Crop Ratio Calculator

What this generator does

Finds the largest whole multiple of your ratio that fits inside the image, giving a crop whose sides are exact multiples rather than approximately right. It then centres that box and reports the offset and the share of the original area retained.

How to use this tool

1. Enter the pixel size of your image.
2. Enter the ratio you want, as two numbers such as 16 and 9.
3. Read the crop size and the offset that centres it.
4. Check the area kept before deciding the crop is acceptable.

Understanding the controls

Source width and height

The image being cropped, in pixels. Both matter here — unlike a pure ratio calculation, the answer is in real pixels.

Target ratio

Two whole numbers such as 16 and 9, or 4 and 5. Reducing them first (6:4 rather than 3:2) makes no difference to the answer.

Common use cases

• Finding the largest square crop a photo will allow
• Preparing an image for a fixed-ratio slot without guessing
• Seeing how much of a photo a demanding ratio would discard
• Getting exact crop coordinates for a script or an editor
• Comparing two candidate ratios by how much each keeps

How this generator works

The largest crop is found by asking how many times the ratio fits across the width and how many times down the height, and taking the smaller of the two. Multiplying that scale by each side of the ratio gives a box that is exactly the requested shape by construction. Before display the crop is confirmed to be a whole multiple of both ratio parts, to sit entirely inside the image, and to be maximal — one step larger is checked and must not fit.

Randomness and fairness

Nothing here is random. The same image size and ratio always give the same crop.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

• The crop is centred, which is the right default and the wrong choice whenever the subject is not in the middle — the offset is given so you can move it.
• Only whole-pixel crops of the exact ratio are returned, so an image whose size shares no useful factor with the ratio may lose a pixel or two more than strictly necessary.
• Enlarging is never considered: this only ever crops, so a ratio the image cannot fill stays uncropped in that direction.
• Content-aware cropping, faces and rule-of-thirds placement are all outside what a ratio calculation can know.

Privacy and your data

Nothing is uploaded and nothing leaves your browser. The dimensions you enter are not stored or included in analytics.