Pick a size and see the gap the published charts give it, drawn to scale on your own screen once you have set it with a bank card. Or pick a fish and see the sizes people use for it.
Size 2/0 · 19 of 32 on the scale
Gap 1/2 inThe gap is the distance from the point to the shank.
| Size | Gap | Fish it is charted for |
|---|
A size is not a standard. Hook makers share no benchmark, so a #2 from one maker is not a #2 from another — which is why this page shows what each chart says instead of one number.
Sizes and species ranges checked 2026-09-20.
Quick answer: hook sizes run in two directions that meet in the middle. From #32 up to #1 the hook gets bigger as the number gets smaller. Then the scale switches to aughts, and from 1/0 up to 20/0 the hook gets bigger as the number gets bigger. There is no #0. The measurement that matters is the gap — point to shank — because that is what decides the bait that fits and the mouth it fits. A published chart puts a 1/0 gap at 7/16 in (11 mm) and a 5/0 at 11/16 in (17 mm). Set the scale on the tool above with a bank card and you can hold your own hook against the screen.
How to use it
Pick a size and the tool draws its published gap at life size on your screen, once you have set the scale — drag the box until it matches a bank card, which is 85.6 mm wide everywhere in the world. Pick a fish instead and it moves to the middle of the range published for that fish and marks the whole band on the chart. If the hook in your hand has no packet any more, choose Measure mine, hold it against the ruler and read the size off.
The hook size chart, with gaps
| Size | Gap | Gap in mm |
|---|---|---|
| #6 | 3/16 in | 4.8 mm |
| #4 | 1/4 in | 6.4 mm |
| #2 | 5/16 in | 7.9 mm |
| #1 | 3/8 in | 9.5 mm |
| 1/0 | 7/16 in | 11.1 mm |
| 2/0 | 1/2 in | 12.7 mm |
| 3/0 | 9/16 in | 14.3 mm |
| 4/0 | 5/8 in | 15.9 mm |
| 5/0 | 11/16 in | 17.5 mm |
| 6/0 | 3/4 in | 19 mm |
| 7/0 | 13/16 in | 20.6 mm |
| 8/0 | 7/8 in | 22.2 mm |
| 9/0 | 15/16 in | 23.8 mm |
| 10/0 | 1 in | 25.4 mm |
| 12/0 | 1 1/8 in–1 1/2 in | 28.6–38.1 mm |
| 14/0 | 1 1/8 in–1 1/2 in | 28.6–38.1 mm |
| 16/0 | 1 1/8 in–1 1/2 in | 28.6–38.1 mm |
| 18/0 | 1 3/4 in–2 in | 44.4–50.8 mm |
| 20/0 | 1 3/4 in–2 in | 44.4–50.8 mm |
Sizes smaller than #6 are missing from that table on purpose. The charts this page cites do not publish a gap for them, and rather than make one up the tool shows where they sit in the order and hands you a ruler. The order is not in doubt: a #10 is bigger than a #12, which is bigger than a #14, all the way down to #32.
Two charts, two answers, and why that is the honest result
One published chart gives a size 6 a 3/16 in gap. Another describes a size 6 as having a quarter-inch gap. That is a whole size apart on the same scale, and neither of them is wrong — hook makers have never agreed a benchmark, so a #6 is whatever a given maker’s #6 is. Any page that prints one confident number for every size is hiding that from you. This one shows both figures with the source each came from, which is also why the tool is built around measuring your own hook rather than trusting the packet.
Hook size by fish
These are the ranges Academy publishes by species. Treat them as a starting point: the bait you are using, how the fish are feeding and whether you are releasing them all move the number.
| Fish | Hook size |
|---|---|
| Albacore | 3/0 to 6/0 |
| Alewife | #14 to #10 |
| American Shad | #8 to #4 |
| Arctic Char | #12 to #8 |
| Arctic Grayling | #16 to #10 |
| Atlantic Angelfish | #10 to #6 |
| Atlantic Bonito | 4/0 to 6/0 |
| Bass (smallmouth) | 2/0 to 3/0 |
| Bass (largemouth) | 3/0 to 5/0 |
| Bluefish | 1/0 to 4/0 |
| Bluegill | #12 to #8 |
| Bowfin | 2/0 to 4/0 |
| Carp | #10 to #2 |
| Catfish | 5/0 to 8/0 |
| Cod | 4/0 to 6/0 |
| Flounder | 1/0 to 3/0 |
| Gar | 3/0 to 5/0 |
| Grouper | 8/0 to 12/0 |
| Halibut | 8/0 to 16/0 |
| Herring | #16 to #12 |
| Kingfish | 2/0 to 4/0 |
| Mackerel | 1/0 to 4/0 |
| Mahi-mahi | 7/0 to 9/0 |
| Panfish | #12 to #6 |
| Perch | #10 to #6 |
| Pike | 2/0 to 5/0 |
| Pompano | #4 to #2 |
| Redfish | 1/0 to 3/0 |
| Salmon | 2/0 to 4/0 |
| Skate | 4/0 to 6/0 |
| Snapper | 2/0 to 5/0 |
| Spadefish | #1 to 4/0 |
| Sturgeon | 6/0 to 10/0 |
| Sunfish | #12 to #8 |
| Tarpon | 3/0 to 7/0 |
| Tilefish | 5/0 to 8/0 |
| Trout | #14 to #10 |
| Tuna | 7/0 to 10/0 |
| Walleye | #4 to 1/0 |
| Whitefish | #10 to #6 |
| Yellowtail | 2/0 to 4/0 |
How to measure a hook properly
- Measure the gap, not the length. The gap is the straight distance from the point across to the shank. Total length varies enormously between patterns with the same number.
- Measure at the widest part, square across, not diagonally along the bend.
- Print this page at 100% if you would rather use paper — the ruler prints at true size, and the calibration box is left out of the print.
- A treble is measured the same way, on one of its three points, and fishes bigger than a single of the same number.