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The fish weight calculator allows you to easily estimate the weight of fish by length, girth, and kind. Have you ever gone fishing and taken all the necessary equipment but forgot a scale that would help weigh the fish you just caught? Using this tool, you will never experience the same problem again. You can calculate the weight of fish by length for many species; for example, you can easily convert the length of a largemouth bass to its weight.

What do I need to calculate the weight of a fish by its length?

Fish weight depends on the type of fish you measure. The thicker the fish species is, the more it weighs compared to its length. To calculate fish weight, you will need to know the following:

  • Sish length;
  • Fish girth (optional);
  • Species of the fish...
  • ...or which kind is it most similar to.

How to measure fish length?

Fish standard length is the distance between the tip of the fish's snout and the point where the caudal (tail) fin starts. Total length includes the caudal fin, and it is measured between the tip of a snout and the most posterior part of the caudal fin. It is important to measure it as a straight line. You shouldn't consider the curvature of the fish's body.

Fish measurements, marked fish length and girth.

How to measure fish girth?

Fish girth is the maximal circumference around the fish's body. It shouldn't be mistaken with the body depth, which is the deepest vertical measurement that can be made between the dorsal and ventral portions of the fish.

🙋 If you cannot measure the girth, this fish size calculator will assume its value with the following equation: girth = length × 0.58.

What is the heaviest fish in the world?

The heaviest species of fish known is the whale shark. The adult specimens can grow up to 70 feet in length and weigh up to 47,000 pounds.

Although blue whales are much bigger than whale sharks, they are not classified biologically as fish. They are mammals and are more closely related to the species of land animals, such as cats and dogs, or even us humans.

Do I need a permit to catch fish?

Legal requirements for fishing may vary depending on your location or the season of the year. Before you decide to go fishing, make sure to check the requirements at your local authorities and apply for a license if needed.

And before going to the ponds or river, make sure to check out our fishing reel line capacity calculator. We wish you tight lines and bent rods!

Are the fish I catch healthy and safe to eat?

Fish are a great source of omega-3 fatty acids — contained in fish oil. These fatty acids are essential if you want to maintain heart health and proper brain function throughout your life. Our fish oil calculator can help you calculate the optimal fish oil dosage for you. Fish usually contain low amounts of saturated fats, and are low in calories, which makes them an excellent choice for people seeking to lose weight or just keep a healthy diet.

However, some fish species can contain high levels of mercury, a metal toxic to the nervous system. Its intake is risky, especially for people looking to get or already pregnant, breastfeeding, and young children. You should be cautious if you belong to any of the high-risk groups. The amount of mercury in a fish depends on several factors, and this fish mercury calculator allows you to easily check if the amount of fish you plan to have is safe to eat.


How much does a 20 inch trout weigh?

To calculate the trout-like fish weight, you can use the following equation:

weight = length × girth²/900

Or, if you don't want to do it by hand — use our fish size calculator. The weight of a 20-inch long trout should equal roughly 3 lbs.

How much would a 27 inch largemouth bass weigh?

To transform a 27-inch largemouth bass length into its weight, use the following equation:

weight = length × girth²/800

If you don't know the girth of the fish, our calculator will estimate it automatically. The 27-inch long bass should weigh 8.28 lbs.

How heavy is a 30 inch pike?

The 30-inch pike is estimated to weigh 10 pounds. To calculate it, you can use the following equation:

weight = length³/2700

Jarosław Bąk
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