Image size in KB versus pixels
“Under 100 KB” and “600 × 600 pixels” describe different things. A photo may satisfy one requirement while failing the other.
Two measurements, two separate checks
| Measurement | What it means | Example |
|---|---|---|
| Pixels (px) | The number of image pixels across and down. | 600 × 600 px is a square image. |
| Kilobytes (KB) | The amount of storage used by the encoded file. | 100 KB in SizeKit means 100,000 bytes. |
| File format | The encoding used to store the image. | JPG and WebP are different formats. |
Two photos can have identical dimensions and very different file sizes. A detailed scene with leaves and hair usually takes more data to represent than a plain background at similar encoding settings. Format and compression quality also affect the number of bytes.
Example: a square photo under 100 KB
Suppose a form explicitly requests a 600 × 600 pixel JPG with a maximum file size of 100 KB. First prepare a square image. Then set both output dimensions to 600, select JPG, and use a 100 KB maximum. After processing, check the displayed dimensions and final file size before downloading.
Those values are an example, not a standard for passports, visas or job applications. Always use the destination’s current instructions. An official photograph can have requirements about framing, background or editing that a resizer cannot check.
Why keeping proportions matters
A photo that is 1600 pixels wide and 1067 pixels high is not square. With proportions locked, reducing its width to 800 gives a height of about 534 pixels. That preserves the original shape.
Forcing the same photo into 600 × 600 pixels without cropping changes its shape and can stretch a face. SizeKit has no crop control. Crop to the required aspect ratio in your photo editor first, then resize the cropped image here. Turning proportions off is appropriate only when you intentionally want to change the shape.
Choose what to change
- Correct dimensions, too many KB: keep the dimensions and lower the maximum file size. Preview the result because compression can remove detail.
- Too many pixels, acceptable KB: reduce the dimensions. The file will be re-encoded, so check its size again.
- Both are too large: set the required dimensions and the KB limit together.
- The result is too blurry: use a higher permitted size limit or start with a clearer source. Enlarging a low-resolution image does not restore missing detail.
Pixels are not centimetres or print resolution
A width measured in centimetres describes a physical print. Converting it to pixels requires a pixels-per-inch assumption. For an online form, use explicit pixel dimensions whenever they are provided. SizeKit controls pixel dimensions and file size; it does not provide a print-resolution metadata setting.
Keep the original photo. Repeatedly compressing an already compressed copy can reduce quality further. If you need a different result, start again from the original.