How to resize an image and choose its output format

Resize, compress and format conversion are different jobs

Image dimensions are measured in pixels, such as 1200 × 800. File size is measured in KB or MB. The output format (JPEG, PNG or WebP) affects transparency, compatibility and compression, but it does not determine pixel dimensions on its own.

The main image workbench offers three Resize mode choices: Compress only, Resize only, and Resize and compress. Choose the mode based on whether a destination specifies dimensions, a file-size maximum, or both.

Step 1: choose the right resize mode

For a fixed width or height without a file-size restriction, select Resize only. The Target size field is intentionally ignored in this mode, so the resulting image is not guaranteed to fit below a KB limit.

For a limit such as 500 KB plus a dimension such as 800 pixels wide, choose Resize and compress, enter 500 in Target size, and set Target width (px) to 800. Choose Compress only if dimensions can stay as they are and you simply need a smaller file.

Step 2: enter width or height and protect proportions

Enter a Target width, Target height, or both. With Keep aspect ratio checked, entering only one dimension derives the other; entering both fits the image within the requested rectangle without stretching.

If your image is not already the destination's shape, preserving its aspect ratio may produce smaller dimensions than both requested values. The tool does not auto-crop to fill the rectangle. Unchecking Keep aspect ratio and forcing both values can visibly distort faces or logos, so inspect the distortion warning before proceeding.

The tool validates manual dimensions between 16 and 12,000 pixels, subject to a browser safety limit on total pixels. Some large combinations cannot be processed.

Step 3: select JPEG, PNG or WebP

Output format offers Auto recommended, JPEG, PNG and WebP. Auto recommended generally retains a safe supported format based on the source image; it is not a guarantee that another portal accepts that format.

Choose JPEG for photo-like images when the destination accepts it, but remember that JPEG does not preserve transparency. Choose PNG for transparent artwork or crisp graphics when size permits. WebP can offer efficient files, but some forms only accept JPEG or PNG.

Use the format that the receiving service explicitly requests; a smaller WebP is not useful when a form demands a JPG.

Step 4: check the plan, process and verify

Choose one JPEG, PNG or WebP source image under 50 MB. Before processing, check the Selected image panel for original dimensions, Planned output, Output format and Target. After processing, compare the Before and After previews and verify Dimensions, Output format, Target status and metadata handling.

Download the verified image and inspect it at the size where it will be used. If the target status is not a pass, do not assume the image meets the external service's requirements.

Worked example: resize a wide photo to 800 pixels

For a wide photo that only needs to be 800 pixels across, select Resize only, enter 800 in Target width, leave Target height blank, and keep Keep aspect ratio selected. The tool calculates the proportional height. Choose JPEG if the receiving service accepts it, process, and check the exported dimensions.

If the same form also says the image must be under 200 KB, choose Resize and compress, enter a Target size of 200 KB, then process. This adds the separate file-size check.

Troubleshooting incorrect dimensions or transparency

If the output does not exactly match both entered dimensions, check Keep aspect ratio. It fits rather than stretches when the original proportions differ. An exact crop must be prepared separately; this resize control does not crop.

If the background becomes opaque, check whether you explicitly selected JPEG. Use PNG or WebP where supported. If the KB target appears ignored, ensure you are not using Resize only.

If the image looks soft after shrinking, review whether the requested dimensions are unnecessarily small. Reprocess from the original rather than resaving an already degraded output.

Quick answers

Related tools

Keep learning