How to Compress an Image to Any Size: The Complete Guide

"Reduce image size" means two different things, and confusing them is why people end up with a blurry photo that is still too big.

Dimensions versus file size

• Dimensions are pixels — 1920 × 1080. This is what a form means when it says "200 × 230 px".
• File size is kilobytes — how much disk the file occupies. This is what a form means by "under 50 KB".

They are related but not the same. You can halve the file size without touching the dimensions by compressing harder, and you can halve the dimensions without hitting a specific file size. Forms often specify both, and meeting one is not meeting the other.

Which target do you actually need?

Full range: all image size targets.

The method that works

Most tools give you a quality slider. The problem is that JPEG quality is not a file size — the same quality setting produces wildly different results depending on the picture. A flat product shot at quality 80 might be 40 KB; a detailed landscape at the same setting might be 400 KB.

So people do the search by hand: try 80, too big, try 50, too small, try 65. Each attempt re-compresses an already-compressed file, and quality degrades every round.

The reliable approach is to search automatically, always encoding from the original:

1. Encode at a mid-range quality and measure the actual bytes.
2. If it fits, remember it and try higher. If not, try lower.
3. Repeat about seven times, then keep the largest result that fits.

The difference is real. Asked for 20 KB, a fixed-quality tool commonly returns 8 KB — a pass, but you threw away more than half the quality you were entitled to. A proper search lands near 19 KB.

When compression is not enough

A 4000 × 3000 phone photo cannot reach 20 KB at any quality — too many pixels to describe. The only remaining lever is dimensions. Reducing to 800 × 600 first, then compressing, produces a far better-looking 20 KB file: fewer pixels, each described more accurately.

Need exact dimensions instead? 200 × 230 · 413 × 531 · 600 × 600 · 1080 × 1080 · any custom size.

Format decides more than you think

• JPEG — photographs. Far more efficient than PNG on anything with gradients.
• PNG — flat graphics, screenshots, transparency. Lossless, so quality settings do nothing; the only way to shrink it is fewer pixels or fewer colours.
• WebP — 25–35% smaller than JPEG at the same quality, but many upload forms still reject it.

The single most common trap: a photograph saved as PNG. It can be five times the size of the JPEG equivalent. If a photo will not get under a limit, check the format before blaming the compressor — PNG to JPG often solves it outright.

Other conversions: JPG to PNG · WebP to JPG · HEIC to JPG · JPG to WebP.

Three habits that ruin images

1. Compressing an already-compressed file. JPEG is lossy; damage accumulates. Always start from the original.
2. Ignoring the minimum. Ranges like 20–50 KB have a floor. A 6 KB file fails too.
3. Renaming the extension. Changing .png to .jpg does not change the format. Portals read the file header.