Every number on this site — width, height, screen area, PPI, combined desk width — comes from one of a handful of plain geometry formulas applied to the diagonal size and aspect ratio you enter. Nothing is looked up from a manufacturer database and nothing is guessed. This page shows the exact math, the assumptions behind it, and where it can't substitute for a spec sheet.
The Core Formula: Diagonal + Aspect Ratio → Width & Height
A monitor's diagonal, width, and height form a right triangle — the diagonal is the hypotenuse, and the width and height are the two legs. If you know the diagonal (D) and the aspect ratio as a width-to-height ratio (W:H), the Pythagorean theorem gives you the actual width and height:
This is the same relationship a manufacturer uses to publish panel dimensions, and it's the only calculation every other number on this site is built from. You can see it applied live in the Visual Size Comparison tool — change the diagonal or aspect ratio and the width/height readouts update instantly using this exact formula.
Worked Example: 27″ 16:9 vs. 34″ 21:9
Two monitors that sound very different on a spec sheet can turn out closer in size than expected once you run the numbers:
| 27″ 16:9 | 34″ 21:9 | |
|---|---|---|
| Width | 23.53" | 31.25" |
| Height | 13.24" | 13.39" |
| Screen area | 311.5 in² | 418.4 in² |
The 34″ ultrawide is 7 inches larger on paper, but it's only 0.15″ taller than the 27″ — almost the entire extra diagonal length becomes width, not height. Its total screen area is about 34% larger, but that comes from a much wider desk footprint, not a taller picture. This is exactly the kind of thing a diagonal measurement alone can't tell you, and it's the core reason this tool exists. Try your own pair of sizes in the comparison tool.
Screen Area (and Why It's Not What You'd Guess)
Once width and height are known, area is simply:
Because area grows with the square of size while a diagonal number is linear, two screens with similar diagonals can have meaningfully different areas once their aspect ratios differ — as the example above shows. It also means a "smaller-sounding" diagonal can occasionally have more area than a larger one; the 32" vs. 34" ultrawide comparison is a real example of that.
Aspect Ratios This Tool Supports
The Visual Size Comparison and Multi-Monitor Setup Simulator support 16:9, 21:9, 32:9, 16:10, 4:3, and 3:2. Build Your Own Monitor Setup additionally supports 5:4. Every ratio is applied through the same formula above — none are hard-coded exceptions.
Pixels Per Inch (PPI)
When you enter a resolution alongside a diagonal size, PPI is calculated the same way manufacturers calculate it:
Higher PPI means more pixels are packed into the same physical space, which is why a 27″ 4K monitor (about 163 PPI) looks noticeably sharper than a 27″ 1080p monitor (about 82 PPI) at the same viewing distance, even though the screen size hasn't changed. See this worked for any size/resolution pair with the PPI calculator.
Multi-Monitor & Custom Setup Calculations
The Multi-Monitor Setup Simulator arranges every monitor in a single row and reports combined width as the sum of each monitor's individual width, plus a bezel gap multiplied by the number of gaps between them (not per monitor) — for three monitors, that's two gaps. Its "tallest screen" readout is simply the tallest single monitor in the row, since mismatched heights don't add together.
Build Your Own Monitor Setup works differently, because monitors there can be dragged anywhere, including stacked or offset. Its total width and height come from the bounding box around every monitor's actual position — the smallest rectangle that contains the whole arrangement — and total area is the sum of each individual monitor's own area (overlapping monitors are not counted twice as desk space, but their areas are still added for the screen-real-estate total).
Curved Monitors
Curved options are offered at 1800R, 1500R, and 1000R — standard radius notation, where a smaller number means a tighter curve. Curvature changes how a screen is drawn and roughly how it wraps around your field of view, but it does not change the width, height, or area numbers calculated above. This matches how curved monitors are actually specified: manufacturers publish the flat, corner-to-corner width and height, with curvature listed as a separate radius spec — a curved panel isn't measured along its curve.
Bezel & Multi-Monitor Spacing
The Multi-Monitor Simulator defaults to an 8mm gap between adjacent screens, adjustable from the bezel slider. This number is a reasonable mid-range assumption, not a measurement of any specific monitor — real bezel width varies by model, and some monitors are markedly thinner or thicker than others. Treat the combined-width figure as an estimate that gets more accurate the closer your slider setting is to your actual monitors' bezels.
Desk Fit & Viewing Distance (Build Your Own Setup)
The desk-depth check compares your entered desk depth against a fixed 25cm typical monitor-stand footprint — this figure does not multiply by monitor count, because monitors in a row sit side by side, not stacked front-to-back; adding more of them increases the width you need, not the depth. Viewing-angle estimates use the standard optical field-of-view formula, angle = 2 × atan((size / 2) / distance), applied to your setup's full bounding box.
Accuracy & Limitations
These calculations are geometric estimates, not physical measurements of any real product. Specifically, they do not account for:
- Chassis and stand dimensions — only the screen area itself is calculated, not the plastic housing, stand footprint, or VESA arm around it.
- Actual bezel width — every real monitor's bezel is a little different; the multi-monitor gap is a single adjustable assumption, not a per-model lookup.
- Curvature's real-world footprint — a curved monitor's front-to-back depth and slightly shorter straight-line width aren't reflected in the flat width/height numbers, by design (see above).
- Manufacturer rounding — some brands round published dimensions differently than strict geometry would produce.
Use these numbers to compare options and plan a setup — not as a replacement for the official spec sheet of a monitor you're actually about to buy.