Photo Print Size Calculator
Before sending a photo to print, it helps to know how large you can go while keeping it sharp. Print size in inches is simply your pixel dimensions divided by the target dots per inch. This calculator takes your image width and height in pixels and your chosen DPI, then returns the largest print width and height in inches, the total megapixels, and the aspect ratio. The relationship is an exact definition, so the result depends only on the numbers you enter and the print quality you want.
Print size formula
Print width (inches) = pixel width / DPI
Print height (inches) = pixel height / DPI
Megapixels = (pixel width * pixel height) / 1,000,000
Aspect ratio = pixel width / pixel height
Each printed inch holds DPI pixels by definition, so dividing pixel dimensions by DPI gives the print size. Lowering the DPI prints larger but reduces fine detail.
Print quality context
- About 300 DPI is the common target for sharp photographic prints.
- Large prints viewed from a distance can look good at 150 DPI or less.
- One inch equals exactly 25.4 millimeters under the international definition.
- Upscaling adds interpolated pixels, not real detail, and softens prints.
- Aspect ratio tells you whether the image will crop to a standard frame.
Photo print size: frequently asked questions
What is DPI and why does it matter for prints?
DPI (dots per inch) describes how many image pixels are printed per inch of paper. Higher DPI means finer detail. A common target for sharp photographic prints is 300 DPI, while large prints viewed from a distance can look fine at 150 DPI. The calculator uses the DPI you choose.
How is the maximum print size calculated?
Divide each pixel dimension by the target DPI. A 6,000 by 4,000 pixel image at 300 DPI prints at 20 by 13.33 inches. Lowering the DPI lets you print larger, at the cost of resolution. The formula is exact: print inches equals pixels divided by DPI.
What is the difference between DPI and PPI?
PPI (pixels per inch) describes the digital image, while DPI (dots per inch) describes the printer output. For photo printing they are used interchangeably to mean image pixels per printed inch. This calculator treats your target as image pixels per printed inch.
How many megapixels do I need for a given print?
Multiply the desired print width and height in inches by your DPI to get the pixels needed on each side, then multiply those together and divide by one million for megapixels. The calculator reports the megapixels your image actually has so you can compare.
Can I enlarge a photo beyond its native size?
You can, but upscaling adds pixels by interpolation rather than real detail, so sharpness drops. For the best print, keep your output size within the maximum this calculator reports at your chosen DPI, or accept a lower effective resolution for larger prints.
Official sources
- U.S. National Institute of Standards and Technology: Inch and length definitions.
- International Organization for Standardization: ISO 12233 image resolution standard.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.