How to use it
- Choose What to calculate: a print size from pixels, the pixels for a print, the largest print at 300, 240 and 150 dpi, or the dpi of a print.
- For a picture, type its Width (pixels) and Height (pixels). For a print, type the Print width and Print height and choose the Unit.
- Type the Dots per inch (dpi) where it is asked for. 300 is the usual choice for prints seen up close.
- Read the Print size, the Pixels needed or the Resolution of the print, or the table Largest print at each dpi.
Pixels, dots per inch and inches
A print size follows from two numbers: the pixel count and the dots per inch. Divide the pixels by the dpi to get the length in inches: 3000 pixels at 300 dpi is 10 inches. The Wikipedia article on pixel density gives the same relation: the number of pixels equals the size in inches times the pixels per inch.
One inch is exactly 2.54 cm (Wikipedia: Inch), so the conversion between the two units has no rounding in it. The calculator rounds only the results it shows.
print length (in) = pixels ÷ dpi
pixels needed = length (in) × dpi
centimetres = inches × 2.54Which dpi for which print
The Wikipedia article on pixel density reports that the unaided eye generally cannot tell detail apart beyond about 300 pixels per inch, and that this figure depends on the distance between viewer and image. A print held close is therefore worth 300 dpi. A large print seen from further away, such as a poster, can use 240 or 150 dpi and still look sharp at its viewing distance. The table shows the size each choice gives for the same pixels.
A printer's dpi and a picture's pixels per inch are different measures. The Wikipedia article on dots per inch says inkjet printers are typically capable of 300 to 720 dpi, and that the printer's dpi is usually well above the pixels per inch of the picture, because each pixel is printed with several dots. The article on pixel density suggests a printer at 600 dpi for an image of 300 ppi, that is half the printer's dpi or less.
What the calculator does not cover
The calculator works from the pixels of the picture as they are. If a picture is cropped or resized before printing, use its new pixel count. Paper size, margins, colour profile and the printer's own settings are not part of the calculation.
Example: a 24-megapixel camera photo
A photo of 6000 by 4000 pixels is printed at the largest size each dpi allows. At 300 dpi the print is 20.0 by 13.3 inches, which is 50.8 by 33.9 cm. Lowering the dpi enlarges the print: 240 dpi gives 25.0 by 16.7 inches, and 150 dpi gives 40.0 by 26.7 inches.
| dpi | Centimetres | Inches |
|---|---|---|
| 300 | 50.8 × 33.9 | 20.0 × 13.3 |
| 240 | 63.5 × 42.3 | 25.0 × 16.7 |
| 150 | 101.6 × 67.7 | 40.0 × 26.7 |
Frequently asked questions
Which dpi should I use for a photo print?
300 dpi is the usual choice for a print viewed up close. The Wikipedia article on pixel density says the unaided eye generally cannot separate detail beyond about 300 pixels per inch, although that depends on the viewing distance. For a large print seen from further away, 240 or 150 dpi makes a bigger print from the same pixels.
Why does a 600 dpi printer not need 600 pixels per inch?
The Wikipedia article on pixel density says that for inkjet printers it is generally good practice to use half the printer's dpi or less as the image's ppi. A 600 dpi printer therefore suits an image of 300 ppi, because each pixel is reproduced with several printer dots.
Is 240 dpi a standard print resolution?
It is not a fixed standard. The Wikipedia article on dots per inch lists 300 to 360 dpi, and 240 dpi, among the resolutions of early printers, and 300 to 720 dpi for inkjets. The table shows what 240 dpi gives for the same picture.
How many pixels does a 10 by 15 cm print need?
At 300 dpi, 10 cm is 3.94 inches, which needs 1,181 pixels, and 15 cm is 5.91 inches, which needs 1,772 pixels. Use the pixels-needed mode with these numbers to check.
Why do the dpi figures differ across and down?
The dpi follows from the pixel count and the print size on each side. If a print has a different shape from the picture, the picture is cropped or stretched, and the across and down dpi differ. The calculator then shows both.
Is my picture uploaded when I calculate?
No. Only the numbers you type are used, and they are worked out in your browser. The picture itself is never sent anywhere.
Sources
Figures and text last checked on Tuesday, November 10, 2026.