IZN Tools

Image File Size Calculator

Estimate the output size before you commit to a format and quality.

Megapixels2.1
JPEG1.40 MB – 2.80 MB
WEBP1007.89 KB – 1.97 MB
AVIF667.20 KB – 1.30 MB
PNG4.43 MB – 8.86 MB
Estimates from typical photographs — actual size depends heavily on content, and flat artwork compresses far better
Computed on this device
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What actually drives the size

In order of effect:

  1. Dimensions. Bytes scale with pixel count, so halving the width quarters the area. This is the biggest lever by a distance.
  2. Format. AVIF beats WebP beats JPEG at the same visual quality, often by 25–35% each step.
  3. Quality setting. Real but non-linear — the step from 95 to 85 is nearly free, and 60 to 50 is where artefacts appear.
  4. Content. Noise, foliage and texture are expensive; flat backgrounds and soft gradients are cheap.

Bits per pixel is the honest measure

Divide the file size in bits by the pixel count and formats become comparable. Well-compressed web photography lands somewhere around 0.5–2 bits per pixel. Below 0.4 you should expect visible blocking; above 8 the file is much larger than it needs to be.

The quality analyzer reports that figure for a real file, which is the check to run once the image exists.

Plan dimensions first

Deciding "1600 px wide as WebP at 80" before exporting is worth more than any amount of tuning afterwards. Getting the dimensions right removes the problem; adjusting quality only trims around it.

Questions

How accurate is the estimate?+

It is a range, not a number, and it is derived from typical photographs. Content dominates: a portrait against a plain wall compresses several times better than a forest at the same dimensions. Use it to compare formats and sizes, not to predict a byte count.

Why is PNG shown as a flat figure?+

Because PNG is lossless — quality has no effect on it, only dimensions and content do. The figure assumes photographic content, which is PNG's worst case; a flat graphic will be far smaller.

What is a reasonable target?+

For a full-width hero on a web page, under 200 KB. For an in-article image, under 100 KB. If the estimate is far above that, the dimensions are usually the problem rather than the quality setting.

Should I just export and measure?+

If you have the image, yes — that is exact, and the [image compressor](/t/image-compressor) shows the real numbers. This is for deciding dimensions and format before the image exists.