## Estimating Weight of Largemouth Bass

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January 22, 2017

Several methods are available to estimate the weight of a fish. Some use length as well as girth measurements. Weight also can be estimated using only length measurements based on relationship between length and weight. Length-weight equations can be developed for specific waters, regions (e.g., states), or for a particular species.

Formulas containing length as well as girth are often most accurate for estimating weight, because the fatness or plumpness of the fish is accounted for. If only length is available, the most accurate weights often are estimated from length-weight relationships for specific waters or regions. For instance, in some waters fish might be relatively «skinny,» and the weight estimate might be overinflated if based on a formula created from data on a water body where fish are «fat» or even «normal.» That’s why adding girth to the formula can help with accuracy. Formula’s containing girth, however, also may not be as accurate as we’d like, because of inherent differences in the shape of fish and finding the right adjustment factor (or «shape» factor) to use in the formula. And it’s important to measure girth carefully, and at the fish’s fattest point, as girth estimates affect weight estimates powerfully.

One easy way to estimate fish weight is through the use of standard length-weight formulas. Species-specific formulas, called standard-weight equations, have been developed for dozens of fish species by fishery biologists to describe the standard growth form of a species as a whole. These relationships often are used to assess body condition (the relative weight or plumpness of a fish), which provides an index of a fish’s well-being, such as whether there are forage shortages or surpluses, and can sometimes reflect fish growth rate.

These standard length-weight formulas are often developed using thousands of fish from hundreds of populations across the range of a species, so they describe the «general» growth form of that species. For instance, the equation for black crappie was developed using over 20,000 fish across a range of sizes from 175 populations across the geographic range of black crappie.

*An important thing to keep in mind is that these standard length-weight formulas describe fish in «above-average» condition. In fact, the weights in the tables represent the 75th-percentile in the samples for that particular length, and are not average weights. In other words, if you lined up 100 random bass of the same length in order of weight, and those bass were a good representation of the range of weights for that length, the weight provided in the table would be for the 75th heaviest fish. While it might have made more sense to use the median weight for these formulas, fishery biologists decided to go with the 75th percentile so that the standard weight at a given length was an above-average or «ideal» target to shoot for in terms of body condition. So, if your fish appears plump and healthy, the weights from the table should be relatively close. If your fish is skinny to average, it will weigh less, and if very plump and remarkably «fat» it will weigh more. Just make an adjustment. No formula is 100-percent accurate, but if you have only length and not girth, this should help get you in the ballpark. Your state fishery agency may have standard Largemouth Bass Length To Weight Conversion Chart based on regional data posted on their website. These formulas use total length of the fish, measured from the tip of the snout to the tip of the tail fin when compressed.

Largemouth Bass | |

12 in | 0.90 lb |

13 in | 1.16 lb |

14 in | 1.47 lb |

15 in | 1.83 lb |

16 in | 2.25 lb |

17 in | 2.73 lb |

18 in | 3.28 lb |

19 in | 3.89 lb |

20 in | 4.59 lb |

21 in | 5.36 lb |

22 in | 6.22 lb |

23 in | 7.17 lb |

24 in | 8.21 lb |

25 in | 9.35 lb |

26 in | 10.60 lb |

27 in | 11.95 lb |

28 in | 13.42 lb |

29 in | 15.01 lb |

30 in | 16.73 lb |

31 in | 18.58 lb |

32 in | 20.56 lb |

This information is provided for those who wish to hold “paper” fishing events, releasing bass immediately after catch instead of holding them for weigh-in. Figures in the conversion table below represent average weights calculated from statistics on 3,178 Texas bass. By using this table, you can get a reasonable estimate of a fish’s weight.

This method is not accepted for official fish records and will never be as accurate as weighing on a certified scale, but it can be helpful at slot limit lakes, or for fishing clubs that wish to provide better care for bass during the hot summer months when fish are easily stressed.

- Measure the bass to the nearest eighth of an inch.
- Go down the first (left-hand) column and locate the row corresponding to the length of your fish in whole inches.
- In the “Fractions” columns across the top of the table, find the nearest eighth of an inch that matches the length of your bass.
- Read down the column to find the estimated weight in pounds.

For example, you want to find the weight for a bass that is 18¼ inches long. Find 18 inches in the first column, then move across the table to the 1/4-inch column. Read the estimated weight of 3.46 pounds (3 pounds, 7.4 ounces).

