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Fishing line calculator and hook sizes

How much line fits your reel, which hook suits fish and bait, and what does casting weight mean?

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Guide sections: Learn to fish: Line calculator

Baits by region Methods Lures Fishing tips Rigs Knots Gear Beginner gear Line calculator Pond fishing

Convert line capacity

The spool says for example 150 m / 0.30 mm. Enter that and the diameter of your line.

Length on spool (m) Diameter on spool (mm) Your line (mm)

How it works: the spool volume stays the same and the line cross-section grows with the square of the diameter. New length = length × (spool diameter ÷ your line)². Braid is not perfectly round, so expect a little less.

Hook size by fish and bait

For small hooks the higher the number, the smaller the hook, so an 18 is much smaller than a 2. That scale ends at size 1. Then come 1/0, 2/0, 3/0 and so on, and from here the hook gets bigger as the number before the /0 rises.

Fish	Bait	Hook size	Sources
Roach	Maggot (1 or 2)	18 to 14	1 2 3
Common bream	Sweetcorn or maggot	16 to 12	1 2
Tench	Maggot or sweetcorn	16 to 12	1 2
Tench	Worm	10 to 8	1 2
Common carp	Boilie	10 to 2	1 2 3
Common carp	Tiger nut or corn stack	8 to 4	1 2
European eel	Lobworm	10 to 1	1 2
European perch	Worm	10 to 4	1 2
Northern pike	Deadbait on trebles	8 to 4	1 2
Zander	Deadbait on trebles	8 to 4	1 2
European flounder	Lugworm	4 to 1	1 2
Atlantic cod	Lugworm and ragworm (big bait)	2 to 6/0	1 2
Bluegill	Piece of worm, cricket or maggot	10 to 6	1 2
Atlantic mackerel	Feathers or sabiki-style string of lures	4 to 3/0	1 2
Largemouth bass	Texas-rigged soft plastic worm	2/0 to 4/0	1 2 3
Channel catfish	Cut bait	2 to 3/0	1 2

Line diameter by fish

Fish	Mono	Braid	Sources
Northern pike	0.30 to 0.40 mm	·	1 2
Common carp	0.30 to 0.40 mm	·	1 2
Zander	·	0.12 to 0.16 mm	1 2
Wels catfish	·	0.30 to 0.70 mm	1 2

Casting weight

The casting weight printed on the rod is the upper limit: lure and sinker together should not weigh more when you cast. A rod marked 30 g takes 30 g at most.
For light spinning for trout and perch, the Bavarian fishing exam gives a casting weight up to about 30 g.
For mackerel from piers and high rocks sources give 60 to 80 g casting weight, and about 40 g where you do not have to lift the fish out.

Ranges from at least two sources per row, no products. When in doubt, go one size smaller.

Sources (6)

Last checked 2026-10-23. Found a mistake? Write to [email protected].

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