Fish-Weight Calculations
In the Pacific Northwest, many native Salmonids cannot be retained, and must be released unharmed. So you catch a truly beautiful native fish, and you want to know how much it weighs, but you know you should not take it out of the water to weigh it. How can you get an accurate weight without weighing it? Simple. Use a formula based on the fish's length and girth to get a very accurate estimate.
The two traditional formulas for calculating the weight of salmonids (salmon and trout) are:
1. (length x girth x girth)/775 = weight in pounds
2. (length x girth x girth)/800 = weight in pounds
Most knowlegable anglers, however, use a newer formula. The most recent formula and most accurate estimation is the Lum formula:
3. length x length x girth x 0.0007 = weight in pounds
This formula was developed by Professor Lewis Lum, head of the Mathematics Department at the University of Portland.
To make it easier, we provide two other options here: A weight calculator and a weight table. Both the calculator and the table use the newer "Lum formula" for weight estimation. It is very accurate. Use whichever one you find easiest.
The Salmonid Weight Calculator
To use the calculator, simply enter the fish's length from the tip of its nose to the tip of its tail. Then enter the girth of the fish, measured just in front of the dorsal fin. All measurements need to be in inches; use decimals for parts of inches, as in 24.5.
Use a cloth tape to measure your fish. Keep the fish in the water. The time a fish spends out of the water is about the same to it the time you can spend under the water! How long could you hold your breath underwater after the fight of your life, when you are still desperately gasping for air? Just because a fish cannot yell at you does not mean it is okay! Keep it in the water to save its life.
Would you like to have this calculator in your boat or at stream side?
When you land one of those gorgeous native fish, before you release it, wouldn't it be nice to know it's weight immediately? Well, you can have it, if you have an iPhone or similar web-enabled phone. Simply go to <this special page> and copy the web address into your phone's web-page bookmarks.
Then, when you catch that trophy native fish, you can use your soft-cloth tape to measure its length and girth, release it, and then call up this little web application and calculate the fish's weight instantly on your phone, while still in your boat or at stream side.
Here's the web address if you want to write it down:
http://www.AnglerInnovations.com/pages/mustknownow.aspx
The Salmonid Weight Table
To use the weight table, you need to know the length and girth of your fish, in inches. Then, go down the left side of the table to the length of your fish, and across the table (to the right) to the girth of your fish. The cell at the intersection of the length and girth is the estimated weight of your fish, in pounds.
For those anglers who fish the saltchuck, it is always nice to have a halibut weight table to consult. We provide one here.
The Halibut Weight Table
Length in inches (Head on) , Net weight in lb. (Dressed, head off),
Round weight (Whole fish, before dressing) in lb.
| Length (inches) | Net wt (pounds) | Round wt (pounds) | Length (inches) | Net wt (pounds) | Round wt (pounds) | |
| 20 | 2.3 | 3.1 | 59 | 77.5 | 103.1 | |
| 21 | 2.7 | 3.6 | 60 | 81.8 | 108.9 | |
| 22 | 3.2 | 4.2 | 61 | 86.3 | 114.8 | |
| 23 | 3.7 | 4.9 | 62 | 91 | 121.1 | |
| 24 | 4.2 | 5.6 | 63 | 95.9 | 127.5 | |
| 25 | 4.8 | 6.4 | 64 | 100.9 | 134.2 | |
| 26 | 5.4 | 7.2 | 65 | 106.1 | 141.1 | |
| 27 | 6.2 | 8.2 | 66 | 111.5 | 148.2 | |
| 28 | 6.9 | 9.2 | 67 | 117 | 155.6 | |
| 29 | 7.8 | 10.3 | 68 | 122.8 | 163.3 | |
| 30 | 8.7 | 11.5 | 69 | 128.7 | 171.2 | |
| 31 | 9.6 | 12.8 | 70 | 134.9 | 179.4 | |
| 32 | 10.7 | 14.2 | 71 | 141.2 | 187.8 | |
| 33 | 11.8 | 15.7 | 72 | 147.7 | 196.5 | |
| 34 | 13 | 17.3 | 73 | 154.5 | 205.5 | |
| 35 | 14.3 | 19 | 74 | 161.5 | 214.7 | |
| 36 | 15.6 | 20.8 | 75 | 168.6 | 224.3 | |
| 37 | 17.1 | 22.7 | 76 | 176 | 234.1 | |
| 38 | 18.6 | 24.8 | 77 | 183.7 | 244.3 | |
| 39 | 20.3 | 27 | 78 | 191.5 | 254.7 | |
| 40 | 22 | 29.3 | 79 | 199.6 | 265.4 | |
| 41 | 23.8 | 31.7 | 80 | 207.9 | 276.5 | |
| 42 | 25.8 | 34.3 | 81 | 216.4 | 287.8 | |
| 43 | 27.8 | 37 | 82 | 225.2 | 299.5 | |
| 44 | 30 | 39.8 | 83 | 234.2 | 311.5 | |
| 45 | 32.2 | 42.9 | 84 | 243.5 | 323.8 | |
| 46 | 34.6 | 46 | 85 | 253 | 336.5 | |
| 47 | 37.1 | 49.3 | 86 | 262.7 | 349.5 | |
| 48 | 39.7 | 52.8 | 87 | 272.8 | 362.8 | |
| 49 | 42.5 | 56.5 | 88 | 283.1 | 376.5 | |
| 50 | 45.3 | 60.3 | 89 | 293.6 | 390.5 | |
| 51 | 48.3 | 64.3 | 90 | 304.4 | 404.9 | |
| 52 | 51.5 | 68.5 | 91 | 315.5 | 419.7 | |
| 53 | 54.8 | 72.8 | 92 | 326.9 | 434.8 | |
| 54 | 58.2 | 77.4 | 93 | 338.6 | 450.3 | |
| 55 | 61.7 | 82.1 | 94 | 350.5 | 466.2 | |
| 56 | 65.4 | 87 | 95 | 362.7 | 482.4 | |
| 57 | 69.3 | 92.2 | 96 | 375.3 | 499.1 | |
| 58 | 73.3 | 97.5 |