DPI & Print Size Calculator

Reading the result

Pixels are the only thing a printer actually has to work with. DPI simply decides how tightly those pixels are packed onto the paper: pack them tighter and the print is smaller but crisper; spread them out and the print grows but softens. This calculator does that division for you in both inches and centimetres. To convert a single measurement either way — pixels to inches, or inches to the pixels you need — use the pixels to inches converter. Short of pixels for the print you want? The image upscaler enlarges a photo 2× to 4× with edge sharpening, which is usually enough to take a phone snapshot from 150 to 300 DPI at the same print size.

Common print targets

• 6x4 inch photo at 300 DPI — needs at least 1800 x 1200 pixels.
• A4 flyer at 300 DPI — needs about 2480 x 3508 pixels.
• A2 poster at 150 DPI — needs about 2480 x 3508 pixels.
• Passport photo at 600 DPI — needs about 1200 x 1200 pixels for a 2x2 inch print.

What DPI actually is

DPI stands for dots per inch, and it only means anything once an image is printed. A digital file has a pixel count — 4000 by 3000, say — and that number does not change. DPI is the answer to a different question: over how many inches are you going to spread those pixels? Spread 4000 pixels across 10 inches and you have 400 DPI. Spread the same 4000 across 40 inches and you have 100 DPI and a visibly soft print.

This is why "save it at 300 DPI" is not a thing you can do to a file to improve it. The DPI value stored in an image's metadata is a suggestion to whatever prints it; changing it without changing the pixel count changes the printed size, not the quality.

Pixels you need for common print sizes

300 is a default, not a law

300 DPI became the standard because it is roughly the limit of what a person resolves at normal reading distance, about 30 centimetres. Anything you hold — a photo print, a book page, a business card — deserves it. Things you stand back from do not. A poster viewed from two metres is fine at 150 DPI; a billboard is routinely produced at 20. The working rule is that the required resolution falls off with viewing distance, so ask how far away the print will be before you panic about the number.

When you do not have enough pixels

• Print smaller. The same file at 8 × 10 inches instead of 16 × 20 doubles the effective DPI.
• Crop less. Every crop takes pixels away from the print.
• Go back to the original. Camera originals, RAW files and phone exports are usually larger than the copy that reached you through a chat app.
• Accept a lower DPI for a print that will hang on a wall rather than sit in your hands.
• Do not upscale and call it 300 DPI. Interpolated pixels contain no new detail, and the print will show it.

DPI versus PPI

Strictly, PPI is pixels per inch in a digital image and DPI is ink dots per inch laid down by a printer, which uses several dots to make one pixel's colour. In everyday use the two words are swapped freely and no harm comes of it. The distinction matters only when a printer's spec sheet quotes a very large DPI — a 4800 DPI inkjet is not asking you for a 4800 PPI file.