Screen Size Calculator — Width, Height and Area

Screens are sold by one number — the diagonal — and used in two: the width and height that must fit your desk, wall, dashboard or hand, every single day. Give this calculator a diagonal and an aspect ratio, and it returns the true width, height and area of the panel; add the resolution and it prices the sharpness in pixels per inch as well.

Pythagoras Sells Televisions and Monitors

The diagonal convention survives because it flatters twice: it is the largest single number a rectangle owns, and it conceals how much the shape matters. The undoing is one theorem: with the aspect ratio a:b, a scaling factor divides the diagonal in the ratio’s proportions — width = d × a ÷ √(a² + b²), height = d × b ÷ √(a² + b²) — and the area follows. Run the same 55 inches through the selector’s shapes and watch the object’s identity change: the 16:9 default yields about 47.9 × 27.0 inches and 1,293 square inches of picture; the 21:9 yields about 50.6 × 21.7 and only 1,095 square inches (about a sixth less screen wearing the same badge); the venerable 4:3 yields 44 × 33 and the largest area of the three. Diagonal is a length; a screen is an area. This calculator is the translation between the marketing unit and the physical one, for TVs, monitors, tablets, phones and projector throws alike.

Worked Example: The 55-Inch Living-Room Standard Screen

The defaults price the world’s commonest big screen: 55 inches, 16:9, with a 3840-pixel (4K UHD) resolution entered for sharpness. Width = 55 × 16 ÷ √337 ≈ 47.9 inches (121.7 cm); height = 55 × 9 ÷ √337 ≈ 27.0 inches (68.5 cm); viewable area ≈ 1,293 sq in. The PPI line resolves to 3840 ÷ 47.9 ≈ 80 pixels per inch — a figure that sounds low beside a phone’s 400+ until viewing distance enters (the TV page of this hub takes up exactly that thread): at living-room distances 80 PPI sits well inside the eye’s resolving limit, which is why 4K televisions are not a scam and 8K ones mostly are. Every number in the example is one the diagonal alone kept hidden.

Area: The Comparison the Diagonal Quietly Forbids

Because area scales with the square of the diagonal within a shape, and shrinks as the shape widens at a fixed diagonal, the honest cross-shopping unit is square inches (or cm²), and the calculator prints it for exactly that purpose. The canonical trap is the ultrawide “upgrade”: a 34-inch 21:9 monitor advertises four diagonal inches over a 27-inch 16:9, while its area (about 419 vs 311 sq in, a 35% gain) tells the true, more modest story — and its height is actually smaller (13.4 vs 13.2 — nearly identical, the width carrying the whole difference), which matters for documents and code. Phones play the same trick across generations: taller aspects inflate diagonals while widths — the dimension thumbs and pockets feel — barely move. Measure in area and height, buy in area and height; let the diagonal be the label it is.

The Class System: “55-Inch Class” and Other Honest Fudges

Product categories tolerate a rounding the calculator does not: panels are sold in classes — a “55-inch class” television may measure 54.6 inches on the diagonal, a “27-inch class” monitor 27.0 or 26.9 — with the true viewable figure buried in the specification sheet. The discrepancy is small (a percent or two) but it is exactly the size that matters at the end of this page’s arithmetic: cabinet openings, VESA-and-stand footprints and the width your media wall was built around. Use this calculator with the actual viewable diagonal from the spec sheet where the fit is tight, and with the class number where only the class of purchase is being chosen. Knowing which of the two questions you are answering is most of measurement literacy, in screens as in freight.

Resolution’s Partner: Viewing Distance Closes the Loop

The PPI line in this calculator opens a question it deliberately leaves to its sibling page: sharpness is a relationship between pixel pitch and the eye’s angle at your seat, so the same 80 PPI that is invisible at three metres is coarse at thirty centimetres (a desktop monitor’s 27-inch 4K panel runs about 163 PPI for exactly that reason, and its 1440p sibling about 109). The practical chain for a purchase runs: this page for the panel’s true dimensions and PPI, the TV-size page for the distance those figures must serve, and the area comparison for honesty between candidates. Diagonal, the salesman will note, appears in none of the three steps except as raw material — which is the calculator’s quiet thesis about how screens ought to be bought.

