22 lb = 9.98 kg — below 10.00 kg.

Every boat length in the table, checked

The table runs from 15 to 70 feet. Every length in the table sits inside one of the three classes: 15–25 ft are small boats, 30–45 ft are medium boats and 50–70 ft are large boats. The classes are closed at both ends — 25 ft is a small boat, 45 ft is a medium boat and 70 ft is a large boat. Lengths between the classes (26–29 ft and 46–49 ft) match NO standard class, and lengths of 71 ft and above, and below 15 ft, match NO standard class either. The table is a synthesis of published anchor-sizing guidance for moderate conditions and average windage — a 22-lb anchor for a 35–42 ft boat is the published standard, and the weight roughly doubles as boat length grows. Sizing varies by anchor type (a lightweight fluke anchor runs about half the weight of a plow), bottom, and wind — size up one row in exposed anchorages or storm conditions, and always check the anchor maker's own table for the exact model.

15 ft: 15 ft = 5 lb = 2.27 kg; small anchor — 15 feet is the bottom of the table, a small anchor.

20 ft: 20 ft = 8 lb = 3.63 kg; small anchor — 20 feet is a small anchor, five feet above the bottom of the table.

25 ft: 25 ft = 11 lb = 4.99 kg; small anchor — 25 feet is a small anchor, the top of the small class.

30 ft: 30 ft = 14 lb = 6.35 kg; medium anchor — 30 feet is a medium anchor, the bottom of the medium class.

40 ft: 40 ft = 22 lb = 9.98 kg; medium anchor — 40 feet is a medium anchor, the middle of the medium class.

50 ft: 50 ft = 35 lb = 15.88 kg; large anchor — 50 feet is a large anchor, the bottom of the large class.

Length bars — 15 ft, 40 ft, 70 ft: 15 ft: 5 lb = 2.27 kg — small anchor; 40 ft: 22 lb = 9.98 kg — medium anchor; 70 ft: 77 lb = 34.93 kg — large anchor — one length from each class: the bottom of the table, the classic cruising-boat anchor and the top of the table.

The reverses, worked backwards

Smallest table row whose anchor reaches 10.00 kg: At the displayed 45 ft row the figures are 45.00 ft = 29 lb = 13.15 kg (unrounded 13.1542 kg); medium anchor. At the 40-ft row the anchor is 22 lb = 9.98 kg (unrounded 9.9790 kg), below 10.00 kg — so the 45-ft row is the smallest table row whose anchor reaches 10.00 kg.

Largest table row whose anchor STAYS at or below 10.00 kg: At the displayed 40 ft row the figures are 40.00 ft = 22 lb = 9.98 kg (unrounded 9.9790 kg); medium anchor. At the 45-ft row the anchor is 29 lb = 13.15 kg (unrounded 13.1542 kg), above 10.00 kg — so the 40-ft row is the largest table row whose anchor stays at or below 10.00 kg.

Smallest table row that needs a medium anchor: At the displayed 30 ft row the figures are 30.00 ft = 14 lb = 6.35 kg (unrounded 6.3503 kg); medium anchor. At the 25-ft row the anchor is 11 lb = 4.99 kg, a small anchor — so the 30-ft row is the smallest table row that needs a medium anchor.

Smallest table row whose anchor reaches 20.00 kg: At the displayed 60 ft row the figures are 60.00 ft = 55 lb = 24.95 kg (unrounded 24.9476 kg); large anchor. At the 55-ft row the anchor is 44 lb = 19.96 kg (unrounded 19.9581 kg), below 20.00 kg — so the 60-ft row is the smallest table row whose anchor reaches 20.00 kg.

Largest table row whose anchor STAYS at or below 25.00 kg: At the displayed 60 ft row the figures are 60.00 ft = 55 lb = 24.95 kg (unrounded 24.9476 kg); large anchor. At the 65-ft row the anchor is 66 lb = 29.94 kg (unrounded 29.9371 kg), above 25.00 kg — so the 60-ft row is the largest table row whose anchor stays at or below 25.00 kg.

