Fishing Hook Size Lab

Fishing hooks use two numbering systems. Numbered sizes (#32 up to #1) run backwards: the smaller the number, the bigger the hook, so a #1 is much larger than a #32. Aught sizes (1/0 up to 20/0, pronounced “one-aught”) run forwards: 2/0 is bigger than 1/0, and 10/0 is bigger than 5/0. The system flips direction between #1 and 1/0. Use the size converter above to translate any size into millimetres, inches or gap width.

No — and this is the most important thing to know. There is no accepted definition of “real size”; a #2 from one manufacturer can differ from a #2 from another, and the same number means different dimensions across hook styles (a #2 treble is not the same as a #2 J-hook). Our chart is a cross-brand reference compiled from an Eagle Claw/Trokar size chart, a saltwater gap-width table, Mustad O’Shaughnessy measurements and Shaddock treble data — always check the manufacturer’s chart on the packet for the hooks you actually buy.

For largemouth bass: use a 2/0–4/0 circle hook with live shiners, a 3/0–4/0 EWG (extra-wide-gap) worm hook for a Texas-rigged 5-inch senko, and #2–2/0 hooks for streamers if you fly fish. For smallmouth bass, go slightly smaller: #1–2/0. Match the hook gap to your bait — the point must stay exposed, not buried in the plastic.

A #10 to #14 baitholder or aberdeen hook is the classic PowerBait setup, with #12 the most popular all-rounder. Mould a small marble-sized ball of dough so the point and barb stay exposed. For spinners and spoons, use the treble the lure came with, or swap to a #6–#10 single siwash hook where regulations require single hooks.

A 3/0 or 4/0 EWG (extra-wide-gap) worm hook is the standard for a 5-inch senko on a Texas rig; drop to 2/0 for 4-inch finesse worms. The wide gap keeps the point clear of the thick plastic so hooksets penetrate. This is one of the most searched hook questions, and the answer is the same across US, UK and Australian bass-style fishing.

Channel catfish: 2/0–5/0 circle hooks with cut bait or punch bait. Bigger flathead and blue catfish: 6/0–10/0 circle hooks with live or large cut bait. Circle hooks are ideal for catfish because they hook in the corner of the mouth as the fish swims away — just reel tight instead of jerking the rod.

Carp on a hair rig: #6–#8 wide-gape hooks; on a float with corn or bread: #10–#12. Tench: #10–#14 with small baits like maggots, casters or soft pellets. Tilapia: #8–#12 with tiny dough balls or bread — tilapia have small mouths, so downsizing gets more bites. These coarse species overlap heavily, which is why one hook wallet covers all three.

For live and natural bait, yes in most cases: circle hooks rotate and catch the corner of the mouth as the fish swims away, giving healthier releases and fewer gut-hooked fish. Do not strike — just reel tight. J-hooks are better when you need to set the hook yourself: cut bait on the bottom, hard-mouthed fish, or trolling. Note that circle hooks are legally required in some fisheries, e.g. non-offset, non-stainless circle hooks with natural bait in the Gulf reef fish fishery.

The gap is the distance from the shank to the point. It is the measurement that decides what size bait fits and what size mouth the hook can grab. A gap buried inside bulky bait cannot set — the point must stay exposed. As a rule of thumb, choose a gap roughly as wide as the thickest part of your bait. The converter above lists the gap width of every size in mm and inches.

With calipers or a ruler, measure (1) total length: from the top of the eye to the bottom of the bend, and (2) gap width: from the inside of the shank to the point. Enter either measurement in the converter’s “find by measurement” box and it will return the closest standard sizes. Because sizes are not standardised, treat the result as the nearest match, then confirm against the manufacturer’s chart.

Treble hooks use the same numbering as single hooks (#18 up to 10/0), and the size refers to each of the three points — a #4 treble has three #4-sized points on one shank. A #4 treble is about 22.1 mm tall with an 8.9 mm gap (Shaddock measurements). Trebles come stock on most crankbaits and spoons; many anglers swap them for single siwash hooks for easier release and to comply with single-hook regulations.

The X rating is shorthand for tippet diameter: 0X is 0.011 inch (0.279 mm), and each step up in X is one thousandth of an inch thinner — so 5X is 0.006 inch (0.152 mm) and 8X is 0.003 inch (0.076 mm). The rule of 3 matches tippet to fly: divide the fly size by 3 to get the X rating (a #15 fly ≈ 5X). Strength varies by material and brand; the table above lists typical nylon breaking strains from 0X down to 8X.

Yes — the #/aught numbering is international. A 3/0 in the UK, Australia, New Zealand or South Africa is the same nominal size as a 3/0 in the US; only the recommended species change by region (e.g. tailor and Australian salmon instead of striped bass). Our converter and charts work worldwide — switch between mm, cm and inches with the unit toggle.

European sea bass: 2/0–4/0 for live bait, 1/0–3/0 on lures. General inshore saltwater (redfish, snook, flounder): 1/0–3/0 circle hooks. Offshore species step up fast: king mackerel and cobia 4/0–7/0, grouper 5/0–8/0, tuna 7/0–12/0, sharks 8/0–20/0. See the saltwater/circle sub-chart above for the full species table with gap widths.

It depends on the water. Some fisheries are barbless-only, and circle-hook rules apply to certain species and areas (for example the Gulf reef fish fishery and several Atlantic billfish tournaments mandate circle hooks). Barbless or pinched barbs also make catch-and-release faster and less damaging. Always check your local regulations before fishing — rules on hook type, size limits and seasons vary by location.

Yes. Open the Actual Size tab, pick a hook size, and use your browser’s print function with scaling set to 100% (or “Actual size” / “None”). The print view includes a 100 mm calibration ruler — measure it after printing; if it is not exactly 100 mm, adjust the scale. On-screen 1:1 rendering assumes a standard 96-DPI display; compare the on-screen calibration strip with a real ruler or a credit card (85.60 mm wide) to verify.