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Hook sizing

Explainer · Last reviewed 2026-08-11

Hook sizes run on two scales that meet in the middle and neither is standardised between makers, which is why the same number can arrive as two different hooks.

Hook numbering is two systems stitched together, and knowing that is most of what makes it legible.

Below a certain size, hooks are numbered and the number gets LARGER as the hook gets SMALLER: a size 20 is tiny, a size 10 is bigger, a size 2 bigger still. Above that point the scale flips into the aught sizes, written 1/0, 2/0, 3/0 and read as "one-oh", and there the number gets larger as the hook does. A 6/0 is a large hook. The two scales meet between size 1 and 1/0, which are adjacent sizes with no gap between them despite looking like the beginning of two different sequences.

What the number describes is, loosely, the gape — the distance between the point and the shank. It does not describe wire diameter, shank length, point style or the weight of fish the hook will hold, and this is the source of most confusion. A size 4 fine-wire hook for freshwater and a size 4 forged sea hook are the same size and completely different objects.

There is no international standard behind either scale. Sizes are maker conventions that have drifted towards rough agreement without ever arriving, so a size 6 from one factory can sit visibly beside a size 6 from another and be a size out. Anglers who move between brands learn this by holding hooks up against each other, which remains the only reliable method.

Which dimensions actually change the hook's behaviour

Gape decides what the hook can get around. A bait that fills the gape leaves nothing for the point to catch on, and a hook whose gape is wider than the fish's jaw thickness cannot rotate into a hold. Both failure modes are common and both look like bad luck.

Wire diameter decides two opposing things at once. Fine wire penetrates with less force and does less damage, and it opens out under sustained load. Heavy forged wire holds against a large fish and needs more force to set, which is why heavy-wire patterns are usually paired with lower-stretch line and firmer rods. Choosing wire is choosing which of those two problems you would rather have.

Shank length changes leverage and how the hook sits in a bait. A long shank gives a hooked fish more mechanical advantage to lever against, and gives an angler more to grip when unhooking; a short shank reduces leverage and is harder to remove. Neither is a general improvement.

The eye — turned up, turned down or straight — changes how the hook aligns against the pull of the line, which is the whole basis of the self-hooking rigs used in carp and much modern sea fishing.

How anglers navigate a scale with no standard behind it

The working convention is to size the hook to the bait first and to the fish second. A single maggot and a whole squid are different problems, and the fish's mouth sets an upper bound rather than the target.

The second convention is to treat a maker's range as internally consistent and externally approximate: within one pattern from one factory the steps are reliable, and between factories they are not. Anglers who fish several patterns keep to whichever they have calibrated by eye.

Both conventions are widely and independently repeated across the coarse and sea angling literature. Neither is a measured claim, and FishingHQ does not present them as one — they are what experienced anglers do in the absence of a standards body, which is a real form of knowledge and not the same thing as a specification.

Practitioner consensus

Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.

  • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Treatment of hook choice by bait size and species across freshwater angling situations.States this directlyCitation checked — the work exists and is described correctly
  • Sea Angler — Bauer Media (Specialist angling publication)Relied on for: Sea angling practice on hook pattern and size selection for bait presentation.States this directlyCitation checked — the work exists and is described correctly

The mistakes that recur

Reading the aught scale as a continuation of the numbered one, so that a 1/0 is expected to be smaller than a size 1 rather than one step larger.

Assuming the number implies strength. It does not. A size 2 in fine wire will straighten under a load a size 6 in heavy wire will hold.

Sizing to the fish rather than to the bait, which produces a hook so large that the bait sits on it unnaturally and so heavy that a cautious fish rejects it.

Buying across brands on the number alone and then concluding that the pattern has changed when what changed was the factory.

Where to go next

Gear this affects

What these connections rest on (3)

Practitioner consensus — 3 connections

Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.

  • Hooks

    The sizing convention is trade practice with no standards body behind it, which is precisely why it needs an explainer rather than a specification.

    • IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: Tackle definitions and the dimensions by which tackle is specified.Background and mechanism onlyPassage read and verified
    • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: British freshwater practice on tackle selection and its reasoning.States this directlyCitation checked — the work exists and is described correctly

  • Maggots

    Sizing to the bait rather than to the quarry is the standing convention in coarse fishing.

    • IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: Tackle definitions and the dimensions by which tackle is specified.Background and mechanism onlyPassage read and verified
    • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: British freshwater practice on tackle selection and its reasoning.States this directlyCitation checked — the work exists and is described correctly

  • Sea deadbaits

    Gape clearance on large baits is standard sea and predator practice.

    • Sea Angler — Bauer Media (Specialist angling publication)Relied on for: Sea angling practice on tackle and presentation in tidal water.States this directlyCitation checked — the work exists and is described correctly
    • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comparable reasoning from the freshwater tradition, independently arrived at.Background and mechanism onlyCitation checked — the work exists and is described correctly

Related reading

What these connections rest on (1)

Practitioner consensus — 1 connection

Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.

  • How hooks are sized, and what the numbers mean

    A mechanism edge from a record to the explanation beneath it. How tackle behaves is established practitioner knowledge reported consistently across independent traditions, and the label says that rather than claiming a test that was never run.

    • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: Comprehensive angling practice including rods, reels, lines, terminal tackle and the reasoning behind the choices.States this directlyCitation checked — the work exists and is described correctly
    • Still-Water Angling — MacGibbon & Kee, 1953 (Specialist angling publication)Relied on for: Stillwater angling practice including rod design reasoning, line choice, hooks and the mechanics of playing fish.States this directlyCitation checked — the work exists and is described correctly

How this compares

What these connections rest on (1)

Practitioner consensus — 1 connection

Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.

  • Hook points, patterns and penetration

    The two are conventionally specified together on a packet and confused with each other constantly.

    • IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: Tackle definitions and the dimensions by which tackle is specified.Background and mechanism onlyPassage read and verified
    • Freshwater Fishing — Macdonald & Jane's, 1975 (Specialist angling publication)Relied on for: British freshwater practice on tackle selection and its reasoning.States this directlyCitation checked — the work exists and is described correctly

Sources for this page

  • IGFA International Angling Rules and World Record Requirements — International Game Fish Association (Angling or fisheries organisation)Relied on for: Rules on hook construction, spacing and permitted configurations, which describe hooks in terms of measurable dimensions rather than maker size codes.Background and mechanism onlyPassage read and verified

How FishingHQ labels evidence is explained in the evidence policy.

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