Calculator › Knives › Fillet knife
A fillet knife is the thinnest blade in the shop: 0.040–0.070 in at the spine for a 6–7 in blade (up to 0.100 in for a 10 in salmon knife) so it flexes along the bone. That thin, it is stock removal only, and stainless is strongly preferred because the knife lives around fish and water. AEB-L in 0.040–0.062 in is the classic choice and is sold in sheet and narrow bar.
Width is under 1 in for most of the blade, so 1 × 1/16 in stock in 36 in lengths gives three or four blades. Keep the tang the same thickness and let the handle do the stiffening.
Steel is only part of the cost. Add abrasives, handle, heat treat and your time, and see the price that actually pays you.
Copy link to this calculationOne job, done well: running a blade along a fish's backbone and rib cage, and separating flesh from skin. The blade bends so it can follow the skeleton and stay in the plane of the skin, which is what keeps meat on the fillet instead of on the frame. It is not a boning knife for red meat and it is not for prying at joints or cutting through heavy bone.
The modern pattern has a clear origin. Ron Weber, a Minnesota tackle rep, sketched a consumer fillet knife after seeing commercial fish-house knives worn thin and flexible by years of sharpening, and had the Finnish maker Lauri Marttiini build it. Marttiini doubted it would sell; Weber ordered twenty thousand. The Rapala Fish 'n Fillet launched in 1967, came with an instruction booklet because the real barrier was that anglers did not know how to fillet, and has sold in the tens of millions since.
Flex is a spec, not a virtue — more is not automatically better. High flex suits skin removal and small fish; medium is the versatile choice if you clean several species; stiff is for large, dense or thick-skinned fish and heavy ribs. Length tracks the fish: roughly 4–6 in for panfish, 6–7 in for walleye and bass, 7–9 in and up for big saltwater. Stainless is close to mandatory — this knife lives in slime, blood and salt water away from a sink — and the old line that stainless is brittle and won't hold an edge is simply wrong: AEB-L was designed as razor-blade steel, has carbides under a micron, and takes a finer edge than most carbon steels. Two other things get returns: too much hardness in a blade that must bend to its elastic limit and spring back, and a beautiful stabilised handle that turns slick the moment it is wet.
Thin stainless moves in heat treat. Plate quench between aluminum blocks straight out of the foil, and temper twice before you look at the edge or you will chase a warp that was going to relax anyway.
| Panfish, 5 in blade | 3/4 × 0.040–0.050 in |
|---|---|
| Standard, 7 in blade | 1 × 1/16 in |
| Salmon, 9–10 in blade | 1 1/4 × 3/32 in |
Widths assume blade height + 1/8 in rounded up to stock; thickness is the finished spine rounded up. Change the inputs above for your own pattern.
Not sensibly. At 1/16 in the steel loses heat in seconds and warps if you look at it. Grind it from thin stainless stock.
Bar sizes for ten common knife patterns, weight per inch for every standard flat bar, and quick heat-treat numbers for the usual carbon steels. Print it, tape it to the grinder.