About the Aspect Ratio Calculator
Resizing an image or video without squashing it means keeping its aspect ratio constant — and this calculator does the proportional math for you. Enter the ratio you are working with (16:9 comes preloaded) and the width you need, and it instantly returns the exact matching height in pixels, rounded to whole numbers you can actually use in an export dialog or CSS.
It is a daily helper for video editors sizing exports, designers cutting thumbnails and banners, and developers reserving space for responsive media. Any ratio works: 4:3 for older footage, 1:1 for square posts, 9:16 for vertical stories, 21:9 for ultrawide, or the original pixel dimensions of a photo you want to scale. Free, instant, and nothing to install or upload.
Features
- Solves the missing dimension from any ratio
- Preloaded with 16:9 at 1920 px wide
- Accepts custom ratios like 4:3, 1:1 or 21:9
- Rounds to whole pixels for real exports
- Result updates live while you type
- No upload, account or install required
How to calculate aspect ratio dimensions
- Enter the ratio's width and height, e.g. 16 and 9.
- Type the target width you already know.
- Read the calculated height in pixels.
- Use both numbers in your export, crop or CSS.
Frequently asked questions
What is an aspect ratio?
An aspect ratio describes the proportional relationship between width and height, written as width:height. A 16:9 frame is 16 units wide for every 9 units tall regardless of actual size — 1920×1080 and 1280×720 are both 16:9. Keeping the ratio constant is what prevents stretching when you resize.
How do I calculate height from a width and a ratio?
Divide the width by the ratio: height = width ÷ (ratioWidth ÷ ratioHeight). For 16:9 at 1920 pixels wide, that is 1920 ÷ (16 ÷ 9) = 1080. This calculator performs that division for any ratio you enter and rounds the answer to whole pixels, ready to paste into an export or crop dialog.
What are the most common aspect ratios?
16:9 dominates video, YouTube and monitors; 4:3 covers older TV and many tablets; 1:1 is the square format for profile images and some social posts; 9:16 is vertical video for Stories, Reels and TikTok; 21:9 is cinematic ultrawide; and 3:2 is classic photography.
Can I use my image's own pixel size as the ratio?
Yes — that is often the easiest approach. Enter the original width and height, such as 4032 and 3024, directly as the ratio, then type your target width. The calculator returns the height that preserves the photo's exact proportions, no simplification of the ratio needed.
Why do resized images sometimes look stretched?
Stretching happens when width and height are scaled by different factors, breaking the original ratio — faces widen or thin noticeably at even 5% distortion. Calculating one dimension from the other, as this tool does, guarantees both scale identically so the content keeps its natural shape.