Made with love and a passion for displays. The idea for DisplayMath came when I travelled to London from abroad to see The Odyssey at BFI IMAX. I wanted to know how the screen would look from my cinema seat compared with my living-room TV from my usual seat at home. I needed a tool to make that comparison, so I built one.
How this screen size calculator works
A screen size really comes down to two numbers: resolution and diagonal. From those, this calculator works out the physical width and height, pixel density, and how much of your view the screen fills from where you sit. It also draws every display to scale on a single canvas, so you can see the size difference instead of guessing at it.
Calculate screen width and height from the diagonal
A 27-inch monitor or 65-inch TV is measured diagonally across the visible screen. To find its width and height, you also need the aspect ratio. For a flat 16:9 screen, width = diagonal × 16 / √337 and height = diagonal × 9 / √337. Use inches throughout, then multiply by 2.54 to convert to centimeters. Resolution changes pixel density, but it does not change the dimensions at the same diagonal and aspect ratio.
A 65-inch TV has about 40% more screen area than a 55-inch, even though the diagonal is only 18% larger. See the 55 vs 65 inch TV size comparison for a drawing and viewing angles from the same couch. For a desk, compare 24 vs 27 inch monitors . Use the calculator above for ultrawide, portrait or curved screens; their aspect ratios and physical footprints differ from this table.
What is PPI (pixels per inch)?
PPI tells you how many pixels fit in one inch of screen. To get it, divide the diagonal resolution in pixels by the diagonal size in inches. Higher PPI means sharper text and finer detail at the same viewing distance. A 27-inch QHD monitor comes in around 109 PPI, while the same size in 4K reaches about 163 PPI. A 55-inch 4K TV sits near 80 PPI, which is perfectly fine because you watch it from much farther away.
Will it look sharp from my seat?
Pixel density and viewing distance both affect visible detail. The PPD calculator combines them into central pixels per degree, with a clearly labelled 60 PPD reference. It is a comparison aid, not a guarantee that pixels or resolution differences become invisible.
What is field of view?
The field of view angles tell you how much of your vision the screen spans at your viewing distance. Two screens with the same angles look the same size from your chair, whatever their physical dimensions. As a reference, THX recommends a picture that fills about 40 degrees of your view for a cinematic experience. The field of view canvas draws that as a dashed ray, so you can see at a glance whether a screen reaches it.
How far should you sit?
The cinematic seat row gives the distance for a 40 degree horizontal field of view. It is a starting point for an immersive picture, not a comfort requirement. The what size TV calculator starts with your room and lets you adjust the viewing angle. The mounting height calculator checks screen placement against your seated eye line.
What is pixel pitch?
Pixel pitch is the center-to-center spacing of neighbouring pixels, the inverse of PPI. A 27-inch QHD panel has a pitch of about 0.233 mm; LED walls are specced this way directly, with pitches measured in whole millimetres. Hover the row for the value in micrometres and pixels per centimetre.
How much of your vision does a screen cover?
Your horizontal field of view spans roughly 200 degrees, but it is far from uniform. Truly sharp vision comes from the fovea, only about a degree wide, backed by a parafoveal region of about 5 degrees where reading actually happens. You can recognise shapes and symbols out to about 30 degrees, identify color out to about 60 degrees (also roughly where the binocular overlap between your two eyes ends), and beyond that you mostly just detect motion. Switch the canvas to field of view mode to see your displays drawn inside these zones.
See a screen at real size on your wall
On a supported iPhone or iPad, every display card has a "View in AR" button. It opens your camera in augmented reality with a slab of exactly that screen's physical dimensions, anchored to your wall or floor at true scale, so you can check whether a 65-inch TV overwhelms the living room before buying it. The old trick was outlining the size in painter's tape; this is the same idea without the tape. Scaling is locked, so what you see is the honest size.
What does OS scaling do to a sharp display?
High-density screens are rarely run at 100%: Windows and macOS scale the interface up so text stays a comfortable physical size. Enter your scale factor and the looks-like row shows what you actually work with. A 27-inch 4K panel at 150% behaves like a 109 PPI screen with a 2560 by 1440 workspace: the interface uses the panel's native pixels, with QHD amounts of workspace. The sweet spot for unscaled use sits around 110 PPI; much past 140 PPI you will want scaling.
What does 1800R mean on a curved monitor?
The R number on a curved monitor is the radius of its curve in millimetres, so an 1800R panel follows a circle with a 1.8 m radius. Smaller numbers mean a tighter curve. At a viewing distance equal to the radius, points along the horizontal centre line of a cylindrical panel are equally far from your eyes. Choose a distance that suits the picture size and your posture. Because the panel bends, its straight-line width (the chord) is shorter than the screen surface itself. That chord is the measurement that decides whether a curved monitor actually fits on your desk.
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