4:3 Aspect Ratio Calculator

Enter a known width or height to calculate the matching 4:3 dimension, then convert a diagonal screen size into physical width and height in inches.

Quick Facts

Formula
height = width x 3/4, or width = height x 4/3
4:3 means every 4 units of width pair with 3 units of height, e.g. 1024x768, 1600x1200, 800x600.
Diagonal split
width = diagonal x 0.8, height = diagonal x 0.6
Exact for 4:3 because 3-4-5 is a Pythagorean triple: the diagonal is 5 parts, width is 4 parts, height is 3 parts.

Your Results

Calculated
Calculated dimension
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The matching width or height
Full resolution
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Width x height, maintaining 4:3
Pixel diagonal
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sqrt(width^2 + height^2)
Physical size
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At your diagonal screen size

Ready

Enter a known width or height, then press Calculate.

About the 4:3 Aspect Ratio

The 4:3 aspect ratio describes a width-to-height relationship where the width is always 4/3 (about 1.333) times the height. It was the standard for television broadcasts and computer monitors before widescreen displays took over, and it is still used for some presentations, printed photos, and older projectors. Because the ratio is fixed, knowing just one dimension — width or height — is enough to calculate the other.

The formulas

Given a known width, the matching height is height = width x 3/4. Given a known height, the matching width is width = height x 4/3. Both formulas describe the same line: any point on it keeps width divided by height equal to exactly 4/3.

For a physical screen, the diagonal, width, and height form a right triangle. Because 3-4-5 is a Pythagorean triple, a 4:3 diagonal splits into exact fractions: width = diagonal x 4/5 and height = diagonal x 3/5. A 20 inch diagonal 4:3 screen is therefore 16 inches wide and 12 inches tall (16-12-20 is 4-3-5 scaled by 4).

Common aspect ratios

  • 16:9 — standard widescreen for HD/4K TVs, monitors, YouTube, most video content
  • 4:3 — older TVs and monitors; still used in some photography and presentations
  • 1:1 — square format; Instagram, profile photos
  • 9:16 — vertical (portrait) video; Instagram Reels, TikTok, YouTube Shorts
  • 21:9 — ultrawide monitor and cinematic format

Practical uses

  • Calculating the height of an image given a fixed width (or vice versa) without distortion
  • Cropping images to a target aspect ratio while maximizing pixel coverage
  • Ensuring video content dimensions match platform requirements before upload

Frequently Asked Questions

How do I calculate a 4:3 height from a width?
Multiply the width by 3/4 (0.75). For example, a width of 1024 pixels gives a height of 1024 x 0.75 = 768 pixels. To go the other way, multiply a known height by 4/3 (about 1.333) to get the matching width.
How do I find the physical width and height from a diagonal screen size?
For a 4:3 screen, the diagonal, width, and height form a 3-4-5 right triangle. Width equals the diagonal times 4/5 (0.8) and height equals the diagonal times 3/5 (0.6). A 24 inch diagonal 4:3 screen is 19.2 inches wide and 14.4 inches tall.
What are common 4:3 resolutions?
Standard 4:3 resolutions include 640x480 (VGA), 800x600 (SVGA), 1024x768 (XGA), 1400x1050 (SXGA+), and 1600x1200 (UXGA). Each divides evenly to a 4:3 ratio, for example 1600/1200 = 4/3.
How do I crop a widescreen image to 4:3 without distortion?
Do not stretch the image. Instead, keep the original pixel density and crop away pixels from the wider side until width divided by height equals 4/3, or add letterbox bars to the narrower side. Stretching to fit a 4:3 frame distorts circles into ovals and warps proportions.

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