How this instrument works
An aspect ratio is a rectangle's width measured against its height, reduced to the smallest whole numbers that produce the same shape. A 1024×768 monitor and a 640×480 one look proportionally identical once each is divided by its own greatest common divisor (GCD), even though the newer panel has more than three times the pixels — which is exactly how a decades-old VGA display and a mid-2000s office monitor both end up labelled '4:3.'
4:3 (also written 1.33:1) was the standard shape for film and television cameras from the earliest motion-picture equipment through the analog NTSC and PAL broadcast era, and computer monitors carried the same shape through the CRT years and into early flat panels. Familiar 4:3 resolutions include 640×480 (VGA), 800×600 (SVGA) and 1024×768 (XGA).
4:3 faded from dominance once widescreen 16:9 became the broadcast and computing default during the 2000s and 2010s, but it hasn't disappeared. It survives in classic film-camera formats, retro and pixel-art design work, and any legacy hardware or software originally built around a near-square canvas — plus plenty of nostalgia among people who grew up with 'fullscreen' television.
- Enter your screen or image's pixel width into Width (px) — for example 1024 for an XGA display.
- Enter the matching pixel height into Height (px) — for example 768.
- Read the simplified ratio directly beneath the inputs; a genuine 4:3 frame reduces to exactly 4:3.
- If your numbers reduce to something else, like 16:9 or 3:2, your source isn't a classic 4:3 shape — try the general Aspect Ratio instrument to identify its actual proportions.
Worked example — XGA at 1024×768
Enter 1024 into Width (px) and 768 into Height (px) — the pixel grid of an XGA-era CRT or early LCD monitor. The greatest common divisor of 1024 and 768 is 256, so dividing both by 256 gives a ratio width of 4 and a ratio height of 3. Simplified ratio reads 4:3.
The same shape appears at 800×600 (SVGA, GCD 200) and 640×480 (VGA, GCD 160, the original IBM PC/AT-era standard) — three resolutions spanning decades of hardware that all describe the identical boxy proportions.
Questions
What is the 4:3 aspect ratio used for today?
4:3 still shows up in classic photography formats, retro and pixel-art design, presentation slides converted from older templates, and any legacy hardware or software built around a near-square canvas. It's no longer the default for TVs, monitors or video, but plenty of archival and nostalgic content is still natively 4:3.
Why did TVs and monitors switch away from 4:3?
Widescreen 16:9 became the standard during the shift to HDTV broadcast because it better matches how cinema had long been filmed and gives a wider field of view for video. Once broadcasters, camera makers and display manufacturers standardised on 16:9, computer monitors followed the same shape through the 2000s and 2010s, leaving 4:3 as a legacy format.
What resolutions are 4:3?
Common 4:3 resolutions include 640×480 (VGA), 800×600 (SVGA), 1024×768 (XGA) and 1600×1200 (UXGA). Each of these reduces to exactly 4:3 through this instrument's greatest-common-divisor method — for example, 1024÷256=4 and 768÷256=3, since their GCD is 256.
Is 4:3 the same as 'fullscreen'?
Yes — 'fullscreen' is the common name for the 4:3 (1.33:1) aspect ratio of early standard television screens and computer monitors, as opposed to 'widescreen' 16:9. The two terms describe the same shape; 'fullscreen' is simply the everyday label people used before widescreen became the default.
How do I convert a 4:3 image to fit a widescreen frame?
You generally have to crop the sides of the widescreen frame, add letterbox bars on the left and right of the 4:3 image, or stretch the image and accept some distortion — there's no way to fill a 16:9 frame with unmodified 4:3 content, since the two shapes have genuinely different proportions rather than one being a scaled version of the other.