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Compress an image to 40 KB
To get an image under 40 KB, PixelFit aims at 40,000 bytes or less, so forms counting 1 KB as 1000 or 1024 bytes both accept it. Estimated from our measured encodes, that is about 455 × 341 pixels for a 4:3 photo at quality 75, or 485 × 605 for a portrait.
Under 40 KB
JPG · under 40 KB (at most 40,000 bytes) · original pixel size · white background
PixelFit aims at 40,000 bytes or less, so the file passes whether the form counts 1 KB as 1,000 or 1,024 bytes.
Fit, background and padding white background
Saving presets is part of Pro.
The result appears here: the exact byte count, pixel size and quality, the size before and after, a preview and a download button.
The batch kit (one ZIP for up to 500 photos, several photos merged into one PDF) is part of Pro.
What 40 KB means in bytes
40 KB is 40,960 bytes when 1 KB = 1024 bytes (40 × 1024) and 40,000 bytes when a server counts 1 KB = 1000 bytes. The 960-byte gap matters only near the limit. PixelFit aims at 40,000 bytes or less and prints the exact byte count, so you can compare it with the form.
40 KB is 0.039 MB; 256 such files fit in 10 MB. Uncompressed, the 455 × 341 photo that fits here would need 455 KB of raw pixels, so JPEG at quality 75 packs it about 12 to 1.
Largest pixel size that fits 40 KB
The biggest image of each kind, in its own aspect ratio, that stays at or below 40,000 bytes.
| Image | JPG q60 | JPG q75 | JPG q90 | WebP q75 |
|---|---|---|---|---|
| Head-and-shoulders portrait | 575 × 718 | 485 × 605 | 351 × 438 | 726 × 906 |
| Outdoor landscape (12 MP phone photo) | 527 × 395 | 455 × 341 | 353 × 264 | 484 × 363 |
| Scanned typed document page | 498 × 625 | 430 × 540 | 330 × 414 | 521 × 654 |
| Handwritten letter with signature | 970 × 797 | 800 × 657 | 551 × 452 | 1,268 × 1,042 |
| Flat-colour graphic (flag) | 1,569 × 1,098 | 1,338 × 936 | 986 × 690 | 2,279 × 1,595 |
A 12 MP phone photo at 40 KB
Our 12 MP landscape sample (4032 × 3024) is about 4.15 MB at quality 90, 109 times the 40 KB budget; even quality 30 leaves 1.26 MB (extrapolated from encodes up to 3,000 px). So the pixels must go down too.
At about quality 75 it fits 40 KB near 455 × 341 (0.16 MP, 1 % of the original pixels). Quality 60 allows 527 × 395; quality 90 needs 353 × 264.
JPEG quality for fixed pixel sizes under 40 KB
When a form fixes the pixels, only quality can move. Highest quality (of 100) that keeps each size at or under 40,000 bytes:
| Pixel size | Measured on | JPG | WebP |
|---|---|---|---|
| 200 × 230 (small ID photo) | portrait photo | quality 95+ (21.9 KB) | quality 95+ (17.4 KB) |
| 413 × 531 (35 × 45 mm at 300 DPI) | portrait photo | quality 83 (38.8 KB) | quality 90 (36.4 KB) |
| 600 × 600 (2 × 2 inch at 300 DPI) | portrait photo | quality 66 (38.8 KB) | quality 84 (37.8 KB) |
| 800 × 600 (4:3 web photo) | landscape photo | no: fewer pixels needed | no: fewer pixels needed |
| 1200 × 1600 (3:4 portrait upload) | portrait photo | no: fewer pixels needed | no: fewer pixels needed |
| 1240 × 1754 (A4 page at 150 DPI) | scanned typed page | no: fewer pixels needed | no: fewer pixels needed |
Measured JPEG files either side of 40 KB
Real encodes from our test set at quality 75: the largest file that stays under 40,000 bytes and the smallest that goes over.
| Image | Largest under 40 KB | Smallest over 40 KB |
|---|---|---|
| Head-and-shoulders portrait | 480 × 600: 39,317 B | 641 × 800: 60,900 B |
| Outdoor landscape (12 MP phone photo) | 400 × 300: 30,893 B | 500 × 375: 48,064 B |
| Scanned typed document page | 398 × 500: 34,663 B | 477 × 600: 48,445 B |
| Handwritten letter with signature | 800 × 658: 39,979 B | 1000 × 822: 59,731 B |
| Flat-colour graphic (flag) | 1200 × 840: 34,937 B | 1600 × 1120: 49,963 B |
JPG, WebP or PNG at 40 KB
At quality 75, WebP holds 484 × 363 of the landscape photo in 40 KB, JPG 455 × 341: 13 % more pixels. Portrait gain: 124 %. Typed page gain: 47 %. A moderate gain for the landscape photo at 40 KB, a large one for portraits: where WebP is accepted, use it for those. Many portals accept only JPG/JPEG, so this page starts in JPG.