Inches | Fractions | |||||||
---|---|---|---|---|---|---|---|---|

0 | 1/8 | 1/4 | 3/8 | 1/2 | 5/8 | 3/4 | 7/8 | |

10 | 0.48 | 0.50 | 0.52 | 0.54 | 0.56 | 0.58 | 0.61 | 0.63 |

11 | 0.66 | 0.68 | 0.71 | 0.73 | 0.76 | 0.79 | 0.81 | 0.84 |

12 | 0.87 | 0.90 | 0.93 | 0.97 | 1.00 | 1.03 | 1.07 | 1.10 |

13 | 1.14 | 1.17 | 1.21 | 1.25 | 1.29 | 1.32 | 1.37 | 1.41 |

14 | 1.45 | 1.49 | 1.54 | 1.58 | 1.63 | 1.67 | 1.72 | 1.77 |

15 | 1.82 | 1.87 | 1.92 | 1.97 | 2.02 | 2.08 | 2.13 | 2.19 |

16 | 2.25 | 2.31 | 2.36 | 2.42 | 2.49 | 2.55 | 2.61 | 2.68 |

17 | 2.74 | 2.81 | 2.88 | 2.95 | 3.02 | 3.09 | 3.16 | 3.23 |

18 | 3.31 | 3.39 | 3.46 | 3.54 | 3.62 | 3.70 | 3.78 | 3.87 |

19 | 3.95 | 4.04 | 4.13 | 4.22 | 4.31 | 4.40 | 4.49 | 4.58 |

20 | 4.68 | 4.78 | 4.87 | 4.97 | 5.08 | 5.18 | 5.28 | 5.39 |

21 | 5.49 | 5.60 | 5.71 | 5.82 | 5.94 | 6.05 | 6.17 | 6.28 |

22 | 6.40 | 6.52 | 6.64 | 6.77 | 6.89 | 7.02 | 7.15 | 7.28 |

23 | 7.41 | 7.54 | 7.68 | 7.81 | 7.95 | 8.09 | 8.23 | 8.38 |

24 | 8.52 | 8.67 | 8.82 | 8.97 | 9.12 | 9.27 | 9.43 | 9.59 |

25 | 9.75 | 9.91 | 10.07 | 10.23 | 10.40 | 10.57 | 10.74 | 10.91 |

26 | 11.09 | 11.26 | 11.44 | 11.62 | 11.80 | 11.99 | 12.17 | 12.36 |

27 | 12.55 | 12.74 | 12.94 | 13.13 | 13.33 | 13.53 | 13.73 | 13.94 |

28 | 14.15 | 14.35 | 14.56 | 14.78 | 14.99 | 15.21 | 15.43 | 15.65 |

29 | 15.87 | 16.10 | 16.33 | 16.56 | 16.79 | 17.03 | 17.26 | 17.50 |

## Length to weight conversion tables

Length/Weight Conversions for Marine Fishes of Texas

Data and formulas are from studies conducted by TPWD and other scientific groups

All lengths are total lengths unless fork length (FL) or lower jaw to fork length (LJFL) is indicated.

Select fish and enter length in inches:

Length to Weight Conversions

These tables give a very good indication of the weight of each species of fish covered;- Tope, Pike and Salmon. By using these tables you can minimise the amount of stress and potential damage to your catch, returning them to the water in a better condition.

Tope

(reproduced by kind permission of the UK Shark Tagging Programme)

Tope anglers are encouraged not to weigh tope (for reasons of welfare of the fish) unless they have an appropriate weighing sling.

An indication of weight can be obtained by measuring length and obtaining an estimate of weight using a length to weight conversion chart, similar to the one that follows.

Total length is measured from tip of nose to end of tail.

Length (inches) | Approx Weight (lbs) |
---|---|

24 | 6 |

26 | 6 |

28 | 7 |

30 | 8 |

32 | 9 |

34 | 9 |

36 | 10 |

38 | 11 |

40 | 12 |

42 | 13 |

44 | 15 |

46 | 16 |

48 | 18 |

50 | 19 |

52 | 21 |

54 | 23 |

56 | 26 |

58 | 28 |

60 | 31 |

62 | 34 |

64 | 37 |

66 | 41 |

68 | 45 |

70 | 49 |

72 | 54 |

74 | 59 |

76 | 65 |

78 | 71 |

80 | 78 |

Length (cm) | Approx Weight (kg) |
---|---|

61 | 3 |

66 | 3 |

71 | 3 |

76 | 4 |

81 | 4 |

86 | 4 |

91 | 5 |

97 | 5 |

102 | 5 |

107 | 6 |

112 | 7 |

117 | 7 |

122 | 8 |

127 | 9 |

132 | 10 |

137 | 10 |

142 | 12 |

147 | 13 |

152 | 14 |

157 | 15 |

163 | 17 |

168 | 19 |

173 | 20 |

178 | 22 |

183 | 24 |

188 | 27 |

193 | 29 |

198 | 32 |

203 | 35 |

Pike

Length (inches) | Appriox Weight (lbs) |
---|---|

39 | 22 |

41 | 27.25 |

43 | 32.25 |

45 | 37 |

47 | 42 |

49 | 47 |

51 | 53 |

53 | 56.75 |

Length (cm) | Approx Weight (kg) |
---|---|

100 | 10 |

105 | 12 |

110 | 15 |

115 | 17 |

120 | 19 |

125 | 21 |

130 | 24 |

135 | 26 |

Salmon

Length (inches) | Approx Weight (lbs) |
---|---|

20 | 3 |

22 | 4 |

24 | 6 |

26 | 7.5 |

28 | 9 |

30 | 10.5 |

32 | 12.5 |

34 | 15 |

36 | 18 |

38 | 21 |

40 | 24 |

42 | 27 |

44 | 30.5 |

46 | 33.5 |

48 | 36.5 |

50 | 39.5 |

52 | 42.5 |

Length (cm) | Approx Weight (kg) |
---|---|

50 | 1.5 |

55 | 2 |

60 | 2.5 |

65 | 3.5 |

70 | 4 |

75 | 5 |

80 | 5.5 |

85 | 7 |

90 | 8.5 |

95 | 9.5 |

100 | 11 |

105 | 12.5 |

110 | 14 |

115 | 15 |

120 | 15.5 |

125 | 18 |

130 | 19 |