Smallest table row that needs a large anchor: At the displayed 50 ft row the figures are 50.00 ft = 35 lb = 15.88 kg (unrounded 15.8757 kg); large anchor. At the 45-ft row the anchor is 29 lb = 13.15 kg (unrounded 13.1542 kg), a medium anchor — so the 50-ft row is the smallest table row that needs a large anchor.

A warning about the neighbours: every neighbour above sits one table row from the star, and every neighbour kilogram figure is a hair below or above the target even though it displays as the target — a one-row move changes the kilograms by more than a kilo, but the unrounded figure still sits a hair from the round displayed figure, so the displayed two-decimal figure cannot tell the star from its neighbour. The page prints the unrounded four-decimal value in full so the rounding does not mislead you: 13.1542, 9.9790, 24.9476, 19.9581, 29.9371, 15.8757, 6.3503, 8.1647, 2.2680, 34.9266.

What the defaults assume

The defaults are a boat 40 feet long — 40 ft = 22 lb = 9.98 kg; medium anchor. With 15 ft, 15 ft = 5 lb = 2.27 kg; small anchor. With 20 ft, 20 ft = 8 lb = 3.63 kg; small anchor. With 25 ft, 25 ft = 11 lb = 4.99 kg; small anchor. With 30 ft, 30 ft = 14 lb = 6.35 kg; medium anchor. With 40 ft, 40 ft = 22 lb = 9.98 kg; medium anchor. With 50 ft, 50 ft = 35 lb = 15.88 kg; large anchor. With Length bars — 15 ft, 40 ft, 70 ft, 15 ft: 5 lb = 2.27 kg — small anchor; 40 ft: 22 lb = 9.98 kg — medium anchor; 70 ft: 77 lb = 34.93 kg — large anchor. With Length 0 ft, 0 ft = no anchor weight = 0.00 kg; matches no standard class — no length at all, and no matching class. With Length -5 ft, 0 ft = no anchor weight = 0.00 kg; matches no standard class — a negative length is floored to 0.00 kg, never a negative number. With Length 40 ft, 40 ft = 22 lb = 9.98 kg (unrounded 9.9790 kg); medium anchor — the kilogram figure displays as 9.98 kg. With Length 30 ft, 30 ft = 14 lb = 6.35 kg (unrounded 6.3503 kg); medium anchor — the kilogram figure displays as 6.35 kg. With Length 70 ft, 70 ft = 77 lb = 34.93 kg; large anchor — the top of the table. With Length 27 ft, 27 ft = 14 lb = 6.35 kg; matches no standard class — in the gap between the small and medium classes, so no standard class. With Length 47 ft, 47 ft = 35 lb = 15.88 kg; matches no standard class — in the gap between the medium and large classes, so no standard class. With Lengths 15, 25, 30, 45, 50, 70, 75 and 10 ft, 15 ft = 5 lb = 2.27 kg — small anchor; 25 ft = 11 lb = 4.99 kg — small anchor; 30 ft = 14 lb = 6.35 kg — medium anchor; 45 ft = 29 lb = 13.15 kg — medium anchor; 50 ft = 35 lb = 15.88 kg — large anchor; 70 ft = 77 lb = 34.93 kg — large anchor; 75 ft = 77 lb = 34.93 kg — matches no standard class; 10 ft = 5 lb = 2.27 kg — matches no standard class — the bottom of the small class, the top of the small class, the bottom of the medium class, the top of the medium class, the bottom of the large class, the top of the large class, past the large class, and below the small class. With Length 55 ft, 55 ft = 44 lb = 19.96 kg (unrounded 19.9581 kg); large anchor — the kilogram figure displays as 19.96 kg. With Length 35 ft, 35 ft = 18 lb = 8.16 kg (unrounded 8.1647 kg); medium anchor — inside the medium class. With Length 12 ft, 12 ft = 5 lb = 2.27 kg (unrounded 2.2680 kg); matches no standard class — below the 15-ft small class, so no standard class.

