These three terms are used interchangeably, which causes a lot of confusion. They are related but not the same.
Resolution
Resolution is simply the number of pixels in an image, such as 4000 x 3000. More pixels mean more detail and a bigger file. It is a fixed property of the picture.
PPI (pixels per inch)
PPI describes how densely pixels are packed on a screen or when an image is displayed at a given size. A phone display is around 400 PPI. It is a ratio, not a property of the file.
DPI (dots per inch)
DPI describes how many dots of ink a printer places per inch. Print quality depends on how many image pixels you map into each inch of paper. Professional photo prints usually need about 300 DPI, large posters viewed from a distance can be 100 to 150 DPI, and screens only show 72 to 110 pixels per inch effectively on the web.
How many pixels do I need?
Multiply the print size in inches by the DPI you want:
| Print size | At 300 DPI | At 150 DPI |
|---|---|---|
| 4 x 6 in | 1200 x 1800 | 600 x 900 |
| 5 x 7 in | 1500 x 2100 | 750 x 1050 |
| 8 x 10 in | 2400 x 3000 | 1200 x 1500 |
| A4 (8.3 x 11.7 in) | 2480 x 3508 | 1240 x 1754 |
| 18 x 24 in poster | 5400 x 7200 | 2700 x 3600 |
Check what you have
Drop your image into the Image Size Finder. It shows the pixel size and the print size in centimetres at 300, 150 and 72 DPI, so you immediately know how large you can print.
The “72 DPI for web” myth
You will often read that web images must be 72 DPI. The DPI number stored in a file does not affect how it looks on screen. Only the pixel dimensions matter. A 1200 pixel wide image looks identical whether its metadata says 72 or 300.
My image is too small for the print size
You have a few options:
- Print smaller. The easiest and best fix.
- Accept a lower DPI for pictures that will be viewed from a distance.
- Enlarge with the Image Upscaler. It smooths and sharpens but cannot add real detail.
- Re-shoot or find a higher-resolution original.
Print a big image on ordinary printers
Use Print Image on Multiple Pages to split a picture across several A4 or Letter pages and assemble a poster.
Key takeaways
- Resolution = total pixels
- PPI = pixel density on screens
- DPI = printer dots per inch
- For prints, aim for about 300 DPI for close viewing and 150 DPI for large posters
The one rule to remember
Pixels are the real size of a digital image. DPI and PPI only describe how those pixels are spread across a physical size. A 3000 x 2000 pixel photo is the same file whether it is labelled 72 or 300 DPI. Changing the label does not change quality, only the default print size.
How big can you print?
Divide the pixel dimensions by the DPI you need. At 300 DPI, which is standard for sharp prints:
| Print size | Pixels needed at 300 DPI |
|---|---|
| 4 x 6 in | 1200 x 1800 |
| 8 x 10 in | 2400 x 3000 |
| A4 | 2480 x 3508 |
| A3 | 3508 x 4961 |
For posters viewed from a distance, 150 DPI is often enough, and 100 DPI can be acceptable for large banners.
What if you do not have enough pixels?
First check your image with image size finder. If it is too small, enlarge it with the image upscaler, but be realistic: upscaling improves edges, it cannot create detail.
Screens versus print
Websites ignore DPI completely. What matters is width and height in pixels, so resize with the image resizer. If you are planning a print layout, the aspect ratio calculator helps you pick a size that fits the paper.
Frequently asked questions
How many pixels do I need to print an A4 page?
About 2480 x 3508 pixels for a sharp 300 DPI print, or 1240 x 1754 pixels for an acceptable 150 DPI print.
Does 72 DPI matter for web images?
No. On screens only the pixel dimensions matter. The DPI value stored in a file does not change how it displays.
What DPI should I use for printing photos?
300 DPI for prints viewed up close. Posters seen from a distance can use 100 to 150 DPI.
Can I increase DPI without losing quality?
Changing the DPI number alone does not add detail. Real quality needs more pixels, which means a higher-resolution original.
