Dimensions describe the pixel grid
A 4,000 × 2,500 image contains ten million pixels. Reducing it to 1,600 × 1,000 leaves 1.6 million pixels, which often reduces file size because the encoder has far less image data to describe.
- Width × height equals total pixels.
- Aspect ratio can remain unchanged while dimensions shrink.
File size depends on more than pixel count
Format, quality, transparency, noise, texture, and repeated detail all affect bytes. Two images with identical dimensions can have very different file sizes because a simple graphic compresses differently from detailed foliage or fabric.
- JPG and WebP quality settings trade bytes for fidelity.
- PNG can be efficient for flat graphics but large for photographs.
Match the change to the failed limit
Resize when pixel dimensions are excessive, compress when bytes are excessive, and convert only when the destination needs another format. Always compare the measured result with the original.