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 pixels per degree 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 cover the same angular area from your chair, whatever their physical dimensions; their perceived scale and immersion can still differ. 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?
The combined horizontal field of both eyes spans roughly 200 degrees, with about 120 degrees of binocular overlap; these extents vary between people. Detail is strongest near the centre of your gaze and decreases gradually towards the periphery. The drawing uses total angles: 10° and 60° as intermediate guides, 120° for approximate binocular overlap and 200° for approximate peripheral extent. It ends at the next guide that contains the widest display, with a minimum of 40°. These are guides, not boundaries where reading, color or motion perception suddenly stops. Peripheral performance also depends on the size, contrast and motion of what you see. The dashed 40° line is a cinematic seating reference.
Can the same viewing angle feel different at different distances?
Yes. A 24-inch screen at 50 cm and a 120-inch screen at 2.5 m both span about 56° horizontally, but equal angular coverage does not guarantee the same sense of scale or presence. Screen distance, surrounding objects, head movement, sound and picture quality can contribute. A movie-viewing study found greater reported presence on a physically larger screen at the same angle in one experiment, but the effect was not statistically significant in a second. There is no established universal formula for a biologically corrected FOV or immersion score.
Specs shows two distance-related cues for ordinary screens: Optical focus stimulus is 1 ÷ distance in metres, in diopters (D); Eye convergence is the total angle needed to look at the screen centre, using illustrative 64 mm eye spacing. At 50 cm these are 2 D and 7.32°; at 2.5 m they are 0.4 D and 1.47°. They describe modelled viewing conditions, not your actual eye response, comfort or immersion. Glasses, age and individual vision affect the response; the entered distance is measured to the screen centre, including for curved screens.
On an ordinary 2D screen, focusing and convergence normally both refer to its surface. The vergence–accommodation conflict studied in stereoscopic displays is a different situation. VR headset optics also require their effective focal distance, rather than the physical distance to the tiny panel. We keep geometric FOV as angular coverage and show the distance cues separately.
See a screen at real size on your wall
On a supported iPhone or iPad, choose "See on your wall" beside the comparison, then select a display if you have more than one. You can also choose "View in AR" from a display's options menu. 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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