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Aspect Ratio Calculator online

Scale dimensions while maintaining aspect ratios — for images and video

Aspect Ratio Calculator logo
by
CHUNKY
MUNSTER
// From dimensions → get ratio
× =
16:9
// Scale with ratio
×
// Common aspect ratios: 16:9 (video/HD) · 4:3 (classic TV) · 1:1 (square) · 9:16 (portrait video) · 2.35:1 (widescreen) · 3:2 (photography) · 21:9 (ultrawide)

How to Use aspect-ratio-calculator

  1. Enter the width and height of your source media in the input fields.
  2. The tool calculates the simplified ratio (e.g. 16:9, 4:3) and the GCD.
  3. Enter a new width (or height) in the scale section to get the proportional dimension.
  4. Use the presets panel to jump to common ratios: 16:9, 4:3, 1:1, 21:9.

Maintaining aspect ratio when scaling images or video prevents distortion — a 1920×1080 frame scaled to 1280 width must be 720 pixels tall, not 900. This calculator finds the simplified ratio of any resolution, scales dimensions proportionally, and lets you verify that a crop or resize will not change the original proportions.

Common Aspect Ratios Reference

16:9 is the standard widescreen ratio for HD and 4K video, YouTube, and most monitors. 4:3 was the original television and early computer monitor standard. 1:1 is used for Instagram square posts and profile pictures. 21:9 (ultrawide) is common in cinema and ultrawide monitors. 9:16 is the portrait equivalent of 16:9, used for TikTok, Instagram Stories, and Reels. The calculator handles any arbitrary resolution, not just these presets.

Frequently Asked Questions

What does "simplified" ratio mean?

3840×2160 simplifies to 16:9 by dividing both values by their greatest common divisor (480). Simplified ratios make comparisons easier — any 16:9 resolution simplifies to 16:9.

Why is 1920×1080 called "16:9" when 1920÷16=120 and 1080÷9=120?

Both 1920 and 1080 are divisible by 120. Dividing both by 120 gives 16:9. The GCD of 1920 and 1080 is 120.

How do I find the height for a 1280-wide 16:9 image?

Divide 1280 by 16 to get one unit (80), then multiply by 9: 80 × 9 = 720. Or use the scale section of this calculator — enter the known dimension and it computes the other.

What ratio does a 4K cinema frame use?

DCI 4K is 4096×2160, which simplifies to 256:135 — slightly wider than 16:9. Consumer 4K (UHD) is 3840×2160 = 16:9.

Pair this with the Aspect Ratio Resizer to compute precise dimensions for any scaling operation.