It's great to return wild trout, salmon and pike so that they can survive and add to the spawning stock, but it's also nice to know how big your catch is, and in the UK at least it has been the tradition to record weight rather than length. Now there is no need to put a fish through extra stress and delay involved in weighing it, because you can get a pretty good estimate of the weight of a trout, salmon or pike from its measured length.
The formulae used in the calculator below is:
Trout and Salmon Weight (in pounds) = (Length x Girth x Girth)/800 where Length and Girth are expressed in inches.
Pike Weight (in pounds) = (Length x Girth x Girth)/900 where Length and Girth are expressed in inches.
If you have recorded only the length measurement, the calculator will automatically insert the typical girth measurement (58% of the length) expected for a fish of that size. (Hen fish tend to have bigger girth measurements than cock fish of the same length; also, lake trout are often deeper-bodied than river trout, so measuring girth is definitely worthwhile if you need an accurate result).
No tape measure? No problem! Length can be recorded against a position (relative to the top of the butt cork or to one of the rod rings, for example, as we did with the 11.5lb sea trout shown here), Make a mental or written note - 'two inches above the butt ring', for example - so that it can be checked with a tape measure when you get back home.
For estimating the weight of a sea trout or a salmon, just use the 'Trout' calculator - it still gives you a pretty accurate estimate of the weight.