DPI vs PPI Explained: What Matters for Print and Screens

PPI (pixels per inch) tells you how many image pixels fit into each inch of a print or a screen. DPI (dots per inch) tells you how many tiny ink or toner dots a printer puts down per inch. When you prepare a photo, the number that decides print quality is PPI, and it comes straight from your pixel dimensions: print size in inches = pixels ÷ PPI.

People mix up the two terms all the time. Many apps and print shops say "DPI" when they mean PPI, so "send it at 300 DPI" almost always means "give me enough pixels for 300 pixels per inch at the size you ordered."

This guide explains each term, shows why changing the DPI number in a file's settings does nothing on screen, walks through print-size math at 300 and 150 PPI, and gives a table of the pixel dimensions you need for common print sizes.

What PPI means for images and displays

A digital image is a grid of pixels, for example 4000 × 3000. That grid has no physical size until you decide how big to show or print it. PPI is what links the pixel count to inches.

PPI of an image

When you print a 4000-pixel-wide image at 10 inches wide, each inch holds 400 pixels, so the print is 400 PPI. Print the same file 20 inches wide and you get 200 PPI. The pixels stay the same. Only how tightly they're packed changes.

That's why an image doesn't really "have" a resolution of 300 PPI. It has a pixel count, and the PPI depends on how large you print it.

PPI of a screen

A display also has a fixed grid of physical pixels, and its PPI comes from its resolution and size. The calculation uses the diagonal:

• A 24-inch 1920 × 1080 monitor: √(1920² + 1080²) = √(3,686,400 + 1,166,400) = √4,852,800 ≈ 2,203 pixels diagonally. 2,203 ÷ 24 ≈ 92 PPI.
• A 27-inch 2560 × 1440 monitor: √(2560² + 1440²) = √(6,553,600 + 2,073,600) = √8,627,200 ≈ 2,937 pixels. 2,937 ÷ 27 ≈ 109 PPI.

Phones and high-density laptop screens pack in far more pixels per inch. Operating systems and browsers deal with this by scaling: one "logical" pixel is drawn with several physical pixels. On the web, the ratio is exposed as devicePixelRatio.

What DPI means for printers

DPI describes the printer, not the image. An inkjet or laser printer can't paint one pixel in an exact color. It builds up each color from many tiny dots of a few inks (usually cyan, magenta, yellow and black) using patterns called halftoning or dithering.

So one image pixel may be made of many printer dots. That's why printer spec sheets often list DPI figures far higher than the roughly 300 PPI that photo files are usually prepared at. The two numbers measure different things and aren't meant to match.

Scanners use DPI as well, but for a scanner it means samples per inch: how many pixels the scanner captures from each inch of the original. Scanning a 4 × 6 inch photo at 600 DPI gives 2400 × 3600 pixels.

Why changing the DPI setting doesn't change your image on screen

Image files such as JPG and PNG can store a resolution value, often 72, 96 or 300. This is metadata, a label attached to the file. It mainly suggests a default print size to software that cares about print.

Screens generally ignore it. A 1200 × 800 image shows 1200 × 800 pixels (before any OS or browser scaling) whether the tag says 72 or 300. Change the tag from 72 to 300 without changing the pixels, and the image looks the same on screen and the file size barely moves. The main difference is that a layout program might now place it at a smaller default size: 1200 ÷ 300 = 4 inches wide instead of 1200 ÷ 72 ≈ 16.7 inches.

This is why "save images at 72 DPI for the web" is a myth. On the web, what matters is pixel dimensions and compression. For more on that, see how to compress images for web without visible quality loss.

Changing the PPI tag vs resampling

Most image editors offer two different operations that are easy to confuse:

• Changing resolution without resampling keeps every pixel and only changes the PPI tag and the implied print size. Quality is unaffected.
• Resampling changes the actual pixel count. Downsampling throws pixels away; upsampling invents new ones. This is the step that can soften an image.

If a print shop asks for "300 DPI," check the pixel dimensions first. Often you only need to change the tag, or nothing at all.

How to calculate print size from pixel dimensions

The formula works both ways:

• Print size (inches) = pixels ÷ PPI
• Pixels needed = inches × PPI
• Effective PPI = pixels ÷ inches

Worked example: a 12-megapixel photo

Say your phone or camera makes a 4000 × 3000 pixel image (4000 × 3000 = 12,000,000 pixels, or 12 MP).

1. At 300 PPI: 4000 ÷ 300 = 13.33 inches, and 3000 ÷ 300 = 10 inches. Maximum print: about 13.3 × 10 inches.
2. At 150 PPI: 4000 ÷ 150 = 26.67 inches, and 3000 ÷ 150 = 20 inches. Maximum print: about 26.7 × 20 inches.
3. At a size you choose, such as 16 × 12 inches: 4000 ÷ 16 = 250 PPI, and 3000 ÷ 12 = 250 PPI. That's a little under 300 but fine for most viewers.

Worked example: a 1920 × 1080 screenshot or video frame

1. At 300 PPI: 1920 ÷ 300 = 6.4 inches, and 1080 ÷ 300 = 3.6 inches, giving 6.4 × 3.6 inches.
2. At 150 PPI: 1920 ÷ 150 = 12.8 inches, and 1080 ÷ 150 = 7.2 inches, giving 12.8 × 7.2 inches.

A full-HD frame makes a sharp small print but a soft large one.

