Resizing Images Without Distortion: Aspect Ratio Math
October 21, 2026
To resize an image without distortion, keep the ratio of width to height constant. New height = new width × (original height ÷ original width). For a 4000 × 3000 photo, the ratio is 4:3, so scaling to 1,200 pixels wide gives a height of 1,200 × 3,000 ÷ 4,000 = 900 pixels. Choose either the width or the height, and let the other follow.
Skip the math and get your answer instantly:
Open the Aspect Ratio Calculator →The Formula in Practice
Reducing a 1920 × 1080 video frame (16:9) to 1,280 wide gives 1,280 × 1,080 ÷ 1,920 = 720 pixels high. Going the other way, if a layout needs 600 pixels of height for a 3:2 photo, the width is 600 × 3 ÷ 2 = 900.
If the result is not a whole number, round it and accept a tiny change in ratio, or crop a pixel or two. Rounding by one pixel is not visible.
Common Aspect Ratios
Different media standardized on different ratios. Matching the destination avoids black bars or cropped content.
| Ratio | Typical use | Example size |
|---|---|---|
| 16:9 | Widescreen video, YouTube | 1920 × 1080 |
| 9:16 | Vertical video, stories, reels | 1080 × 1920 |
| 1:1 | Square social posts | 1080 × 1080 |
| 4:5 | Portrait social posts | 1080 × 1350 |
| 3:2 | 35 mm photography | 6000 × 4000 |
| 4:3 | Older TVs, many compact cameras | 4000 × 3000 |
| 21:9 | Ultrawide video and monitors | 2560 × 1080 |
Cropping vs. Stretching
When the target ratio differs from the original, you have two choices: crop to the new ratio or add padding, called letterboxing or pillarboxing. Do not stretch, which distorts faces and shapes.
To crop a 16:9 image to 1:1, keep a square equal to the height: 1,080 × 1,080 from a 1920 × 1080 frame, discarding 840 pixels of width. Check that the important content survives the crop, or use a different framing.
Resolution and File Size
Reducing dimensions reduces file size roughly in proportion to the pixel count. Halving both width and height cuts pixels to a quarter. Avoid enlarging beyond the original size, which adds no detail and tends to look soft.
Frequently Asked Questions
How do I find the height for a new width?
Multiply the new width by the original height divided by the original width.
What is the aspect ratio of 1920x1080?
16:9.
How do I convert 16:9 to a square?
Crop to the shorter side. From 1920 × 1080 that is 1080 × 1080.
Why does my image look stretched?
The width and height were resized by different factors. Lock the aspect ratio when scaling.