Sonar
What size is a 9 inch chartplotter, actually, in inches?
Quick answer
A display's stated size is its diagonal, not its width or height. A 9 inch 16:9 screen measures about 7.8 by 4.4 inches, while a 4:3 screen of the same 9 inch diagonal is wider top to bottom and has more total glass area.
A chartplotter's advertised size is always the diagonal measurement of the glass, the straight line corner to corner across the screen. Width and height are not printed on the box, but they fall straight out of the diagonal and the aspect ratio using ordinary geometry: a right triangle where the diagonal is the hypotenuse.
The console cutout question people actually have is not answered by the diagonal alone. Two screens with the same stated size can be genuinely different shapes, and a wider, shorter 16:9 screen fits differently in a helm than a squarer 4:3 screen of the identical diagonal. The screen also is not the unit: the housing, bezel and flush mount cutout are all larger than the glass, by an amount only the manufacturer's own installation template gives.
On this page
Why the same diagonal is not the same screen
Width and height come from the diagonal and the aspect ratio together. For a 16:9 screen, the diagonal splits proportionally 16 parts wide to 9 parts tall; for a 4:3 screen the same diagonal splits 4 parts wide to 3 parts tall. Because a shape closer to a square packs more area into the same diagonal line, a 4:3 screen at any given diagonal has more total glass than a 16:9 screen at that same diagonal, even though the diagonal number on the box is identical.
16:9 screen dimensions at every stocked size
Nearly every current chartplotter and fish finder screen ships in 16:9, the widescreen ratio. Here is the actual width and height at each size sold.
A 9 inch 16:9 screen measures about 7.84 by 4.41 inches, and a 12 inch screen measures 10.46 by 5.88 inches.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Diagonal (in) | Width (in) | Height (in) |
|---|---|---|
| 4 | 3.49 | 1.96 |
| 5 | 4.36 | 2.45 |
| 6 | 5.23 | 2.94 |
| 7 | 6.10 | 3.43 |
| 9 | 7.84 | 4.41 |
| 10 | 8.72 | 4.90 |
| 12 | 10.46 | 5.88 |
| 16 | 13.95 | 7.84 |
Screens like a 5 inch ECHOMAP through a 12 inch Ultra 2 run this same 16:9 geometry across the whole size range.
16:9 versus 4:3 at the same diagonal
A square is the most efficient shape for a given diagonal, which is why a 4:3 screen has more usable area than a widescreen 16:9 screen at an identical stated size. The gap grows with screen size: at 16 inches a 4:3 screen carries over 13 more square inches of glass than a 16:9 screen of the same diagonal.
At a 9 inch diagonal, a 4:3 screen carries 38.88 square inches of glass against 34.57 square inches for the 16:9 screen at the same size.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Diagonal (in) | 16:9 width × height (in) | 16:9 area (sq in) | 4:3 width × height (in) | 4:3 area (sq in) |
|---|---|---|---|---|
| 4 | 3.49 × 1.96 | 6.84 | 3.2 × 2.4 | 7.68 |
| 5 | 4.36 × 2.45 | 10.68 | 4.0 × 3.0 | 12.00 |
| 6 | 5.23 × 2.94 | 15.38 | 4.8 × 3.6 | 17.28 |
| 7 | 6.10 × 3.43 | 20.92 | 5.6 × 4.2 | 23.52 |
| 9 | 7.84 × 4.41 | 34.57 | 7.2 × 5.4 | 38.88 |
| 10 | 8.72 × 4.90 | 42.73 | 8.0 × 6.0 | 48.00 |
| 12 | 10.46 × 5.88 | 61.50 | 9.6 × 7.2 | 69.12 |
| 16 | 13.95 × 7.84 | 109.37 | 12.8 × 9.6 | 122.88 |
Every aspect ratio in the catalog, compared at 7 inches
Beyond 16:9 and 4:3, a smaller number of units still ship in 16:10 or 5:4. Holding the diagonal fixed at 7 inches shows how much the shape itself changes the usable glass.
At an identical 7 inch diagonal, a 5:4 screen carries 23.90 square inches of glass against 20.92 for the 16:9 screen, because a shape closer to a square is more efficient for a given diagonal.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Aspect ratio | Width at 7 in diagonal (in) | Height at 7 in diagonal (in) | Area (sq in) |
|---|---|---|---|
| 16:9 | 6.10 | 3.43 | 20.92 |
| 16:10 | 5.94 | 3.71 | 22.04 |
| 4:3 | 5.60 | 4.20 | 23.52 |
| 5:4 | 5.47 | 4.37 | 23.90 |
How far away can you comfortably read it?
No chartplotter or fish finder manufacturer publishes a recommended viewing distance. The column below is a derived planning figure built from general human factors work on legible character height at a working distance, roughly 200 times the character's own height, and a screen character rendered at about 1/28th of screen height. Treat it as a rough estimate, not a specification.
A character rendered at roughly 1/28th of screen height is comfortable to read from about 200 times its own height away, which works out to under 3 feet for a 9 inch display and is a planning estimate rather than anything a maker publishes.
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.
| Diagonal (in) | 16:9 screen height (in) | Derived comfortable viewing distance (ft) |
|---|---|---|
| 7 | 3.43 | 2.0 |
| 9 | 4.41 | 2.6 |
| 10 | 4.90 | 2.9 |
| 12 | 5.88 | 3.5 |
| 16 | 7.84 | 4.7 |
No manufacturer publishes a recommended viewing distance for a marine display. This column is derived from general legibility research rather than any marine specification and should be treated as a rough planning figure, not a rating.
Frequently asked questions
How is a chartplotter screen size measured?
The advertised size is always the diagonal, the straight line measured corner to corner across the visible glass, not the width or the height. This is the same convention televisions and monitors use. Two chartplotters with the same stated diagonal can still be different physical shapes if they use different aspect ratios, which is why the diagonal alone does not tell you whether a unit fits a given cutout.
Why does a 4:3 screen have more area than a 16:9 screen at the same diagonal?
A shape closer to a square is geometrically more efficient at packing area into a fixed diagonal line than a wide, short rectangle is. A 16:9 screen is stretched wider and shorter for the same diagonal, which trims usable area compared with a 4:3 screen of the identical stated size. The difference grows as the diagonal gets larger.
Is the bezel included in the stated screen size?
No. The stated diagonal measures the visible glass only. The housing, bezel and the flush mount cutout a unit actually needs in a console are all larger than the glass, and by an amount that varies by model. The manufacturer's own installation template is the only reliable source for cutout dimensions, not the diagonal on the spec sheet.
How far away should I be able to read my chartplotter?
No manufacturer publishes a recommended viewing distance for a marine display. A rough planning figure derived from general legibility research suggests comfortable reading at roughly 200 times the height of a displayed character, which works out to a few feet for most console mounted screens, but this is an estimate rather than a specification any maker stands behind.
Do bigger chartplotters always use 16:9?
Nearly all current units from Garmin, Lowrance and Humminbird use 16:9, since it matches the wide format of split screen chart and sonar views. A small number of older or specialty units use 4:3 or other ratios. Checking the specification sheet for width and height, not just the diagonal, confirms which shape a specific model actually is.
Does screen size affect touchscreen usability?
Larger screens generally make touch targets easier to hit accurately and allow more comfortable split screen layouts of chart, sonar and radar together. A 7 inch screen is workable for a single view but gets cramped with a split, while 9 inches and larger are where most anglers say a two or three pane layout stops feeling crowded.
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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.