How heavy should a euro nymph be? Bead sizes, grams and how to choose

A euro nymph should be just heavy enough to reach the slow water near the river bed and drift there without dragging on the stones. In numbers, that usually means a tungsten bead between 2.0 and 4.0 mm, which is 0.05 to 0.48 g of bead. A whole fly weighs more, from under 0.1 g for a small perdigon to near 0.9 g for a heavy #14 jig fly. I sell nymphs for the rivers I guide, and this is how I think about the weight: the chart first, then what the chart cannot tell you.

I have fished competitions for more than ten years, and in competition all the weight is in the fly. There is no split shot and nothing on the leader. So the bead you choose is the whole answer to “how deep”, and it is worth getting right.

The short answer: just heavy enough to reach the slow water near the bed

Water near the bed moves slower than water at the surface. That slow layer, roughly 10 to 50 cm (4 to 20 in) above the stones, is where a nymph drifts naturally and where most fish hold (Swentosky, Troutbitten, 2017). Your fly has to get there and stay there.

Too light, and the fly never reaches the fish. Too heavy, and it drags along the bottom, hangs up, and the drift is dead (Miller, Fly Fisherman, 2025). The right weight sits between the two, and it changes with every run: deeper, faster, or further away means more weight; shallow, slow, or close means less.

The chart: bead diameter, weight, hook size

The figures below are one maker’s own beads (Firehole Outdoors), raw tungsten before paint. Paint adds about 0.01 g. I built the table from their size reference; other brands differ, and I come to that next.

Source: Firehole Outdoors, bead size reference.

Notice how steep the steps are. A 3.5 mm bead weighs about one and a half times a 3.0 mm bead, and more than six times a 2.0 mm bead. Half a millimetre is never a small change.

Which bead fits which hook

From the chart: 2.5 or 3.0 mm. A #14 takes 2.5 to 3.5 mm, a #12 takes 3.0 to 4.0 mm, a #18 takes 2.0 or 2.5 mm, and a #20 takes 2.0 mm. The same hook can carry two or three bead sizes, and that is the point of the next sections: the hook sets the size of the fly, the bead sets how fast it sinks.

Why a chart is only a start

Brands differ

A test of twelve brands of 3.8 and 4.0 mm slotted beads found diameters up to 8 per cent off the label and about 17 per cent between the lightest and the heaviest, and a bigger bead was not always a heavier one (Smith, The Fly Stop). So treat any chart, including the one above, as approximate. If weight matters to you, weigh your own flies.

Alloy matters little

Fly-tying beads are 90 to 97 per cent tungsten. On a 3.0 mm bead, the whole range from 90 per cent to pure tungsten is about 0.02 g; going up half a millimetre adds about 0.12 g (Place, Firehole Outdoors, 2026). Buy the size you need, and do not pay for purity.

Tungsten is the choice because of its density: about 19.3 g/cm³ against 11.34 for lead and 8.73 for brass (Smith, The Fly Stop). A brass bead of the same size is less than half the weight.

Slotted or round

Slotted beads carry more metal than countersunk round ones, and they sit on jig hooks, which ride point up. Round beads go on standard and curved hooks (Firehole Outdoors; Smith, The Fly Stop). A 3.0 mm slotted bead is 0.21 g against 0.18 g round.

Weight is not sink rate

Two flies of the same weight can sink at very different speeds. A slim, smooth fly with a large bead, the perdigon style, cuts through the water and gets down fast. A bulky fly with legs and dubbing catches the current, rides up, and hurries through the drift (Miller, Fly Fisherman, 2025; Murray’s Fly Shop, 2026).

The tippet counts too. Thinner tippet sinks faster and drags less (Costa, 2016).

To put whole flies in numbers, one shop weighed its patterns (Murray’s Fly Shop, 2026; the method is not described, so take the figures as an example):

• #16 perdigon: 0.065 g
• #14 perdigon: 0.105 g
• #16 jigged pheasant tail: 0.22 g
• #14 jigged hare’s ear: 0.32 g
• #16 Blowtorch: 0.335 g
• #12 jigged hare’s ear: 0.54 g
• #16 French Bomb: 0.60 g
• #14 French Bomb: 0.88 g

Their working ranges on their own streams: about 0.50 g and up for high or fast water, 0.25 to 0.40 g for its mid-weight jig nymphs, and under 0.15 g for low, slow, clear water. Those are one shop’s rivers, not a rule for yours, but the shape of it holds anywhere.