A full-colour PNG is lossless, so its size follows the content. In 40 KB it holds a flat graphic of 871 × 609 pixels but a photo of only 162 × 121, against 455 × 341 as a quality-75 JPG. Reducing a PNG to a palette of up to 256 colours (PixelFit does this when a PNG must shrink) helps graphics far more than photos.
Which uploads fit comfortably in 40 KB
2 of the 6 sizes above keep quality 75 or better under 40 KB (200 × 230, 413 × 531); 3 miss even at quality 30 (800 × 600, 1200 × 1600, 1240 × 1754). At 455 × 341, quality 90 costs 64 % more bytes than quality 75.
A typed page reaches 498 × 625 at quality 60 in 40 KB, about 53 DPI if it is an A4 sheet.
How to compress an image to 40 KB
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Open the tool above
It is preset to 40 KB (40,000 bytes or less), JPG output.
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Add your image
Drop, paste or pick it; a PNG, WebP or (where the browser opens it) HEIC file becomes a JPG under 40 KB.
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Pixel size: only if asked
On auto, a typical photo stops near 455 × 341 at about quality 75.
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Download and check
name-40kb.jpg comes with its byte count, pixels and quality.
Sources
- Measured by PixelFit with sharp 0.35.5 / libvips 8.18.7 on 31 October 2026.
- Sample images, Wikimedia Commons, checked 31 October 2026: landscape (CC0 1.0) commons.wikimedia.org/w/index.php?curid=154070378; portrait commons.wikimedia.org/w/index.php?curid=23956389; typed page commons.wikimedia.org/w/index.php?curid=194775753; handwritten letter commons.wikimedia.org/w/index.php?curid=90423615; flag commons.wikimedia.org/w/index.php?curid=361734 (public domain).
- Binary prefixes, NIST, checked 31 October 2026: physics.nist.gov/cuu/Units/binary.html
Frequently asked questions
How do I compress an image to 40 KB?
Drop it into the tool here, preset to 40 KB. It searches JPEG quality (at most 8 encodes per pixel size), then scales pixels down if needed, until the file is 40,000 bytes or less. A 4:3 photo typically lands near 455 × 341 at about quality 75.
How do I compress an image to less than 40 KB without losing quality?
Give up pixels before quality: at quality 75, 40 KB holds 455 × 341 of a photo and 485 × 605 of a portrait; quality 90 at 455 × 341 costs 64 % more bytes.
Is 40 KB 40,000 or 40,960 bytes?
Both readings exist: 40,960 bytes (1 KB = 1024) or 40,000 bytes (1 KB = 1000). 40,000 bytes or less passes both.
Can I compress a PNG to 40 KB?
Yes, but a full-colour PNG photo stays big: about 162 × 121 pixels in 40 KB, versus 871 × 609 for a flat graphic. As a JPG the photo reaches 455 × 341.
What pixel size fits 40 KB?
At quality 75: a photo 455 × 341, a portrait 485 × 605, a typed page 430 × 540.
Related
Nearby file sizes
- Compress to 35 KB photo ≈ 426 × 319
- Compress to 30 KB photo ≈ 394 × 295
- Compress to 25 KB photo ≈ 357 × 267
- Compress to 45 KB photo ≈ 483 × 362
- Compress to 50 KB photo ≈ 510 × 382
- Compress to 60 KB photo ≈ 557 × 417
More ways to hit 40 KB
- JPG to PDF under 40 KB One image as a PDF
- Between 40 KB and 120 KB Minimum and maximum
- Image resizer with KB target Any size, pixels and format
Pixel sizes that fit 40 KB
- 25×35 mm photo about 30.6 KB as a quality-75 JPG
- 400×300 landscape about 30.2 KB as a quality-75 JPG
- 300×400 portrait about 30.2 KB as a quality-75 JPG
- 160×600 banner about 24.5 KB as a quality-75 JPG