Salmon Fly Size Calculator   


I've been fishing for Atlantic Salmon for the best part of 40 years, and every time I arrive, at a river the questions that go through my mind are what fly, how big how deep?

Fly selection for a particular river is a matter of local choice – some flies seem to do better on a particular river, & whether that’s because everyone is using the same ones, or not is debatable – if the ghillies are saying “you must use a Posh Tosh”, then it stands to reason that the Posh Tosh will come out top of the catch list that week, even though a Willie Gunn may have been a better choice! – We’ll never know, but I’d love to see some research on this.

It is a truth widely acknowledged that at water temperatures below 9°c, the angler is probably better off on a sinking line – the precise depth being determined by the speed of the current and depth of the river.  Slow deep stretches are often best fished very deep, but faster shallow streams will not allow the use of very fast sinking lines.

The enigma that always troubled me most was that of fly size selection – so many factors to be taken into account – Water temperature, speed, river height and colour.  Many years ago Trout & Salmon magazine gave away a wheel calculator, which attempted to resolve these inputs to a suggested fly size, and through the use of that device, with some subtle changes, I decided to write the Fly Size calculator app for my own use. 

Having used it, and discussed its suggestions with a number of ghillies, they have confirmed that it supplies the same sizes that they would be using – surprisingly big at times to my reading of the river, but in other circumstances smaller that my instincts would suggest.   Nevertheless, in the words of one, “it does what it says on the tin”!  I suppose that all that proves is that no matter how long one has been fishing, you don’t always read the river correctly, or you allow the influence of one factor outweigh the impact of others.

To use the app, now available on the iTunes store here , you enter the water temperature, speed of the current, water height & colour, and at the bottom of the screen the recommended Tube & dressed fly sizes are shown.  These are for traditional flies only, and don’t cover the possibility of using flies such as the Dee Monkey or Sunray Shadows, that sometimes (rarely in my case!) elicit a response from a salmon.

Why pay for it?  Well, my logic in deciding to charge was that it avoided having to fund it by having adverts popping up all over the place, and it gave me the flexibility to retain control over it rather than advertisers.  After all, if you’ve spent upwards of £100 on a days fishing, why use the wrong fly all day, when for £2.99 you can always be on the right size.  One user commented to me that £2.99 was less than the price of a tapered leader, and at least the app lasted for ever, rather than a leader, which was inevitably changed periodically.

Its important to note that the size of tube suggested is the overall dressed fly length rather than that of just the tube body – a 1 ½” tube fly could be on a 1 ½” tube, or even a ½” tube.  You decide, based on the weight of tube & depth you want to fish.

Click here for Screen-shots of the app.

Click here to download it from the iTunes store