A note on the rounding: the kilogram figure is displayed to two decimals, half-up. With a 40-ft boat the unrounded figure is 9.9790 kg — it displays as 9.98 kg. With a 30-ft boat the unrounded figure is 6.3503 kg — it displays as 6.35 kg. With a 55-ft boat the unrounded figure is 19.9581 kg — it displays as 19.96 kg. With a 35-ft boat the unrounded figure is 8.1647 kg — it displays as 8.16 kg. With a 12-ft boat the unrounded figure is 2.2680 kg — it displays as 2.27 kg. The page prints the unrounded value so the rounding does not mislead you.

Output · formula · meaning

Who uses this

• The cruiser buying a new anchor: they learn a 40-foot boat needs a 22-pound anchor — 9.98 kg, a medium anchor — and they check the 45-ft row to see the smallest row whose anchor reaches 10.00 kg.
• The daysailer sizing a small-boat anchor: they learn the small class is 15–25 ft and below 14 lb the anchor is a day anchor that drags in any real wind — and they check the 30-ft row to see the smallest row that needs a medium anchor.
• The liveaboard fitting a windlass: they learn above 29 lb the anchor needs a windlass and heavier ground tackle — and they check the 60-ft row to see the smallest row whose anchor reaches 20.00 kg.
• The student converting pounds to kilograms: they learn the kilograms are the pounds times 0.45359237 — and they check the 50-ft row to see the smallest row that needs a large anchor.

Accuracy & limitations

The math is first-principles: the kilograms are the anchor weight in pounds times 0.45359237, and the class comes from the closed bands — small 15–25 ft, medium 30–45 ft, large 50–70 ft (boat LENGTH) — all in feet, pounds and kilograms, the kilogram figure displayed to two decimals half-up. There is no division in this calculator — nothing is ever undefined. A negative length is floored to 0.00 kg, never a negative number. With a 40-ft boat the unrounded figure is 9.9790 kg — it displays as 9.98 kg. With a 30-ft boat the unrounded figure is 6.3503 kg — it displays as 6.35 kg. With a 55-ft boat the unrounded figure is 19.9581 kg — it displays as 19.96 kg. 22 lb is the standard anchor for a 40-ft boat — the general-purpose cruising anchor, heavy enough to hold in a blow without needing a windlass the way a 35-lb anchor does; below 14 lb the anchor is a day anchor for small boats that drags in any real wind; above 29 lb the anchor needs a windlass and heavier ground tackle. 15 ft is the small floor — below it a dinghy anchor does the job; 70 ft is the practical ceiling — above it the anchor is a ship's job, sized by classification rules, not a chart. This is why the medium zone runs 30–45 ft while the small zone stops at 25 ft — the medium anchor is the cruising boat's anchor, and 40 ft is its middle. What the model cannot do is pick the anchor for you: it says nothing about the anchor type, the bottom or the wind — a 22-lb anchor that holds in mud can drag on rock, and a lightweight fluke anchor runs about half the weight of a plow. Size up one row in exposed anchorages or storm conditions, and always check the anchor maker's own table for the exact model. Use it to check the size before you buy — then check the anchor-bolt, chain, screw-length and bolt-size charts before you set the rest of the ground tackle.

No anchor-size page of any kind exists on the site — this is the first. The closest page is the anchor-bolt size chart (anchor BOLTS — the threaded fasteners that hold a bracket to concrete, not boat anchors). This one is the BOAT anchor's own 12-row boat-length → anchor-weight reference (15–70 ft, pounds and kilograms) with its three boat-size classes (small 15–25 ft, medium 30–45 ft, large 50–70 ft) and class/gap logic.

Frequently asked questions