How Long Is A Trout – Measuring & Weighing

With much talk about knowing the length of a catch, we decided to put an end to the question of how long is a trout?

So how do you accurately weigh and measure trout?

measuring and weight a trout is important

A beautiful brook trout!

Does size and how long is a trout really matter?

Absolutely, size does matter, how else can you adequately brag about the “big one” you just caught?

Seriously though, Conservation Officers are particular about how long is a trout, especially the one in your catch. Unless you are OK with paying a nasty fine for trout that doesn’t meet the size requirements, let’s do the job properly the first time.

In this article we’re going to look at three types of measurements: total lengthgirth, and weight.

What problems arise when figuring out how long is a trout?

How hard is it to accurately measure a wet, wiggly fish on a hot day (rhetorical question)? Starting out with the right tools can help a lot.

Tools for accurately weighing your catch:

As with anything related to fishing, getting the right gear for the right job is important. For weighing and measuring your catch you will need:

  • Fish grabber to hold the fish securely and safely
  • Tape measure or ruler (for length)
  • Bump board (for length)
  • Retractable or fabric tape measure (for measuring girth)
  • Hook scale (for weight)

Most common mistakes when measuring trout for length, weight and girth:

Here are a few of the most common mistakes when trying to get specifics on how long is a trout:

  • Many people aren’t sure what parts of the fish are specified when trout measuring
  • Using the wrong measuring tool for the job. Fabric tape measures work well for getting the girth, but move too freely to get an accurate length reading.
  • Using a flexible tape measure along the curve of the fish. Fish and length measurements should all be taken when the fish is lying flat.
  • Not squaring the fish. A popular way of winging the measurement process is by putting a sticker or line (usually on the uneven ground or deck) as a starting point and literally laying down the fish and measuring. There is too much margin for error with this “system”.
  • Forgetting to zero out the hook scale (not subtracting the weight of the sling from the total weight).
  • Not closing/zipping the sling of the hook scale (as the trout moves around it will interfere with the weight and can injure your catch.
  • Hold the hook scale from the loop provided (don’t cup the scales).

Have you done any of the above? Never fear, follow our step-by step guide to measuring your next trout.

Measuring total length:

The Total Length (TL) is the full length of the fish (mouth closed) and the tail fin pinched together (total length is used in slot limit and minimum landing size regs).

The best way to get this length is to gently push the fish’s snout up against a vertical surface with the mouth closed and the fish lying along a tape measure. Then pinch the tail fin closed and determine the total length.

1) Be sure to have all the tools that you need on hand: tape measure, ruler, or bump board (more on bump boards below).

2) Lay the fish straight out.

3) Close the mouth of the fish and pinch the tail fin.

4) Remember, the TL measurement starts at the outside of the lip and runs all the way to the end of the pinched tail, measuring straight and flat (preferably along hard surface). Do not measure along the curve of the fish, it’s simply a straight length measurement.

As simple as the steps above may sound, the execution of those steps rarely goes according to plan!

The easiest way to measure length: use a bump board

We prefer using a bump board. This is a tool to help line up a fish for measuring and is usually lightweight, compact and simple to use.

Bump boards are easy to make (there are many tutorials on YouTube using either plastic or wood as a base).

The bonus is that this technique is what the CO uses. If making your own board, be sure that the numbering is clear and large enough to see when you take a photo of the fish on the board. That way, if there is some shrinkage after the catch has been sitting on ice for a while, you will still have visual proof of the catches’ original size.

Why use a bump board?

  • Easier to square up the fish for the most accurate measurement;
  • Doesn’t harm the fish (for catch and release);
  • Easy to take a photo of the fish on a bump board to eliminate;
  • Available in a variety of materials (vinyl, plastic, even sealed wood); some can even easily be rolled or folded up for easy storage.

Sounds tricky but honestly, it gets easier as you get used to thinking about how long is a trout.

Measuring the girth

Unlike length, girth is best measured with a fabric ruler (like a tailor might use) or by using a piece of string.

Measure the fish around the widest point, marking where the ruler overlaps (like measuring your waist). The measurement should be taken perpendicular to the length of the fish.

The girth measurement is important to certify a fish for a record and provides useful information about the condition of a fish.

​Measuring the weight

You can pick up a small, inexpensive, and accurate hook scale online or at your favorite outdoor shop.

1) Start by zeroing the scale. Be sure to add the sling or double bag a plastic grocery bag to the hook before zeroing out the scale. In other words, the scale should read “0” even with the bag or sling attached.

2) Carefully place your catch in the sling/bag and hold the scale by the top loop provided.

3) Take the measurement and photograph for future bragging rights!

No matter what method you use for assessing how long is a trout, always make sure that the catch is over the size limit – don’t take chances on this! Not only is it potentially expensive, but taking trout that are too small has a longer term impact in depleting stocks before fish are ready.

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