How to Choose a Fish Finder: Sonar Types, Screen Size & What Actually Matters

How to Choose a Fish Finder: Sonar Types, Screen Size & What Actually Matters

Whether you're a weekend bass angler or a serious tournament competitor, a quality fish finder changes the way you fish. The problem? The technology has exploded over the past decade — CHIRP sonar, Side Imaging, Down Imaging, MEGA Imaging, LiveScope — and it's easy to overspend on features you don't need or underspend and regret it on the water.

This guide cuts through the noise and walks you through every decision you'll face when choosing a fish finder, from transducer basics to the latest live sonar technology.

How a Fish Finder Actually Works

A fish finder sends sound waves (sonar) from a transducer mounted on your hull down through the water. Those waves bounce off fish, structure, and the bottom, then return to the unit, which translates the data into a visual display.

The transducer is the most important component — more on that shortly. The head unit (the screen) is what you interact with. Most modern units combine both sonar and GPS, which is why you'll also see them called "combo" units or chartplotters.

Sonar Types: The Biggest Decision You'll Make

Not all sonar is equal. Here's what each type shows you and who it's best for.

Traditional 2D Sonar

The classic. A cone-shaped beam sweeps directly below the boat and displays a scrolling graph of what it finds — bottom depth, bottom composition, fish arches, baitfish schools.

Best for: All-around fishing, especially vertical jigging and deep water. Every unit has this.

CHIRP Sonar

CHIRP (Compressed High-Intensity Radar Pulse) sends a continuous sweep of frequencies rather than a single pulse. The result is dramatically sharper target separation — you can distinguish individual fish in a school, and bottom detail is much cleaner.

Best for: Anyone serious about fishing. CHIRP is now standard on most mid-range and up units. If a unit doesn't offer CHIRP, skip it.

Down Imaging / DownScan

Projects a thin, high-frequency beam straight down and produces a near-photographic image of structure, laydowns, and bottom composition. Fish show as distinct "blobs" or streaks against structure — less useful for identifying suspended fish in open water, excellent for finding how fish relate to structure.

Best for: Structure fishing, dock fishing, ledge fishing.

Side Imaging / SideScan

Sends a thin beam out to both sides of the boat simultaneously, covering 100–200+ feet of bottom on each side. Reveals coves, creek channels, ditches, rock piles, and brush piles you'd never find otherwise. One of the most effective tools for pre-fishing a new lake.

Best for: Locating new structure and cover. Game-changing for tournament anglers and anyone fishing unfamiliar water.

Mega Imaging (Humminbird) / Ultra High-Definition Sonar (Garmin)

The highest-resolution version of Side and Down Imaging. Humminbird's MEGA Imaging and MEGA Live use frequencies up to 1.2 MHz for stunning image clarity — you can identify individual tree branches in a laydown. Garmin's equivalent is MEGA LiveScope.

Best for: Anglers who want the best image quality available.

Live Sonar (Garmin LiveScope / Humminbird MEGA Live)

The newest category — and the one that's changed tournament fishing most dramatically. Live sonar shows real-time, near-video-quality images of fish movement, so you can watch fish approach and react to your bait. It's extraordinary technology with an extraordinary price tag.

Best for: Serious anglers who fish competitively or want the absolute cutting edge. Expect to spend $1,500–$2,500+ for the transducer alone.

Screen Size: How Big Do You Need?

Screen size is measured diagonally. Bigger isn't always better — it depends on your boat and mounting position.

Screen Size Best Fit
5–7 inch Small aluminum boats, kayaks, jon boats, secondary units
9–10 inch Bass boats, center consoles as a primary unit
12–16 inch Tournament rigs, larger boats with a dedicated electronics station
16+ inch Multi-unit setups, offshore boats

Resolution matters more than size. A 7-inch unit at 1024×600 shows more detail than a 9-inch unit at 800×480. Look for the pixel count in the specs.

GPS and Mapping: Built-In vs. Add-On

Most modern combo units come with built-in GPS and a base map. Here's what to know:

  • Built-in maps (like Garmin's BlueChart or Humminbird's Basemap) show lakes and coastal outlines but lack detailed depth contours.
  • Premium map cards (Navionics, LakeMaster, Garmin Lake Vu HD) add 1-foot contour lines, which are essential for finding depth breaks, creek channels, and underwater structure. Budget $80–$150 for a quality map card.
  • Auto Chart / Quickdraw — both Garmin (Quickdraw Contours) and Humminbird (AutoChart Live) let you record your own custom depth maps as you fish. Free and extremely useful for your home lake.

The Transducer: The Part Most People Ignore

The screen gets all the attention, but the transducer determines what you actually see. A few key points:

  • Included transducers on budget and mid-range units are adequate but not exceptional.
  • Upgrade your transducer if you want Side Imaging, Down Imaging, or MEGA Imaging — these require specific transducers (not all are bundled with the unit).
  • Mounting options: Transom mount (most common), trolling motor mount (excellent for forward-facing sonar), thru-hull (best for fast boats, requires drilling).
  • Frequency: Higher frequencies (455–1200 kHz) produce sharper images in shallower water. Lower frequencies (50–83 kHz) penetrate deeper but with less detail.

Budget Guide: What You Get at Each Price Point

Under $200 — Entry Level

Basic 2D CHIRP sonar, small screen (5–7"), GPS. Good for casual anglers on small boats. Brands: Garmin Striker series, Humminbird Helix 5.

$200–$500 — Mid-Range

CHIRP + Down Imaging, 7–9" screen, GPS with map upgrades available. The sweet spot for most recreational anglers. Brands: Garmin Striker Plus 9sv, Humminbird Helix 7 CHIRP DI GPS.

$500–$1,000 — Enthusiast

CHIRP + Side Imaging + Down Imaging, 9–10" screen, built-in networking, premium mapping. Where serious anglers start. Brands: Humminbird Helix 10 MEGA SI+ GPS G4N, Garmin ECHOMAP Ultra 106sv.

$1,000–$2,500 — Advanced

MEGA Imaging, large screens (12–16"), full networking, LakeMaster maps, multi-unit compatibility. Tournament-ready. Brands: Humminbird SOLIX 10 MEGA SI+, Garmin GPSMAP 8610xsv.

$2,500+ — Professional

Live sonar (LiveScope/MEGA Live), 15–22" screens, full chartplotter capability, offshore-capable. Brands: Garmin GPSMAP 8617 with LiveScope, Humminbird APEX 19 MEGA Live.

Beginner / Small Boat: Humminbird Helix 5 CHIRP GPS G3 — simple, reliable, affordable.

Bass Fishing Weekend Angler: Humminbird Helix 7 CHIRP MEGA DI GPS G4 — Down Imaging and MEGA sonar at an accessible price.

Serious Recreational Angler: Garmin ECHOMAP Ultra 106sv — 10" screen, ULTRA High-Definition SideVü, built-in LakeVü maps.

Tournament / Competitive: Humminbird SOLIX 12 MEGA SI+ G3 or Garmin GPSMAP 8612xsv — full feature set, networking capable, pairs with Live Sonar.

Quick Decision Checklist

Before you buy, answer these five questions:

  1. What size boat? → Determines ideal screen size
  2. Fresh water or saltwater? → Saltwater needs corrosion-resistant housing and different maps
  3. How deep do you fish? → Shallow (<20 ft) benefits from high-frequency; deep water needs low-frequency
  4. Do you fish new lakes or one home lake? → New lakes justify Side Imaging; home lake anglers may not need it
  5. What's your budget, all-in including map card and transducer? → Don't forget the transducer and maps in your total

Ready to find your unit? Browse our full selection of fish finders from Garmin and Humminbird.

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