When the aspect ratio doesn't match

A 4000 × 3000 photo has a 4:3 shape (1.33 to 1), while an 8 × 10 print is 5:4 (1.25 to 1). To fill an 8 × 10 in portrait orientation, you have to crop. With the photo turned to 3000 wide by 4000 tall, keep the full 3000-pixel width and trim the height to 3000 × 1.25 = 3750 pixels. The 3000 × 3750 crop prints at 3000 ÷ 8 = 375 PPI (and 3750 ÷ 10 = 375 PPI the other way), which is plenty.

The free image resizer can resize by pixels or percent and crop to preset sizes. If none of the presets matches your print's shape, crop to the right ratio in a photo editor first. Resizing straight to 3000 × 3750 without cropping would stretch the photo.

Pixel dimensions needed for common print sizes

Here's the pixel count for each size at 300 PPI (the usual target for photos) and 150 PPI (a common minimum for acceptable prints). A4 is a metric size, 210 × 297 mm. Dividing by 25.4 mm per inch gives 8.27 × 11.69 inches, and the pixel figures are rounded to the nearest whole pixel. The length converter is handy for other metric sizes.

Checking a few rows: 5 × 300 = 1500 and 7 × 300 = 2100, and 1500 × 2100 = 3,150,000 pixels. For A4, 8.2677 × 300 = 2480.3 and 11.6929 × 300 = 3507.9, which round to 2480 × 3508. Then 2480 × 3508 = 8,699,840 pixels, or about 8.7 MP.

The megapixel column only works as a quick check if your image already has the right shape. A 12 MP photo has more than enough pixels for an 8 × 10, but because of cropping, the real test is whether both dimensions meet the target after you crop.

Some print services ask for a bleed, a small extra margin around the edge that gets trimmed off. If yours does, add the bleed to the inches before multiplying by PPI.

How much resolution do you actually need?

300 PPI is a rule of thumb, not a requirement. What you need depends on how close people stand to the print. The farther away the viewer, the fewer pixels per inch they can make out.

These ranges are general guidance. Printers, paper types and print services differ, so if a shop publishes its own minimum, follow it. Also, going above about 300 PPI rarely helps a normal print. Extra pixels make the file bigger without visible gain, and the printer driver or print service often resamples the image to its own working resolution anyway.

Sharpness counts as much as pixel count. A blurry or heavily compressed 24 MP photo can print worse than a crisp 8 MP one. If you're saving files for print, a high-quality JPG or a lossless format avoids compression artifacts. The guide to JPG vs PNG vs WebP covers the trade-offs.

Upscaling: what it can and can't fix

If you don't have enough pixels, you can upscale (upsample) the image, but you won't get real detail back.

• Traditional interpolation (bicubic and similar methods) estimates new pixels from the ones around them. It makes edges smoother but softer. The image gets bigger without getting sharper.
• AI upscalers guess at plausible detail, such as hair texture or brick patterns. Results can look convincing, but the added detail is made up. They can also distort faces, text and fine patterns, so check the output closely at 100% zoom.

In practice:

1. Upscaling to hit a number achieves nothing. If the file prints at 220 PPI and the shop's minimum is 200, send it as is. Doubling the pixels won't make the print sharper.
2. A modest upscale can help. Going from 150 to 300 PPI with a good resampling method may give smoother edges than letting the printer stretch the image. How much it helps depends on the image and the software.
3. Large jumps show. Turning a small web image into a poster will look soft or artificial however you resample it. When you can, go back to the original file, rescan the print at a higher scanner DPI, or choose a smaller print size.

The original camera file nearly always has more pixels than copies shared through messaging apps or social media, which often shrink images. Before you upscale, look for that original.

Quick reference before you print

• Check the pixel dimensions, not the DPI tag. That's the number that limits print size.
• Max print size at 300 PPI = width ÷ 300 by height ÷ 300.
• Effective PPI at your chosen size = pixels ÷ inches, for each side.
• Aim for about 300 PPI for prints viewed up close. 150 PPI is a common floor, and large prints viewed from a distance can go lower.
• Crop to the print's aspect ratio first, then check both dimensions.
• If the shop asks for "300 DPI," change the tag without resampling as long as the pixel dimensions already work.
• Add bleed to the dimensions if the printer asks for it.
• Upscale only when you have to, keep it modest, and check faces and text at 100% zoom.
• For screens and the web, don't worry about the DPI tag. Think in pixels and file size.

Frequently Asked Questions

Is 300 DPI the same as 300 PPI?

Strictly speaking, no. PPI counts image pixels per inch and DPI counts printer ink dots per inch. In everyday use, though, print shops and image editors often say "300 DPI" when they mean 300 pixels per inch at the final print size, so you can usually treat the request as a PPI request.

Is a 72 DPI image too low quality to print?

Not necessarily. The 72 is only a metadata label. What matters is the pixel count: a 3600 × 2400 image tagged at 72 DPI still has enough pixels for a 12 × 8 inch print at 300 PPI. You can change the tag to 300 without resampling, and the image itself stays the same.

Does changing DPI make the file size bigger?

Changing only the DPI or PPI value barely affects file size, because the pixels stay the same. File size goes up when you resample to add pixels, or when you save with less compression or in a lossless format.

What DPI should I use when scanning old photos?

For a scanner, DPI sets how many pixels are captured per inch of the original. To reprint a photo at the same size, 300 DPI is a common baseline. If you might enlarge it later, scan higher: a 4 × 6 photo scanned at 600 DPI gives 2400 × 3600 pixels, enough for an 8 × 12 print at 300 PPI.

What PPI should images be for a website?

PPI doesn't really apply on the web. Browsers generally display images by their pixel dimensions, and the resolution tag usually has no effect. Size images to the largest width they'll be displayed at, with extra pixels for high-density screens if needed, and use compression to keep file size down.