Sonar
Sonar frequency and cone angle chart: coverage by depth and frequency
Quick answer
Cone angle sets sonar coverage: coverage diameter equals 2 times depth times the tangent of half the cone angle. In 10 feet of water a common 20 degree, 200 kHz cone covers a circle about 3.5 feet across, which is why side and down imaging exist for shallow water.
A transducer's cone angle decides how much bottom a single sonar ping actually covers, and the geometry is simple published trigonometry: coverage diameter equals 2 times depth times the tangent of half the cone angle. The angle itself is not something this site can give you. It belongs to the reader's own transducer at the frequency being run, and the manufacturer publishes it, not a general chart.
The typical angles below are the common values repeated across the fish finder market for standard frequencies, useful for understanding the relationship between frequency, angle and coverage, not a guarantee for any specific transducer. Always check the transducer's own specification sheet before assuming a number from this page.
Typical cone angle by frequency
The common traditional beam at 200 kHz runs a 20 degree cone, narrower than the wide 45 to 60 degree cones used for deep water coverage at 50 and 83 kHz.
Rule of thumb Boating and fishing convention rather than a published standard. Taught everywhere, useful, and not a specification. Nothing enforces it and no body publishes it.
| Frequency (kHz) | Typical cone angle | What it is used for |
|---|---|---|
| 50 | 45° | Deep water traditional sonar, wide and low resolution |
| 83 | 60° | Wide traditional beam, more water covered and less detail |
| 200 | 20° | The common traditional beam, the default on most units |
| 455 | 16° | Down and side imaging, narrow along track |
| 800 | 10° | High resolution imaging, shallow range |
These are typical values repeated across the market for each frequency. The transducer's own specification sheet governs for any specific unit, since cone angle is a vessel figure that belongs to the reader's own transducer at the frequency being run, not a standard.
Coverage diameter by depth, at the common 20 degree cone
At the common 20 degree, 200 kHz cone, 10 feet of water covers a circle about 3.5 feet across, which is exactly why a boat in shallow water is looking at almost nothing straight down.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Depth (ft) | Coverage diameter at 20 degrees (ft) |
|---|---|
| 5 | 1.76 |
| 10 | 3.53 |
| 20 | 7.05 |
| 30 | 10.58 |
| 50 | 17.63 |
Coverage diameter by frequency, at a fixed depth
At the same 20 foot depth, a wide 60 degree, 83 kHz cone covers about 23 feet across against about 3.5 feet for a narrow 10 degree, 800 kHz cone, a coverage difference of more than six times.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Frequency (kHz) | Typical angle | Coverage diameter at 20 ft (ft) |
|---|---|---|
| 50 | 45° | 16.57 |
| 83 | 60° | 23.09 |
| 200 | 20° | 7.05 |
| 455 | 16° | 5.62 |
| 800 | 10° | 3.50 |
The angle column repeats the typical values from the first table above. The diameter column is the published trigonometry applied to each one at a fixed 20 foot depth.
Coverage area grows faster than coverage diameter
Coverage area grows with the square of the diameter, so doubling depth from 10 to 20 feet roughly quadruples the area covered, from about 9.8 to about 39 square feet, at the same 20 degree cone angle.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Depth (ft) | Coverage diameter (ft) | Coverage area (sq ft) |
|---|---|---|
| 10 | 3.53 | 9.77 |
| 20 | 7.05 | 39.07 |
| 50 | 17.63 | 244.1 |
Frequently asked questions
What is a sonar cone angle?
A sonar cone angle is the width of the beam a transducer sends toward the bottom, published by the transducer's own maker for each frequency it runs. A wider angle covers more water in a single ping but spreads the returning energy thinner, giving less detail. A narrower angle covers less water but concentrates the return, giving sharper target separation, which is the basic tradeoff behind every frequency choice.
How wide is a 20 degree cone in 10 feet of water?
Using the published coverage formula, coverage diameter equals 2 times depth times the tangent of half the cone angle, a 20 degree cone in 10 feet of water covers a circle about 3.5 feet across. That is the common traditional 200 kHz beam on most entry level fish finders, and it explains why so little bottom is actually visible directly under the boat in shallow water.
Why does a wider cone angle cover less detail?
A wider cone spreads the same transmitted energy across a larger area of bottom, so less energy returns from any single point and two close targets are more likely to blur into one return. A narrower cone concentrates that energy, which is why high frequency imaging sonar such as 800 kHz uses a narrow 10 degree beam to resolve fine detail rather than the wide beams used for deep water coverage.
Does side imaging use the same cone angle math as traditional sonar?
The same trigonometry applies, but side imaging shapes its beam very differently: narrow along the direction of travel and wide fanning out to the side, rather than the roughly circular cone traditional sonar uses straight down. The coverage formula on this page describes a traditional down looking cone specifically, and a side imaging transducer's own specification sheet states its own along track and cross track figures separately.
Where do I find my own transducer's cone angle?
On the transducer's own specification sheet or product listing, not on a general chart. Manufacturers publish the beam angle for each frequency a transducer supports, and it varies by model even within the same brand and even within the same nominal frequency. The typical angles on this page are useful for understanding the relationship between frequency and coverage, not a substitute for the actual published number.
Why does coverage area grow faster than coverage diameter?
Because area scales with the square of the diameter, following the same geometry as the area of any circle. Doubling the coverage diameter roughly quadruples the coverage area rather than doubling it. That is why doubling depth from 10 to 20 feet at a fixed 20 degree cone angle takes coverage from about 9.8 to about 39 square feet, a fourfold jump in area from a twofold jump in depth.
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Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.