Does anyone know how I can estimate aproximate weight of a rainbow trout if I know the length? Earlier this summer I caught a 25 incher and today a 23 incher and I’m wondering how heavy they were. I have inches marked on my rod so it’s easy to determine length without harming the fish before release. I know there is a formula for length and girth but obtaining the girth isn’t practicle, so I’m looking for something that uses only length realizing that this alone won’t be the most accurate.
The standard formula is length times girth times girth, then divide by 800. A 23 inch trout, where I live, is around 4#, 25" one, around 5#. But I have caught 24" trout that went over 8, and a 29" one that went about 6. Depends on how fat they are, thus the girth portion of the formula.
Dennis
I believe the girth is needed,Length by itself cannot determine weight.
I would trim a piece of tippet the girth of the fish then measure it later. For a better estimate.
Congrats BTW!! Nice Fish!!!
JJ
If you are catching trout that size, it does not matter how much they weigh. Just keep on doing what ever you have been doing. :lol:
There are specific formulas for specific species of fish to ESTIMATE weight based on length or length & girth.
There are LOTS of generic calculators on the Internet that will calculate weight for a given length by fish type. Google: “fish length to weight”.
If you want a LOT of information that you can digest by species & location and VERY specific length to weight charts go to [url=http://www.fishbase.org/search.php:cf292]this[/url:cf292] website. I warn you that it is VERY detailed and a bit tricky to figure out what you are looking for.
To find the length/weight relationship FACTORS; type in the common name of the fish you are after and click SEARCH and a list of fish and their locations will pop up. Pick the location you want and after getting to that fish’s summary page; scroll down to the MORE INFORMATION section and click on L-W Relationship.
It is a bit confusing to figure it all out but it works great if you want to build a simple calculator in Excel for specific fish species. The measurements are in metric values so you also have to factor the conversions into it as well. Even if this site makes your head explode there is a lot of other great information there to investigate.
But I?m with JC on this one; if you ain?t in a bass fishin? contest and fishin? for the money; just knowing I caught a 25? trout is good enough for me.
The standard formula is:
1 - estimate the length
2 - add three inches
3 - estimate the weight
4 - add 30%
This should keep you comparable with most fisherman.
:lol: :lol:
Amen brother.
For what it’s worth, our Nebraska Game & Parks Commission publishes AVERAGE weights for several species, based on lengths only, in order to encourage quick release of trophy fish. For rainbow trout their chart shows:
6" = 0.1 pound
9" = 0.3
12" = 0.7
13" = 0.9
14" = 1.1
15" = 1.4
16" = 1.7
17" = 2.1
18" = 2.5
19" = 2.9
20" = 3.4
21" = 4.0
22" = 4.6
23" = 5.2
24" = 6.0
25" = 6.8
26" = 7.7
27" = 8.6
An NGPC fisheries biologist emphasized that these are average weights, based on thousands of fish measurements, but the actual weight range for any given length can be considerable.
Start by talking the weight up on the high side, then talk it down gradually untill your buddies stop shaking their heads and Nod. That will be about the right weight. Jax
Great topic, but I have one even greater!! :lol:
Fisherman aren’t born liars, but they soon overcome it!
if it is a average size trout, and you arent going to take the time to measure the girth with tippet, subtract from 20. So a 5 pounder and a 3 pounder. Actually I think this is more for steelhead which may be a bit more streamlined than resident trout. And again you really have to measure girth.
And don’t forget the “How Many Fish” calculation.
If you catch 2 fish then tell people you caught 15.
But if you catch 15 tell them you only caught 2.
And don’t forget the “How Many Fish” calculation.
If you catch 2 fish then tell people you caught 15.
But if you catch 15 tell them you only caught 2.
How tru is that!
According to Gierach, you’re only supposed to add 2 inches to the length. 
As for weight, round up. 9 ounces = a pound, 6 ounces is about a pound. That’s why I favor the English system of measurement over the metric system. The metric systems seems entirely too neat and precise for fishermen and -women. 8)
Ed
Largest Rainbow trout I ever caught was 23 pounds measured on a butchers scale.
So now when I estimate I use 23 pounds as a base and go up from there. :lol: :lol: :lol:
When asked how much did it weigh? I say . “Trout? Oh about 23 and a 1/2 pounds.” The asker need not know that the 1/2 pound is the one I just caught today and the 23 pounds was from 1966. :lol:
I agree with JC, don’t worry about the weight, just keep doing what you are doing!!
Them is some NICE fish, take some pics, if you remember the camera, not like someone whom I won’t mention
Byron,
“Et tu Brute??”
Mark
:lol: Marco, both tnriverman and me, and you ALSO??? :shock: