How to use the image print size and dpi calculator
- Choose what to find: the print size from pixels, the pixels for a print size, or the DPI of an image at a print size.
- Enter the image size in pixels, or the print size in inches, and the DPI if the mode needs it.
- Set the resolution you want to meet. The number in the field is an example, and it is used for the table of common print sizes.
- Read the answer and the table that shows the DPI your image gives at each common print size.
Formula
Print size in inches = pixels / DPI
Pixels needed = inches x DPI, rounded up
DPI = pixels / inches (the lower of width and height is used)
1 inch = 2.54 centimeters
In the table, the long side of the image is matched to the long side of the print.
A 4000 x 3000 pixel photo
At 300 DPI, 4000 x 3000 pixels print at 13.33 x 10.00 inches, which is 33.9 x 25.4 centimeters, and the image has 12 megapixels. A 10 x 8 inch print at 300 DPI needs 3,000 x 2,400 pixels.
Over a 10 x 8 inch print, the same photo has 400 DPI across the width and 375 DPI down the height, so 375 DPI limits the print. In the table, 4 x 6 gives 667 DPI, 8 x 10 gives 375, 11 x 14 gives 273, 16 x 20 gives 188 and 20 x 30 gives 133.
What DPI really is
DPI means dots per inch, a printing term for how many pixels are spread over an inch of paper. An image file has a fixed number of pixels, and the DPI only says how much paper they cover. A higher DPI means a smaller print with finer detail, and a lower DPI means a larger print with coarser detail.
So the DPI stored in a file does not change its quality. What matters is the pixel count compared with the print size. This is why the tool asks for pixels and a size and then works out the rest.
Choosing a resolution target
The resolution you need depends on the printer, the paper and how closely the print is viewed. A poster seen from across a room can use a lower DPI than a photo held in the hand. Ask your printer which resolution it wants, and enter it as your goal. The default is an example.
Cropping uses up pixels, so crop first and then check the size. For resizing, use the image resizer, for shapes the aspect ratio calculator, and for file size the image compressor. The crop image tool handles trimming.
Assumptions and limits
- DPI here means pixels per inch of print.
- The goal resolution is a number you choose, and 300 is only a default example.
- Pixel counts are whole numbers, and needed pixels are rounded up.
- The table assumes no cropping and matches the long side to the long side.
Frequently asked questions
How do I find the print size of an image?
Divide the pixel width and height by the DPI. At 300 DPI, 4000 x 3000 pixels is 13.33 x 10.00 inches.
How many pixels do I need for an 8 x 10 print?
Multiply each side by the DPI. At 300 DPI you need 2,400 x 3,000 pixels.
Does changing the DPI in a file improve quality?
No. It changes only how large the pixels print. Quality depends on the number of pixels compared with the print size.
What DPI should I use?
Ask your printer, because it depends on the printer, paper and viewing distance. Enter that number as the goal and the table shows which sizes meet it.