DPI, PPI and Print Size: How Big Can You Print an Image?
What DPI and PPI really mean, the simple formula that tells you how large an image can be printed, how many pixels you need for flyers, posters and banners, and why vectors avoid the problem completely.
"Please send the image at 300 DPI." Printers say it all the time, and it confuses almost everyone, because changing the DPI number in a program often seems to do nothing at all. The idea behind it is actually simple. Once you understand it, you can tell in seconds whether a picture will print sharply at the size you need.
PPI and DPI: two different things
- PPI (pixels per inch) describes an image: how many of its pixels will be placed along each inch of paper.
- DPI (dots per inch) describes a printer: how many tiny ink dots it can place per inch.
People often say DPI when they mean PPI, and printers usually do. When a print shop asks for "300 DPI", it means: *there should be at least 300 pixels of image for every inch of the printed size*.
The only formula you need
Print size (in inches) = pixels ÷ PPI.
Some examples at 300 PPI:
- 3000 × 2000 pixels → 10 × 6.7 inches (about 25 × 17 cm)
- 1800 × 1200 pixels → 6 × 4 inches, a standard photo print
- 1200 × 1200 pixels → 4 × 4 inches
- 600 × 600 pixels → 2 × 2 inches
For centimetres, divide the inches by 2.54 or work directly: pixels needed = centimetres ÷ 2.54 × PPI.
Why changing the DPI number does nothing
An image file stores pixels. The DPI value inside it is only a label that suggests how large to print it. If you change a 1200-pixel-wide image from 72 to 300 DPI without resampling, it still has 1200 pixels; the program simply says it will print at 4 inches instead of 16.7 inches. No detail is added.
To actually get more pixels, you have to resample (upscale) the image, and that invents pixels between the existing ones. Simple upscaling makes the image bigger but blurrier. AI upscalers do better on many images, but they still guess.
How many pixels per inch do you really need?
300 PPI is a safe rule for things viewed up close, but larger prints are seen from further away and need less:
- Business cards, flyers, brochures, photo prints: 300 PPI.
- Posters viewed at arm's length: 150–200 PPI.
- Large posters and roll-up banners: 100–150 PPI.
- Billboards and building wraps, seen from far away: as little as 20–50 PPI.
So a 3000-pixel-wide image is plenty for a 10-inch flyer, fine for a 20-inch poster at 150 PPI, and acceptable for a larger banner seen from a distance.
Checking an image before you print
- Find the image's pixel size. On Windows, right-click the file → Properties → Details. On a Mac, open it in Preview and choose Tools → Show Inspector.
- Divide the width in pixels by the width you want to print, in inches. The result is your PPI.
- Compare it with the list above. If it is far too low, find a larger original or consider converting the image to vector.
Where vectors change everything
Everything above applies to raster images, made of pixels. Vector images — SVG, PDF, EPS, AI — have no pixels and no PPI. They are described as shapes and are drawn at the printer's full resolution at any size. A vector logo prints just as sharply on a business card as on a 3-metre banner, from the same small file.
That is why print shops ask for logos, text and illustrations as vector files. If all you have is a low-resolution JPG or PNG of a logo or graphic, converting it to vector can solve the resolution problem for good. An image vectorizer such as Vectorizo traces the shapes and colors into an SVG that can be printed at any size. Read how to fix a blurry logo for the full process.
Tip: vectorizing works best for artwork made of shapes and flat colors. A photograph should stay a raster image; for a large photo print, start from the original camera file instead.
Screen versus print
On screens, image size is measured in pixels only; the DPI value in a file has no effect on how a website displays it. A common myth says web images must be "72 DPI". What matters for the web is the pixel dimension and the file size, not the DPI label.
Summary
PPI is pixels per printed inch, and print size equals pixels divided by PPI. Aim for 300 PPI for close-up prints and less for big prints seen from afar. Changing the DPI number alone adds no detail. For logos and graphics, a vector file avoids the question completely, because it stays sharp at any size.