DPI vs PPI, and what resolution you need for printing
DPI and PPI get used as if they were the same thing, and for most purposes they are. What matters is how many pixels you have and how big you want to print.
Short answer: PPI (pixels per inch) describes an image; DPI (dots per inch) describes a printer. In everyday use they mean the same thing: how many image pixels go into each inch of paper. For sharp prints viewed up close, aim for 300 PPI; 150–200 is usually fine for posters seen from further away.
DPI vs PPI: what each term means
PPI, pixels per inch, is a property of a digital image when you print it, or of a screen. An image that is 3000 pixels wide printed 10 inches wide is at 300 PPI.
DPI, dots per inch, strictly describes how finely a printer lays down ink. An inkjet may place 1200 or more tiny dots per inch and combine several of them, in different colours, to reproduce a single image pixel. So a printer's DPI is normally far higher than the image's PPI, and the two numbers are not directly comparable.
In practice almost everyone, including photo labs, print shops and software such as Photoshop and Word, says "DPI" when they mean the image's PPI. If a print shop asks for a "300 DPI file", they mean an image with enough pixels to give 300 pixels per inch at the final print size. This guide, and the DPI calculator, use the terms that way.
The one formula you need
Everything comes from a single relationship:
- pixels = inches × DPI
- inches = pixels ÷ DPI
- DPI = pixels ÷ inches
For centimetres, divide by 2.54 first (or multiply the result by 2.54). Example: a 10 × 15 cm print is 3.94 × 5.91 in, so at 300 DPI it needs 1181 × 1772 pixels.
How many pixels you need for common print sizes
Megapixels (MP) are width × height ÷ 1,000,000. Use the 300 DPI column for photos and documents, and the lower columns when the print will be viewed from further away.
| Print size | 300 DPI | 200 DPI | 150 DPI |
|---|---|---|---|
| 4 × 6 in | 1200 × 1800 (2.2 MP) | 800 × 1200 (1.0 MP) | 600 × 900 (0.5 MP) |
| 5 × 7 in | 1500 × 2100 (3.1 MP) | 1000 × 1400 (1.4 MP) | 750 × 1050 (0.8 MP) |
| 8 × 10 in | 2400 × 3000 (7.2 MP) | 1600 × 2000 (3.2 MP) | 1200 × 1500 (1.8 MP) |
| 8.5 × 11 in (Letter) | 2550 × 3300 (8.4 MP) | 1700 × 2200 (3.7 MP) | 1275 × 1650 (2.1 MP) |
| 11 × 14 in | 3300 × 4200 (13.9 MP) | 2200 × 2800 (6.2 MP) | 1650 × 2100 (3.5 MP) |
| 12 × 18 in | 3600 × 5400 (19.4 MP) | 2400 × 3600 (8.6 MP) | 1800 × 2700 (4.9 MP) |
| 16 × 20 in | 4800 × 6000 (28.8 MP) | 3200 × 4000 (12.8 MP) | 2400 × 3000 (7.2 MP) |
| 18 × 24 in | 5400 × 7200 (38.9 MP) | 3600 × 4800 (17.3 MP) | 2700 × 3600 (9.7 MP) |
| 24 × 36 in | 7200 × 10800 (77.8 MP) | 4800 × 7200 (34.6 MP) | 3600 × 5400 (19.4 MP) |
| A5 | 1748 × 2480 (4.3 MP) | 1165 × 1654 (1.9 MP) | 874 × 1240 (1.1 MP) |
| A4 | 2480 × 3508 (8.7 MP) | 1654 × 2339 (3.9 MP) | 1240 × 1754 (2.2 MP) |
| A3 | 3508 × 4961 (17.4 MP) | 2339 × 3307 (7.7 MP) | 1754 × 2480 (4.3 MP) |
| A2 | 4961 × 7016 (34.8 MP) | 3307 × 4677 (15.5 MP) | 2480 × 3508 (8.7 MP) |
For the full list of paper sizes in pixels, see the A paper sizes chart.
