What this calculator does
The Image Print Resolution (DPI) Calculator converts the pixel dimensions of a digital image into the physical size it can be printed at a given resolution. DPI (dots per inch) describes how many pixels are packed into each printed inch — the higher the DPI, the sharper the print but the smaller the maximum size for a fixed pixel count.
How to use it
Enter your image's width and height in pixels (you can find these in any photo viewer or image editor), then enter the print resolution you want. A common standard for high-quality photo prints is 300 DPI, while 150–200 DPI is acceptable for posters viewed from a distance. The calculator returns the print size in inches and centimeters, plus the image's megapixel count.
The formula explained
The core relationship is simple division: inches = pixels ÷ DPI. Because there are 2.54 centimeters in an inch, the centimeter size is just the inch size multiplied by 2.54. Megapixels are computed as (width × height) ÷ 1,000,000.
$$\text{Print Size (in)} = \frac{\text{Width (px)}}{\text{DPI}} \times \frac{\text{Height (px)}}{\text{DPI}}$$$$\text{Print Size (cm)} = \left(\frac{\text{Width (px)}}{\text{DPI}} \times 2.54\right) \times \left(\frac{\text{Height (px)}}{\text{DPI}} \times 2.54\right)$$$$\text{Megapixels} = \frac{\text{Width (px)} \times \text{Height (px)}}{1{,}000{,}000}$$
Worked example
A 3000 × 2400 pixel photo printed at 300 DPI gives \(3000 \div 300 = 10\) inches wide and \(2400 \div 300 = 8\) inches tall — a standard 8×10 print. In centimeters that is \(25.4 \times 20.32\) cm. The image is \(3000 \times 2400 = 7{,}200{,}000\) pixels, or 7.2 megapixels.
FAQ
What DPI should I use for printing? 300 DPI is the gold standard for photographs and detailed prints. For large posters or banners viewed from a few feet away, 150 DPI is usually fine.
Is DPI the same as PPI? In casual use they are used interchangeably for digital images. Strictly, PPI (pixels per inch) describes the image file and DPI describes printer dots, but for this calculator they mean the same thing.
Can I print bigger than the calculated size? Yes, but the effective DPI drops and the print may look soft or pixelated. Lowering the DPI value here shows you the larger size you can achieve at reduced sharpness.