Curved and Odd Shapes: Where the Rectangle Ends

Two modern wrinkles bend this page’s clean geometry without breaking it. Curved monitors quote their diagonal along the panel’s arc-chord conventions of the manufacturer while their desk footprint follows the chord — the calculator’s width, from the flat formula, approximates the chord closely at the gentle curvatures sold (1000R–1800R), and errs politely; measure the furniture gap against the product drawing as the class section counsels. Foldable phones quote two diagonals (folded and open) for one device whose open aspect this calculator prices like any other once the open diagonal and ratio are entered. The theorem survives both fashions, because a screen, however it bends or folds, is sold flat in the catalogue — and measured, by this page, exactly as bought.

Related Tools

More from the Other Calculators hub: the TV Size Calculator for viewing distance from these dimensions, and the PPI Calculator for a deeper sharpness audit.

Frequently Asked Questions

How wide is a 55-inch TV, really?

The viewable picture of a 55-inch 16:9 screen is about 47.9 inches wide and 27.0 high — the worked example. The television product is wider by its bezels (usually a few tenths of an inch per side on modern sets, more on older ones) and its stand’s footprint is a separate, deeper measurement. For wall mounting and cabinet fit, the calculator’s panel figures are the floor, the manufacturer’s full-dimension drawing is the authority, and the gap between them has embarrassed many alcoves, media walls and delivery crews over the years.

Why do two screens with the same diagonal have different sizes?

Aspect ratio. The diagonal is one number shared by a family of rectangles, and widening the shape at fixed diagonal trades height for width and surrenders area (a circle has the most area for its diameter; screens move away from squareness in one direction only). This is why the calculator’s second input exists: diagonal without aspect is an underdetermined problem, and any answer given without it has silently assumed 16:9 — an assumption that fails for ultrawides, tablets, phones and every older 4:3 panel still in service.

What is PPI and how much do I need?

One sentence of summary before the detail: PPI is the count of pixels along one inch of the panel, and the amount you need is set entirely by the distance between the panel and your eyes.

What is PPI in fuller detail, then?

Pixels per inch — the resolution laid along the screen’s width (this calculator’s version, with the vertical figure matching at square pixels). Need is distance’s function: at phone distances (25–30 cm) the eye resolves up to roughly 300–460 PPI; at laptop distances about 200; at TV distances 60–100 suffices, as the worked example’s 80 PPI shows. Beyond the resolving limit at your distance, extra PPI buys nothing visible — which reframes the 8K question as a question about how close you sit, answerable with the TV-size tools rather than with showroom awe.

How are phone screen sizes measured?

The same diagonal, with two modern wrinkles: the quoted figure spans the full rectangle the panel would occupy including its rounded corners, and tall aspects (19.5:9, 20:9) inflate it against the phone’s actual width, which has stayed near 70–75 mm across a decade of growing “sizes”. Enter the phone’s aspect from the selector and the calculator returns the honest width to compare against your hand and pocket. Notches and camera cutouts subtract a sliver of area the diagonal never mentions.

What diagonal do I need for a given width — say, a 60-inch-wide space?

Run the formula backwards (or run this calculator twice): for 16:9, width = 0.8716 × diagonal, so a 60-inch width means a diagonal of 60 ÷ 0.8716 ≈ 68.8 inches — a 70-inch-class screen, before bezels. The backward question is the cabinet-maker’s and the media-wall designer’s, and it is why the factors are worth printing: 16:9 width is 87.16% of diagonal and height 49.03%; 4:3’s are 80% and 60%; 21:9’s are 91.9% and 39.4%. With the pair for your aspect in hand, any space converts to a screen class in one division, and any screen class converts back to its true footprint the same way.

Are projector “screens” measured the same way?

Identically — diagonal of the viewable image area, same aspect arithmetic — with throw distance joining the problem (the projector’s throw ratio converts distance to image diagonal, which this calculator then decomposes). The projector-specific traps are ambient-light washout (an area problem: the same lumens spread over more square inches dim) and the screen material’s border, the bezels of that world. The geometry, though, is the geometry: Pythagoras runs the cinema too.