Pick one of three modes below. Nothing is uploaded and no account is needed: your numbers stay on this page.

Three calculations

  • Pixels to print size at a PPI. Enter the pixel width and height of your photo and a PPI. The calculator returns the theoretical physical size at the PPI you enter.
  • Print size to required pixels. Enter the print size you need and a PPI. The calculator returns the pixel dimensions required, rounded up to whole pixels.
  • Effective PPI for Fit or Fill. Enter the photo's pixels and a Frame size. The calculator returns the PPI for each fit mode, so you can see how much of the photo is visible.

Formulas

The conversions use these formulas:

  • inches = pixels ÷ PPI
  • millimetres = inches × 25.4
  • centimetres = inches × 2.54
  • required pixels = inches × PPI, rounded up

Worked example: 1200 × 1800 px

At 300 PPI, 1200 × 1800 px gives an intended physical size of 4 × 6 in, which is 101.6 × 152.4 mm. That is an exact conversion of the inch size. It is not exactly 10 × 15 cm, because 10 × 15 cm is a different metric size. To print 4 × 6 in at 300 PPI, you need 1200 × 1800 px.

Example: Fit and Fill in a 6 × 6 in Frame

Take a 1200 × 1800 px photo and place it in a 6 × 6 in Frame. The two fit modes give different results:

  • Fit at 300 PPI. The whole photo fits inside the Frame. The visible Content is 4 × 6 in, so about one third of the Frame area is unused.
  • Fill at 200 PPI. The Content is scaled to 6 × 9 in and cropped to the Frame. About one third of the Content area is cropped away.

For a Frame of frameWidthIn × frameHeightIn and a photo of widthPx × heightPx, both edge ratios matter: Fit PPI = max(widthPx ÷ frameWidthIn, heightPx ÷ frameHeightIn), and Fill PPI = min(widthPx ÷ frameWidthIn, heightPx ÷ frameHeightIn). In the square 6 × 6 in example, the 1200 px edge gives 200 PPI and the 1800 px edge gives 300 PPI. Fit therefore uses 300 PPI, and Fill uses 200 PPI.

What PPI means here

PPI in this calculator means the pixel density of your source image, meaning pixels per inch of print. It is not your printer's DPI. Changing the DPI value stored in a file's metadata does not create new detail, so it does not change the pixels available for printing.

What the calculator does not do

The calculator gives arithmetic, not a quality or print-size guarantee. It does not model borders, bleed, extra Content zoom, or rotation. It does not pack paper, check printer margins, modify your photo, detect paper stock, or set printer scaling. Use the source pixels of the file you will print, after any editing and cropping.

Use the numbers in PrintExactly for Mac

Use this calculator for a quick check, then set the sizes in PrintExactly for Mac. The app works with a Page (the paper) and Frames (the physical print positions) that hold the Content.

  1. Enter the photo's pixels and the size you need here, and note the PPI.
  2. Create a Frame in the app at that size, and set the Content fit.
  3. Check the printable area the printer reports for the paper you have loaded, and keep any bleed or crop marks inside it.
  4. Print at 100% with scale-to-fit turned off in the driver, then measure a test print with a ruler before the full job.

PrintExactly for Mac limits each Frame side to 2,000 mm. The calculator can calculate sizes above that limit, but a calculated size above 2,000 mm on either side cannot be set as one Frame in the app, and the calculator does not check whether a printer or paper can handle it.

Frequently asked questions

What is the difference between PPI here and printer DPI?

PPI here is the pixel density you choose: source pixels divided by the print size in inches. It is not the printer's DPI, which describes the printer's dot placement. Changing a file's DPI metadata does not add or remove pixels, so it does not change the print size this calculator reports.

Why does 1200 × 1800 px at 300 PPI not give exactly 10 × 15 cm?

The result is 4 × 6 in, which is 101.6 × 152.4 mm. A 4 × 6 in print is a common photo size, but 10 × 15 cm is a metric label for a slightly different size. Enter the size you actually need, then check the result against the Frame you create in the app.

Does a Fit or Fill result guarantee good print quality?

No. The calculator does arithmetic on the numbers you enter. It does not judge sharpness, colour, or how a printer will render the photo. Use the effective PPI as a guide. Then print a test at 100%, check its sharpness yourself, and measure its physical size with a ruler.

Should I calculate with the original file or an edited crop?

Use the pixel dimensions of the image you will actually print, after any editing or cropping. Borders, bleed, extra Content zoom, and rotation are not part of this calculation, so they must be accounted for separately.