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How do I compress an image to under 300KB?
To compress an image to under 300KB, resize it to about 1,800 pixels on the long side or to the size it will be displayed at, then compress with a 300KB target so quality drops only as far as needed. A 1920 × 1080 image usually fits at good quality; a full 12-megapixel photo does not.
300KB at a glance
- Exact limit: 300KB is 307,200 bytes, since the compressor counts 1KB as 1,024 bytes.
- Strict limit of 300,000 bytes: set the target to 292 instead.
- Balanced-quality pixel budget (about 1 bit per pixel): 2.5 megapixels, roughly 1810 × 1350.
- A Full HD frame (1920 × 1080) gets 1.2 bits per pixel. It fits at balanced quality.
- A 12-megapixel phone photo at full size gets 0.20 bits per pixel. That is too tight for a clean result, so resize first.
What 300KB is a good size for
300KB is a web-publishing size. It suits a full-width hero or banner, the featured image on a blog post, or a large gallery photo: places where the image is the main thing on screen and looking sharp matters more than shaving off the last few kilobytes.
It also appears as an upload limit on some forms that accept photos of documents or of goods, such as claims, warranty or marketplace forms, where the person reviewing the upload needs to see real detail.
How many pixels fit in 300KB?
300KB stretches to about 1810 × 1350 at balanced quality and roughly 2560 × 1920 with heavy compression, so a Full HD frame fits with room to spare. Large flat areas such as sky or a studio backdrop push it further; dense foliage or crowds pull it back.
| Compression level | Bits per pixel | Pixel budget | Square | 4:3 frame |
|---|---|---|---|---|
| Heavy compressionartifacts visible up close | ~0.5 | 4.9 MP | 2210 × 2210 | 2560 × 1920 |
| Balancedclean at normal viewing size | ~1 | 2.5 MP | 1560 × 1560 | 1810 × 1350 |
| High qualityhard to tell from the original | ~2 | 1.2 MP | 1100 × 1100 | 1280 × 960 |
Each row divides the 2,457,600 bits in 300KB by the bits per pixel, then fits that many pixels into a square and a 4:3 frame, rounded down to the nearest 10 pixels. Turn the 4:3 figure on its side for a portrait photo.
These figures are rules of thumb for JPG photos, not guarantees. Smooth skin, sky and plain walls need far fewer bits than foliage, fabric, small text or low-light grain, so the same pixel count can land well under or over the target. WebP, which PNG, WebP and GIF uploads are saved as, usually needs fewer bits than JPG for a similar look.
Making a 300KB image look its best
On a website, resize to the width the layout actually uses. A hero spanning a 1,440-pixel screen does not need to be 4,000 pixels wide; at 1,920 pixels it covers common desktop widths, and 300KB lets it keep balanced quality.
Consider WebP for anything going on your own site. Every current major browser displays it, and it typically looks cleaner than JPG at the same 300KB. A PNG or WebP upload gets you a WebP result directly; for JPG photos, convert with JPG to WebP and compress that file.
Watch gradients. Skies, sunsets and soft studio backgrounds are where low-quality JPG shows banding first. If you see stepped bands in the preview, resize slightly smaller rather than accepting the lower quality.
300KB compared with nearby sizes
| Target | Pixels at ~1 bit per pixel | Approx. 4:3 size | Compared with 300KB |
|---|---|---|---|
| 200KB | 1.6 MP | 1470 × 1100 | 0.67× the pixels, about 18% narrower and shorter |
| 300KB | 2.5 MP | 1810 × 1350 | Current target |
| 500KB | 4.1 MP | 2330 × 1740 | 1.67× the pixels, about 29% wider and taller |
300KB holds 1.5 times the pixels of 200KB and 60% of the pixels of 500KB. For a single web image, gains above 300KB are often hard to see at normal size, while the extra download time on a slow connection is not.
Frequently asked questions
For a large, prominent image such as a hero banner or featured photo, yes: it is enough for a sharp 1920 × 1080 picture. For thumbnails and inline images, 100KB to 150KB is usually plenty, and smaller files load faster on mobile.
Resize it first to around 1,800 to 2,000 pixels on the long side, then compress with a 300KB target. A 5MB camera photo is usually 12 megapixels or more, and reaching 300KB through quality alone would mean discarding about 94% of the file, which leaves visible artifacts.
No. The compressor changes only how the image is encoded, so a 1920 × 1080 image stays 1920 × 1080. To change the dimensions, use an image resizer before compressing.
WebP, if it is for your own website: at the same 300KB it usually holds more detail. Use JPG where WebP is not accepted, such as some upload forms and older software.
Other target sizes
Reviewed by Raja Jahangir · Last reviewed: October 7, 2026