Calculation methodology
How Screen Size Comparison calculates display dimensions
Last reviewed: August 9, 2026
A diagonal alone does not tell you how much wall or desk space a display needs. This site converts the diagonal and aspect ratio into the viewable panel width, height, and area, then uses those values to draw both screens at the same scale.
The calculations are deterministic: the same inputs always produce the same result. They describe the active rectangular panel, not a product’s bezel, stand, curve, hinge, speaker housing, or shipping dimensions.
width = diagonal x ratio width / sqrt(ratio width^2 + ratio height^2)
height = diagonal x ratio height / sqrt(ratio width^2 + ratio height^2)
visible area = width x height
The width and height formula
For a diagonal d and an aspect ratio a:b, the panel width is d × a ÷ √(a² + b²), and the panel height is d × b ÷ √(a² + b²). This is the Pythagorean theorem rearranged for a rectangle. For example, a 55-inch 16:9 panel is about 47.9 inches wide and 27.0 inches high before any bezel is added.
Area and percentage differences
Visible area is width multiplied by height. The percentage shown on a comparison page is calculated against the first display, so changing the order can change the wording and sign even though the physical panels remain the same. Area is useful for judging the scale of an upgrade, while width and height are the better numbers for furniture, wall, and desk fit.
Units, precision, and rounding
Calculations use full floating-point precision internally. Display values are normally rounded to one or two decimal places so the result stays readable. Centimetres are converted using exactly 2.54 centimetres per inch. Small differences caused by rounding should not be treated as manufacturing tolerances or proof that a retailer’s listing is wrong.
How the visual overlay is scaled
Both rectangles are drawn from the calculated width and height using one shared scale factor. The scale is reduced only when needed to fit the available browser space, so the relationship between the two displays remains unchanged. It is a relative visual reference, not a life-size ruler unless the browser and physical display have been calibrated separately.
Limits of a mathematical comparison
A screen-size result cannot replace the manufacturer’s specification sheet. Curved monitors are treated as flat rectangles, advertised diagonals may be rounded, and usable area can differ around notches or rounded corners. Product width also depends on the bezel, chassis, stand, speakers, and mounting hardware. Before buying, compare the result with the current manufacturer dimensions and measure the actual installation space.
Independent maintenance and review
Screen Size Comparison is an independently maintained utility and is not a display manufacturer, retailer, or testing laboratory. Formula changes are checked against known rectangular examples, and representative pages are reviewed after changes to calculations or rendering. Explanatory copy is updated when a result is unclear, a device convention changes, or a limitation needs to be stated more directly.