Screen-dimension calculator
Work out a screen's actual width and height from its diagonal size and aspect ratio — useful for checking whether it will physically fit a space before buying.
Result
Width
Height
Width
Height
How to use this tool
- Enter the screen's diagonal size, as quoted in the spec sheet.
- Choose its aspect ratio.
- Read the actual width and height.
Assumptions
- Assumes the screen is a perfect rectangle at exactly the stated aspect ratio.
Technical details: what the fields mean
- Screen diagonal
diagonalInches - Diagonal screen size, as usually quoted in product listings (e.g. '55-inch TV').
- Aspect ratio
aspectRatio - The screen's width-to-height ratio — 16:9 is standard for most modern TVs and monitors, 21:9 for ultrawide monitors, 4:3 for older screens.
Methodology
Height = diagonal ÷ √(ratio² + 1). Width = height × ratio — derived from the Pythagorean relationship between width, height and diagonal.
Worked example
55-inch, 16:9 screen
Inputs: Screen diagonal: 55 in, Aspect ratio: 16:9
Result: 47.94in × 26.96in (121.8 × 68.5cm) for the picture area.
Will a 65-inch TV fit a 150cm-wide alcove?
Inputs: Screen diagonal: 65 in, Aspect ratio: 16:9
Result: 143.9cm wide — only about 6cm to spare before adding the frame, so check the model's full width on its spec sheet.
34-inch ultrawide monitor sold as 21:9
Inputs: Screen diagonal: 34 in, Aspect ratio: 21:9
Result: 31.25 × 13.39in (79.4 × 34.0cm). Most 34-inch ultrawides are actually 64:27 (3440×1440), which is 79.6 × 33.6cm — within a few millimetres.
27-inch 16:9 monitor on a desk
Inputs: Screen diagonal: 27 in, Aspect ratio: 16:9
Result: 23.53 × 13.24in (59.8 × 33.6cm).
Practical guidance
- Measure the actual space (shelf, wall mount, cabinet) using the calculated width and height, not just the diagonal figure, before buying a screen.
- The result is the picture area; frames typically add a little on each side, and stands add height and depth — the manufacturer's spec sheet lists the overall size.
- Switching from 16:9 to 21:9 at the same diagonal gives a wider but much shorter screen.
Common mistakes
- Assuming the diagonal size alone tells you whether a screen fits a space — two screens with the same diagonal but different aspect ratios have different actual widths and heights.
FAQs
How wide is a 55-inch TV?
About 47.9 inches (121.8cm) wide and 27.0 inches (68.5cm) tall for the picture, assuming the standard 16:9 ratio.
How wide is a 65-inch TV in cm?
About 143.9cm wide and 80.9cm tall for the picture area, plus the frame.
Last reviewed: 2026-09-25
A geometric calculation from the stated diagonal and ratio only — doesn't include the bezel/frame width, which adds a little to the overall physical size.
This tool provides an indicative estimate, based on the assumptions stated above.
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