Why can't quality alone get my image down to 50 KB?
A JPEG's size is roughly width × height × bits per pixel ÷ 8. The quality setting only changes the bits per pixel; the pixel count stays the same. A 4,000 × 3,000 phone photo has 12 million pixels, so even at a harsh 0.3 bits per pixel it still weighs about 450 KB. Reaching 50 KB would take 0.03 bits per pixel, far below the point where JPEG holds together: under roughly 0.3 bits per pixel you start to see 8 × 8 blocks, smeared color and halos around edges.
A quick check before you start: multiply your target in KB by 8,000 and divide by the number of pixels. Above about 1 bit per pixel, you can keep the dimensions at a comfortable quality. Between 0.3 and 1, lower the quality. Below 0.3, reduce the dimensions first, or the result will look broken.
How big is a JPEG at each size and quality?
Typical JPEG sizes for ordinary photos, estimated from about 0.6–1.2 bits per pixel at quality 70 (small images need more bits per pixel)
| Dimensions (pixels) | Megapixels | Quality 85 | Quality 70 | Quality 50 |
|---|---|---|---|---|
| 4,000 × 3,000 (phone camera) | 12 | 1.5–2.8 MB | 0.9–1.8 MB | 0.7–1.3 MB |
| 2,048 × 1,536 | 3.1 | 400–750 KB | 240–470 KB | 180–330 KB |
| 1,600 × 1,200 | 1.9 | 240–450 KB | 145–290 KB | 110–200 KB |
| 1,200 × 1,200 | 1.4 | 180–340 KB | 110–220 KB | 80–150 KB |
| 800 × 800 | 0.64 | 90–170 KB | 55–105 KB | 40–75 KB |
| 600 × 600 | 0.36 | 55–105 KB | 35–70 KB | 25–50 KB |
| 300 × 300 | 0.09 | 18–35 KB | 10–25 KB | 8–15 KB |
Detailed scenes (foliage, gravel, crowds, noisy low-light shots) land at the top of each range or above it; plain backgrounds, studio portraits and products on white land at the bottom. Screenshots and flat graphics follow different rules: see why PNG files get so large.
What pixel size fits each target?
Turn the formula around to get a pixel budget. At about 1 bit per pixel, which is what quality 65–75 gives an ordinary photo, each KB buys roughly 8,000 pixels:
Largest dimensions that usually fit each target as a JPEG at quality 65–75
| Target | Pixel budget | 4:3 photo | Square |
|---|---|---|---|
| 20 KB | about 160,000 | about 460 × 345 | about 400 × 400 |
| 50 KB | about 400,000 | about 730 × 550 | about 630 × 630 |
| 100 KB | about 800,000 | about 1,030 × 775 | about 900 × 900 |
| 200 KB | about 1.6 million | about 1,460 × 1,100 | about 1,260 × 1,260 |
| 500 KB | about 4 million | about 2,300 × 1,730 | about 2,000 × 2,000 |
| 1 MB | about 8 million | about 3,260 × 2,450 | about 2,830 × 2,830 |
Busy photos need about 20% fewer pixels for the same target; ID photos on a plain background fit more. If the site also states a pixel size, use that and let the quality do the rest.
How do I compress an image to an exact size?
The Fast WebP Converter compressor has a Target size mode built for this. You type a maximum in KB; it searches for the highest quality that fits, and if the image is still too big at a low quality, it scales the dimensions down step by step until it fits. Everything runs in your browser, so the image is never uploaded, and it is free for a single image with nothing to install.
- Open the page for your target: 20 KB, 50 KB, 100 KB, 200 KB, 500 KB, 1 MB or 2 MB. Each one opens with Target size already set. For any other number, open the compressor, switch to Target size and type it.
- Drop your image. JPG, PNG and WebP work in every browser; HEIC photos from an iPhone open in Safari.
- Pick the output format. Same as original keeps JPG as JPG and PNG as PNG; choose JPG when a form only accepts JPEG, which is also the easiest way to hit a small target with a photo.
- If the site requires specific dimensions (for example 600 px wide), turn on Limit width and type the width, so the tool only has to adjust the quality.
- Compress, check the size shown for the result, and download.
Which format hits a small target best: JPG, PNG or WebP?
For photos, JPG: every form accepts it and it compresses photos well. WebP is typically 25–35% smaller than JPEG at the same visual quality, so it fits more pixels into the same KB, but check that the site accepts .webp files first (WebP vs JPEG). PNG is the hardest to squeeze: the compressor shrinks it by reducing it to a palette of up to 256 colors, which works well for logos, signatures on white paper and screenshots, and poorly for photos.
What if the site also sets a minimum size?
Some portals give a range, such as 20–50 KB, or a floor such as 54 KB. If your file comes out under the minimum, start again from the original and choose a target near the top of the range, or keep more pixels. Compressing an already small file again will not make it bigger: when the tool cannot improve a file in its own format, it keeps the original. The photo and signature guide walks through typical form requirements.