How big can I print the image I already have?
Go the other way: divide the pixel dimensions by the DPI you want.
| Image | Pixels | At 300 DPI | At 150 DPI |
|---|---|---|---|
| 12 MP phone photo | 4032 × 3024 | 13.4 × 10.1 in | 26.9 × 20.2 in |
| 24 MP camera | 6000 × 4000 | 20.0 × 13.3 in | 40.0 × 26.7 in |
| Full HD video frame | 1920 × 1080 | 6.4 × 3.6 in | 12.8 × 7.2 in |
| 4K video frame | 3840 × 2160 | 12.8 × 7.2 in | 25.6 × 14.4 in |
| Instagram portrait post | 1080 × 1350 | 3.6 × 4.5 in | 7.2 × 9.0 in |
A typical 12-megapixel phone photo gives a sharp print of about 13 × 10 inches at 300 DPI, and a perfectly usable 20 × 27 inch poster at 150 DPI. Social media images are much smaller: a 1080 px wide post is only good for about 3.6 inches at 300 DPI, so download the original rather than a copy saved from an app.
What DPI do you actually need?
The right number depends on how close people stand to the print. These are widely used rules of thumb, not hard limits:
| Use | Typical target |
|---|---|
| Photos, flyers, books, documents (held in the hand) | 300 DPI |
| Large photo prints on a wall, A3 and up | 200–300 DPI |
| Posters viewed from a metre or two | 150–200 DPI |
| Roll-up banners and exhibition graphics | 100–150 DPI at full size |
| Billboards viewed from the street | Often 30–50 DPI or lower |
| Screens, websites, slides | DPI is irrelevant; only pixel dimensions matter |
If your image falls short, printing a little smaller is the cleanest fix. Upscaling software can help a bit with low-detail images, but it cannot invent real detail.
Why the "DPI" field in an image file is misleading
JPG, PNG and TIFF files can store a DPI number in their metadata, often 72 or 96 by default. That number does not change the image at all. A 3000 × 2000 px photo tagged as 72 DPI and the same photo tagged as 300 DPI contain exactly the same pixels; the tag only tells layout software what size to place it at by default.
- Changing the DPI without resampling (in Photoshop, untick "Resample") changes the print size, not the quality.
- Changing the DPI with resampling adds or removes pixels. Adding pixels this way makes the file bigger but not sharper.
- The "72 DPI for web" rule is a leftover from early Mac screens. Browsers ignore the tag and display images by pixel size.
So when someone asks for "a 300 DPI image", the useful question is: at what print size? Then work out the pixels with the table above or the calculator.
Screens: PPI without printing
Screens have a fixed PPI set by their hardware. A 27-inch 4K monitor is about 163 PPI; a 27-inch 1440p monitor about 109 PPI; phones are typically 400–500 PPI. The image on screen is sized by its pixels and the device's scaling, never by the DPI tag in the file. That is why a "300 DPI" logo can look tiny on a website: it may simply not have many pixels.
Frequently asked questions
Is 72 DPI good enough for printing?
Only if the image has enough pixels for the size you want. The DPI tag itself does not matter. A 2400 × 3000 px image prints a sharp 8 × 10 inch photo whether it is tagged 72 or 300 DPI, as long as you print it at 8 × 10.
How many megapixels do I need for an A4 print?
About 8.7 MP (2480 × 3508 px) for 300 DPI. Around 3.9 MP (1654 × 2339 px) gives 200 DPI, which still looks good for most photos.
Can I print a 1080 × 1080 Instagram photo?
At 300 DPI it makes a 3.6 inch (9.1 cm) square. At 200 DPI you can stretch it to about 5.4 inches. For anything bigger, find the original photo on your phone.
Does a higher printer DPI make my photo sharper?
Up to a point. Printer DPI controls how finely ink is laid down, which affects smoothness of tones. It cannot add detail that is not in the image, so the image PPI is usually the limiting factor.