Design & Layout
Aspect Ratio Crop Calculator
Find the exact pixel or mm dimensions to crop an image to a specific aspect ratio — 16:9, 4:3, 1:1 square, A4, or a custom ratio — without distorting the content. Perfect for preparing images for print, social media and video.
Last updated: June 2026
Formula used
Crop width = Source width
Crop height = Source width × (ratio H / ratio W)
// Fit as tall as possible:
Crop height = Source height
Crop width = Source height × (ratio W / ratio H)
The calculator shows both "fit width" and "fit height" crops, and highlights the one that wastes less of the original image.
Example calculations
Example 1 — Crop 3000 × 2000 px to 16:9:
Fit width: 3000 × (9/16) = 1,688 px tall. Crop = 3000 × 1,688 px (156 px trimmed top/bottom).
Example 2 — Crop 4000 × 3000 px to A4 portrait (210:297):
Fit height: 3000 × (210/297) = 2,121 px wide. Result: 2,121 × 3,000 px.
How to use this calculator
- Enter your source image width and height in pixels.
- Select a preset ratio (16:9, 4:3, 1:1, A4, Letter) or enter a custom ratio.
- Read the resulting crop dimensions and the offset to centre the crop.
- Apply the crop in your image editor (Photoshop, GIMP, Canva, etc.).
Common aspect ratios
| Ratio | Use case | Decimal |
|---|---|---|
| 1:1 | Instagram square, profile photo | 1.000 |
| 4:3 | Standard photo, tablet | 1.333 |
| 3:2 | 35mm film, DSLR default | 1.500 |
| 16:9 | HD video, YouTube, TV | 1.778 |
| A4 (210:297) | European / ISO paper | 0.707 |
| Letter (8.5:11) | US paper | 0.773 |
Notes & limitations
This calculator computes the maximum crop that fits within the source dimensions without upscaling. It does not account for subject placement — always preview the crop in your editor. For coloring pages that need to fit A4 exactly, also check the A4 Print Size Calculator.
Frequently asked questions
How do I crop an image to 16:9 without distortion?
Use this calculator to get the exact pixel dimensions for a 16:9 crop from your source image. Then in your editor enter those exact dimensions for the crop tool.
What is the aspect ratio of A4 paper?
A4 has an aspect ratio of 1:√2 (approximately 1:1.414), meaning it is 210 × 297 mm. This ratio is special because two A4 sheets side-by-side give an A3 sheet with the same ratio.
How do I maintain aspect ratio when resizing?
When resizing in most editors, hold Shift or enable 'constrain proportions'. To crop to a specific ratio, use the crop tool with the ratio locked — this calculator gives you the exact numbers to enter.
What aspect ratio should I use for printing photos?
4:3 or 3:2 match standard photo print sizes. A4 uses a 1:√2 ratio. Square (1:1) is popular for Instagram. Check your print lab's required ratios before cropping.
Why does my image look stretched after cropping?
Stretching happens when you resize to new dimensions without maintaining the ratio. Always crop first to the correct ratio, then resize — never stretch a cropped image to fill a different ratio.