Image proportions, borders, and crop dimensions
Fit mode reports the borders needed around the resized image. Fill mode reports how much of the resized image is cropped from each side. The source ratio is reduced to its smallest whole-number pair.
For a physical print of the resized image, the Print Size Calculator converts pixels to inches and centimetres at a chosen PPI.
The formula
Multiply each source dimension by the selected scale. Fit dimensions round down to stay inside the frame; fill dimensions round up to cover it. Half the difference on each axis gives a centred border or crop. One-pixel minimums prevent an unusable zero-sized dimension.
Worked example
A 4,000 by 3,000 image has a 4:3 ratio. Inside a 1,920 by 1,080 frame, fit mode gives 1,440 by 1,080 with 240-pixel borders on each side. Fill mode gives 1,920 by 1,440 and crops 180 pixels from the top and bottom. A 4,000 × 3,000 image fills a 1,920 × 1,080 frame at 1,920 × 1,440 pixels. It crops 180 pixels at each vertical edge and removes 25% of the resized image area.
How to use this calculator
- Enter the source width and height in whole pixels.
- Choose a preset frame or enter custom target dimensions, then select fit or fill.
- Read both ratios, resized dimensions, border/crop per edge and cropped-area percentage.
Use crop amounts after resizing
The reported crop is measured on the resized image, not on the original pixel grid. Set the resize dimensions first, then crop to the target frame. The calculation assumes a centred subject; portraits or off-centre compositions may need the crop shifted manually.
Integer pixels and proportional scaling
Most digital exports use whole pixels. Rounding can change the exact aspect ratio slightly, especially for very small outputs or extreme shapes. A half-pixel border result means the extra pixel must go on one side when constructing a raster canvas. Increasing dimensions enlarges the image but does not establish that enough source detail exists for the intended use.
Choosing a frame and seeing the tradeoff
Presets supply a 1,920 × 1,080 landscape, 1,080 × 1,080 square, or 1,080 × 1,920 portrait frame. Custom dimensions stay saved when you choose a preset. Fit rounds the unconstrained dimension downward, with a minimum of one pixel; fill rounds it upward. Cropped area is one minus target area divided by the rounded resized area for fill, and zero for fit. Axis scales can differ slightly because of whole-pixel rounding; no actual image file is edited.
Assumptions & limitations
What this calculation assumes
- Square pixels, no rotation, and a centred frame treatment.
What to keep in mind
- Computes dimensions only; it does not crop or resize an uploaded image.
- Does not upload, resize, crop, or export an image file.
Common questions
Which mode avoids cutting off the subject?
Fit keeps the full image and may leave borders. Fill removes excess content whenever source and target ratios differ.
Why are two borders sometimes unequal in an editor?
An odd total difference cannot be divided into two equal whole-pixel borders. Put the remaining pixel on either side.
Sources & further reading
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