Preparing image dimensions in millimeters
How to use this tool
- Choose a JPEG, PNG, or WebP image.
- Enter dimensions and units. For physical sizes, choose the intended DPI.
- Choose the fit mode, resize, and verify the output dimensions.
Dimensions and proportions
Millimeters are useful for small print layouts. At 300 DPI, a 35 mm edge becomes approximately 413 pixels.
Physical size is a print setting
DPI here is used to calculate pixel dimensions. The downloaded image does not embed your chosen print DPI. Set that resolution in your printing software; the pixel count is the reliable output.
Understand the requested dimensions
Millimeters are useful when a layout describes small photographs, labels, or printed spaces with precise measurements. The measurement must still be converted to pixels for a digital file. Enter the required width and height in millimeters and choose the intended resolution, rather than interpreting those numbers as pixel counts.
A worked sizing example
The formula is millimeters ÷ 25.4 × DPI. A 35 × 45 mm image at 300 DPI needs about 413 × 531 pixels. A 40 mm edge at the same resolution is approximately 472 pixels. Rounding to whole pixels is necessary because a raster image cannot contain a fractional row or column.
| DPI used for calculation | Width in pixels | Height in pixels |
|---|---|---|
| 96 | 19 | 26 |
| 150 | 30 | 41 |
| 300 | 59 | 83 |
Contain, cover, and stretch
Contain scales the whole image to fit inside the output canvas. Any remaining space is white for JPEG and can be transparent for PNG or WebP. Cover fills the canvas and crops excess at the center. Stretch fills both dimensions independently, changing proportions when the source and output ratios differ.
These choices affect composition as well as dimensions. Cover is convenient for a uniform grid, but a centered crop does not know where your subject is. For careful framing, use the crop tool first and then resize the selected composition.
Tools for this step: Crop an image before resizing
Check the exported image
Small physical differences can matter in a measured layout. Verify whether the instructions use millimeters or centimeters before entering values; 35 mm and 35 cm differ by a factor of ten. Also check whether a border or margin belongs inside the requested measurement, since the resizer treats the whole canvas as the image size.
Read the width and height shown in the result and inspect the image at its intended viewing size. Making the file larger in pixels is not an enhancement process: it interpolates from the available information. Keep the source if a sharper or differently framed version may be needed later.
When the resized image is still too large in KB
Pixel dimensions and file size are separate measurements. The same-sized canvas can produce very different byte counts depending on its content, format, and quality. A lossless PNG of a detailed photo can remain large after resizing, while a simple flat graphic can be compact.
If the destination imposes both dimensions and a file-size ceiling, check both after the final operation. Target-size compression may reduce the dimensions further when quality adjustment is insufficient, so verify the final download rather than assuming an earlier resize guarantees compliance.
Tools for this step: Compress an image to a file-size target
Frequently asked questions
Is this tool free and unlimited?
Yes. It is free to use with no signup and no daily usage caps. You can process up to 20 files of up to 30MB each in one batch, then download your results.
Is the chosen DPI embedded in the image?
No. DPI is used to calculate pixel dimensions. The downloaded image does not carry that chosen print resolution as embedded metadata. Set the physical dimensions or resolution in your print software.
Will enlarging a small photo restore its detail?
No. Resizing can increase the number of pixels, but it cannot recover information missing from the source. Use a higher-resolution original when the enlarged result needs close inspection.
Does resize image in mm also guarantee an upload will be accepted?
No. This tool changes dimensions. The destination may have additional rules for file size, format, framing, background, or document content. Check those requirements against the final result.