ImageToolkit
← Guides
Image resolution vs file size — what's the difference?
Understand once and for all the difference between resolution (pixels), DPI and file size in KB/MB. Complete practical guide.
What is image resolution?
Image resolution is the number of pixels an image has, expressed as width × height in pixels, for example: 1920 × 1080 px. The more pixels, the more detail the image has and the larger the file size.
What is DPI and what is it for?
DPI (Dots Per Inch) is a measurement used mainly for printing. It indicates how many ink dots are printed per inch on paper.
- 72 DPI: standard for screens — irrelevant for web
- 150 DPI: basic printing
- 300 DPI: professional quality printing
💡 Important: For web and social media images, DPI doesn't matter — what matters is the number of pixels. A 72 DPI image with 1080px width has the same visual quality on screen as a 300 DPI image with 1080px.
Relationship between resolution and file size
| Resolution | PNG uncompressed | JPG (80%) | WebP (80%) |
|---|---|---|---|
| 400 × 300 px | ~350 KB | ~25 KB | ~18 KB |
| 1920 × 1080 px | ~6 MB | ~500 KB | ~350 KB |
| 4000 × 3000 px | ~34 MB | ~2.5 MB | ~1.5 MB |
How to reduce file size without losing resolution?
Use compression! Compressing an image at 80% quality drastically reduces the file size without changing the resolution. Use our compress image tool for this.