You exported a 3000 by 2400 px photo and the print shop asks: “Is this 300 DPI?” Annoying question, simple answer. Punch the pixels and the print size in and you get the DPI back instantly. Flip it around and the same calculator tells you how big a 1920 px image can print before it looks soft, or exactly how many pixels you need to fill an 8 by 10 at 300.
What DPI actually means here
DPI stands for dots per inch. PPI is pixels per inch. On a screen the correct word is PPI, on a printer it’s DPI, but for this kind of resolution math they’re the same number and the calculator treats them as one. The relationship never changes:
- DPI = pixels ÷ inches
- pixels = inches × DPI
- inches = pixels ÷ DPI
That’s the whole engine. Three variables, lock any two, the third pops out. The tool does it per axis, so a non-square image gives you a width DPI and a height DPI separately. If those two numbers don’t match, your pixel ratio doesn’t match the print ratio and the image will stretch. Good thing to catch before you pay for a print.
Picking a DPI
Different jobs want different numbers, and guessing wrong wastes either file size or sharpness.
- 72 is the old “screen resolution” from early Mac days. Mostly historical now, but it still shows up in legacy specs.
- 96 is what CSS and Windows assume for a logical inch. Handy when you’re sizing things for the web.
- 300 is the print standard. Photo books, magazines, business cards, posters viewed up close all target this.
- 150 is fine for drafts or big banners you’ll stand back from.
- 600 is fine-art and line-art territory.
The built-in presets cover all of these with one click. Set the DPI, type your print size, and the pixels-needed value updates as you type.
A quick gut check for print size
The reference table at the bottom takes a single pixel length and shows what it becomes at 72, 96, 150, 300, and 600 DPI, in both inches and centimeters. Drop in 1920 and a Full HD width is a generous 26 inches at 72 DPI but only 6.4 inches at 300. Same pixels. The DPI decides how big they spread out.
Rule of thumb worth memorizing: more DPI in the same pixels means a smaller, sharper print. Stretch those pixels across a bigger area and DPI drops, and below roughly 200 DPI photo prints start looking mushy up close. It’s all arithmetic too, so nothing uploads and the result updates the instant you change a field.
FAQ
Is DPI the same as PPI? For resolution math, yep. PPI describes pixels on a display, DPI describes ink dots on paper, but the pixels-per-inch calculation is identical. Print folks say DPI, screen folks say PPI.
My photo’s metadata says 72 DPI. Is it ruined? Nope. The DPI tag stored in a file is just a printing hint. It changes nothing about the actual pixels. A 6000 px wide image is 6000 px wide whether the tag reads 72 or 300, and you can print it large at full quality regardless.
How many pixels do I need for a 4 by 6 photo print? At 300 DPI, 1200 by 1800 px. Switch the solver to “Pixel size,” set 300 DPI, type 4 by 6 inches, done.
Why are my width and height DPI different? Because your pixel aspect ratio doesn’t match the print size you asked for. A 3000 by 2000 image forced into an 8 by 10 inch frame can’t keep both axes equal, so something gets cropped or squished. Match the ratios and the two DPI numbers line up.
Does centimeters work too? Yes. Flip the unit toggle to cm and every input and result switches over. Internally it converts through inches at 2.54 cm per inch, so the answers stay exact.