To measure your arm, place your elbow against a wall and then the end of a tape measure against the wall.
Photo by Rachel Barlow

During my time as a guide I quickly learned that most anglers have no idea how to judge the size of a fish by sight. Two-thirds of my customers would look at a 12-inch and say, “Man, that must be fifteen, sixteen inches, right?” while the other third landed a 22-inch rainbow and asked, “Do you think it’s 18?” Inches are?” In this internet trolley era, accidentally overestimating the length of a fish can lead to an avalanche of abuse that’s no fun. So it’s worth learning how to measure a fish, but the most important thing is to do it fast.

This is important as the amount of time you keep a fish out of the water is extremely important. The “Keep ‘Em Wet” ethos is rampant these days, and studies by the Colorado Division of Wildlife have shown that it’s possible to keep the fish in the water while unhooking it double his chances of survival. So what you need is a way to get a near-instant measurement of the fish you’ve caught.

Working as a guide, I experimented with several methods until I finally settled on what I felt was the quickest and easiest method: I measured my own forearm, from the tip of my elbow to the tip of my middle finger. (Some of you old timers or Latin fans might recognize this measure as ell.) The total distance is just under 19 inches. From the elbow to the bump in my wrist is 10 inches, to the base of my pinky is 15 inches and to the end of my pinky is 17 inches. I was able to memorize these numbers easily and was able to make a very educated estimate for an inch or two either side of these points.

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A Tape measure on a zinger means less time wasted rummaging through bags.
Photo via

Whenever I landed a fish for a client, I could hold the fish just below the surface, place my forearm next to it, and take an instant rough measurement. Sure, it wasn’t exact – and as a guide: may I’ve rounded up on occasion – but this method lets you know instantly if a fish is closer to 15″ than 18″. I also know that the width of my spread hand is 8.5 inches from the end of the pinky to the end of the thumb. Anything over 19 inches is of course a bit more complicated.

In this case I would mark the 19″ spot, run my hand to the nose of the fish, and then guess in reverse order. Just add the two numbers and you’re good to go. (Example: tail forward to mark = 19″, nose back to mark = tip of middle finger to base of pinky, so 4″. 19+4 = 23″ fish.) Anything above that, let’s say 25″. , and face it , you put out the damn tape.

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If you must use the tape measure, make sure the fish stays in the water.
Photo by Sandy Hays

What I particularly like about this method is that you don’t have to worry about anything other than the fish. However, many anglers like to use their rod as a measuring stick. Jay “Fishy” Fullum, a well-known fly tyer and angler, recommends using thread wraps on your rod blank. He makes narrow wraps of 12, 14, 16, 18 and 20 inches. You can use easy to read, high visibility colors or if you feel this detracts from the aesthetics of your rod use colors to match the guide sleeves. If you want to measure a fish, simply put the rod in the water next to the fish and estimate based on your windings.

Both methods require far less rummaging in pockets or arranging things on the vest, saving precious seconds between the time you land the fish and the time you let it swim away. And if your friends can’t live without a measurement that’s absolutely scientifically verifiable, just make new friends. It’s better for the fish that way.