How to Choose a Fish Finder

Humminbird Helix 5 SI/GPS Fish Finder, a top fish finder

How to Choose a Fish Finder

Choosing a fish finder isn’t easy. There are so many numbers, specs, options, and more that can make the process seem a lot more complicated than it actually is. These tools can make fishing a lot simpler and allow you to make it more of a science to increase your catch rate consistently, but first you have to choose the correct one for your style. There are a few numbers and options to make note of. These are frequency, depth, cone angle, down imaging, side imaging, GPS, and sensors. If you want, click here to look at the best shallow water fish finders and click here to look at the best fish finders under 300 dollars after reading this.


Frequency is one of the first items to take a look at. The frequency is measured in kHz, or kilohertz. Basically, the higher the frequency, the better the details on screen showing fish, structure, and more. However, higher frequencies often do not read back in very deep water, so they are normally used inland on shallow lakes under a few hundred feet. Frequencies can range from as little as 15 kHz to 800 kHz with down imaging.

The most standard frequency found on lakes inland is 200 kHz. This is good enough to get as much detail as you need, while still able to reach down to good depths. If you really fish only lakes under 150 feet, you can use imaging frequencies of up to 800 kHz, which is good enough to get you a still picture of the bottom. Most often, this high frequency is used through what companies call down imaging or side imaging, which can give you a clear picture of the bottom around you.

As frequencies get up around 400 to 800, the prices start getting high, but this type of clarity can really help you hone in on structure and bait schools. For most anglers, 200 kHz is outstanding and does the job of showing them the generic structure. If you fish deep lakes like the Great Lakes, you will want to look into something with a lower frequency like 83 or 55 to reach the depths and show you the entire water column.

The rule of thumb with frequency is the higher you get, the more clear of a picture you will get but the lower the depth, while the lower you get, the less clear the picture but the greater the depth.


Depth is an important consideration that ties in hand in hand with frequency. A good rule is to get a fish finder that can fish deeper than the deepest lake you fish, but not too much, otherwise you will compromise frequency. You want the highest detail you can get for the depth you fish. You can purchase fish finders that are thousands of dollars that will give you both depth and clarity, but these are beyond most people’s budgets.

Cone Angle

Frequencies are emitted in a cone like shape. The transducer that sends the signal down is the narrow end, while the frequencies get wider the further down they go. Manufacturers measure the angle of this cone to tell you how much ground your fish finder is showing you at certain depths. A 45° angle shows you the same ground diameter as depth you are fishing. For example, if you are fishing 30 feet of water, a 45° cone angle will show you a circle 30 feet in diameter around your boat. A 60° angle will give you slightly more (1.15 times depth), while a 20° will give you about one-third the depth you are fishing. For example, at thirty feet, you will get a 10 foot circle on the bottom with a 20° angle while you would probably get close to a 35 foot circle with the 60° angle.

Generally, as the angles get bigger and bigger, the frequency must go down and therefore the sensitivity gets lower. At 60°, you will frequently find fish finders that will measure it at 83 kHz, while at 20°, you will find fish finders that measure it at 200 kHz. Many fish finders are able to measure both of these through what manufacturers called dual-beam transmission, which you can switch between.

The purpose of this is to allow you to use the lower frequency but wider cone angle to search for structure and schools of fish, while you would use the higher frequency but smaller cone angle to narrow in on the fish and the structure itself.

The exception to this is side imaging. New technology has allowed some manufacturers to send high frequencies off at angles like 80° to give you a clear picture of what is to the sides of your boat. These aren’t effective at great depths, but work very well for shallower water. This will be discussed further down.

Down Imaging

Click this picture to view this Down Imaging Fish Finder

Down imaging, shown above, is basically crystal clear images that are created by sending high frequencies down. These frequencies generally start around 400 and go up to around 800, and will give you a very clear idea of what is on the bottom, as you can see. These aren’t very effective at great depths, but work up to a couple hundred feet. If you fish for fish that often sit around structure, these are the way to go. They may not work quite as well as sonar at identifying fish because they make everything closer to it’s actual size in proportions to the bottom. However, many species of fish like walleye, bass, and crappie choose to hang close to structure and down imaging is what will help you find it.

Side Imaging

Click this picture to view this Side Imaging Fish Finder

Side imaging is shown above. These are high frequency waves that are sent out to the side at extreme angles, normally close to 85°. They give you a very clear image of what is to the side, and normally you can see great distances off to the side with these. These are even better than down imaging at locating structure, as you would merely have to make a few passes over an area you know to contain structure to pinpoint exactly where you want to fish. These are extremely handy for shallow water fisherman, but don’t do much past 150 feet.


Click this picture to view this Fish Finder with GPS

If you want to track where you have been, locate points, dropoffs, and more, and mark waypoints, you need to purchase a fish finder with a GPS. Most of these are able to be integrated with maps of lakes, so you can cruise from spot to spot looking for structure and fish. You can also track your journey so you don’t get lost and so you can follow the same path next time, or just mark waypoints of where you caught fish to come back again as well.


Fish finders can come with many different sensors that can help you make fishing even more of a science if you keep a careful journal. These are water temperature, boat speed, time, GPS coordinates, and more. Look carefully at your options and normally you will have to pay a little more for some of these options, but they are worth having so you can start noticing patterns.


Fish finders seem pretty complex when you first start looking for one, but once you know exactly what you are looking for, they become a lot easier to understand. Click here to look at the best shallow water fish finders and click here to look at the best fish finders under 300 dollars.

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