The leader changes the answer

A thick leader weighs more in the air between the rod tip and the water. At distance it sags, and the sag pulls a light fly up and towards you. On a standard 20 lb butt, a single #16 bead-head is hard to keep on a tight line much past 6 m (20 ft) (Swentosky, Troutbitten, 2021). On a very thin leader, 2.0 to 2.5 mm beads reach depth in moderate current without any more weight (Daniel, 2023).

So “how heavy” depends on what the fly is tied to. The same nymph fishes two different depths on two different leaders. I cover the thin leaders in micro leaders for euro nymphing.

Choosing on the water

Too light

The sighter moves at the speed of the surface, or faster. You never feel the bed. Go up one bead size, or change to a slimmer fly of the same weight.

Too heavy

The sighter stalls, you feel every stone, and the drift stops and starts. You snag. Takes are hard to tell from the bottom. Go down one bead size.

The sign you are right

When the sighter travels slower than the surface water, the nymphs are in the slow layer (Swentosky, Troutbitten, 2017). On whether the fly should touch the bed: Swentosky prefers to glide the point fly through the zone without touching the stones, and keeps ticking the bed for another rig (Swentosky, 2024). What does not work is a fly that never slows down.

One size up or down

Change weight before you change pattern. Josh Miller carries one simple nymph in beads from 2.0 to 3.8 mm and changes the bead first; his everyday hooks are #16 to #20 (Miller, Fly Fisherman, 2025). His line on it is that “a well-drifted fly is slightly more important than the pattern.” For learning to cast a dry-dropper on a euro leader, Devin Olsen suggests starting with a 2.8 mm bead or larger, so the leader turns over (Olsen, Gink & Gasoline).

What competition rules allow

In competition the weight limit is written down. Under the FIPS-Mouche rules, 2025 edition, weight must be hidden in the dressing and may not go past the bend or the eye of the hook; one visible bead of at most 4 mm is allowed; and nothing that sinks or floats may be added to the leader (articles 28.3 and 29.2). So the biggest visible bead that passes a controller is 4.0 mm, about 0.48 g; more weight may sit hidden under the dressing (article 29.2). The Fly Stop’s test found beads sold as 4 mm that measured over it, which is why several makers sell 3.8 mm (Smith, The Fly Stop).

Those are competition rules, not river rules. On an ordinary day they bind nobody. The full rule set is in FIPS-Mouche rules explained.

Light flies for grayling

Grayling water is often shallow and clear, and the fish are close. On a beck 1 to 4 ft (0.3 to 1.2 m) deep, Dave Southall fishes a #16 nymph with a 2.0 or 2.5 mm bead; on another water his #22 bloodworm carries a 1.5 or 2.0 mm bead (Southall, Sunray, 2020).

The rivers I guide are grayling rivers above all, and the Ćehotina is the one I call a wild euro-nymphing river. What a grayling riffle asks of the nymph, run by run, is in euro nymphing in Montenegro. How grayling sit and take, compared with trout, is in grayling vs trout: lies and takes.

Flies for these rivers, and tying your own

I sell nymphs, dry flies and streamers for all the rivers I guide: see flies. On a multi-day trip a fly tying clinic can be added as a paid extra, with the tools and materials provided, and tying your own weights is the quickest way to learn what the chart means.

How many nymphs to fish, and how far apart, is in one nymph or two. How long the leader, sighter and tippet should be is in leader, sighter and tippet length. The waters themselves are in fly fishing in Montenegro: the complete guide.

Questions

How much does a 3.0 mm tungsten bead weigh?

About 0.2 g: 0.18 g round and 0.21 g slotted, on one maker’s chart (Firehole Outdoors). Other brands differ by a few hundredths.

What size tungsten bead for a size 16 hook?

2.5 or 3.0 mm. Use the smaller one for shallow water and the larger for deeper or faster water.

What is the biggest bead allowed in competition?

4 mm, one visible bead, with any other weight hidden in the dressing (FIPS-Mouche rules, 2025 edition, article 29.2).

Is tungsten much heavier than brass?

Yes, more than twice as dense: about 19.3 g/cm³ against 8.73 (Smith, The Fly Stop).

Do perdigons sink faster than their weight suggests?

Yes. The slim, smooth body meets little resistance, so a perdigon sinks faster than its weight suggests (Murray’s Fly Shop, 2026; Miller, 2025).

How do I know my nymph is too heavy?

The sighter stalls, you feel every stone, and the drift stops and starts. Go down one bead size.

A chart gets you to the water with the right box. Choosing the weight run by run is learned on the river, and I teach it on a guided day or in competition training, with my own nymphs for these rivers if you want them. Tell me your dates and the river you have in mind. Request your dates.