Image Resolution and DPI Explained for Beginners

What resolution actually means

A digital photo is a grid of tiny squares called pixels. A photo that is 3000 pixels wide and 2000 pixels tall has 6,000,000 of them, which is where the figure "6 megapixels" comes from. That pixel count is the photo's real resolution. Everything else in this guide follows from it.

Two other terms cause most of the confusion:

• PPI (pixels per inch) describes how many pixels are packed into each inch when an image is displayed or printed at a particular size.
• DPI (dots per inch) strictly describes the dots of ink a printer lays down. In everyday use, and in many software dialogs, people say DPI when they mean PPI. For editing purposes you can treat them as the same thing.

The important point is that PPI is not stored in the pixels. It is a label that says "print this many pixels per inch", and it only means something once you decide on a print size.

The one calculation you need

Pixels needed = print size (inches) × PPI. A 4 × 6 inch print at 300 PPI needs 1200 × 1800 pixels. Going the other way, divide your pixel dimensions by the PPI you want to see how large you can print: a 3000 × 2000 photo at 300 PPI prints at 10 × 6.7 inches.

How many pixels for common print sizes

Print labs and printers may quote their own recommended values, so check the lab's requirements before you order a large print.

Step by step: check and set size in Photoshop

1. Read the pixel dimensions.

   The Image Size dialog shows width and height in pixels. This is your photo's true resolution.

2. Change print size without changing pixels.

   Untick Resample. Now type 300 into Resolution and watch Width and Height (in inches) update. Nothing was added or removed; only the label changed. This tells you how large the photo can print at 300 PPI.

3. Only resample if you must.

   With Resample ticked, Photoshop makes new pixels or discards existing ones. Reducing size is usually safe. Enlarging invents pixels (see the next section).

4. Work on a copy.

   Resample a duplicate, not your master file. Use File > Save As with a new name.

Enlarging a photo: what is and is not possible

If a photo has too few pixels for the size you want, software can enlarge it by calculating new pixels between the existing ones. This is called resampling or upscaling. It can make an image smoother, and AI-based tools can add plausible-looking texture, but none of them can recover detail that was never captured.

It is better to start with enough pixels. If you are scanning a print, see the scanning guide for how to capture the most detail.

What about "72 DPI for the web"?

You will often read that web images must be 72 DPI. This is a myth. Browsers display an image according to its pixel dimensions; the PPI value stored in the file is ignored. A 1200 × 800 pixel image looks identical on a web page whether it is labelled 72 or 300 PPI. What matters for the web is pixel size and file size: use dimensions near what the page actually displays, and a sensible JPEG quality (see the format guide).

Worked example: prepare a photo for an 8 × 10 print

Imagine the original is 3000 × 2000 pixels and the print lab asks for an 8 × 10 inch portrait. Do not change the resolution field first. Work through the crop and pixel requirement in this order:

1. Check the original dimensions. The file is 3000 pixels wide by 2000 high, so it has enough pixels for many medium prints, but its landscape shape does not match an 8 × 10 portrait.
2. Choose the crop before resizing. An 8 × 10 print has a 4:5 aspect ratio. Crop to that shape, keeping the important subject away from the edges. A portrait crop from the original will discard substantial width; inspect the crop preview rather than assuming all 3000 pixels remain available.
3. Check the cropped pixel dimensions. A 4:5 crop from a 3000 × 2000 image can be no larger than 1600 × 2000 pixels without adding pixels. At 300 PPI, an 8 × 10 print needs 2400 × 3000 pixels, so this crop does not contain enough native pixels for that target.
4. Decide whether the print is still suitable. At 200 PPI, 1600 × 2000 pixels produces an 8 × 10 inch print. That may be perfectly acceptable at normal viewing distance. Ask the lab whether it accepts 200 PPI before enlarging.
5. Only upscale if the output requirement justifies it. If the lab insists on 300 PPI, resampling can create a 2400 × 3000 file, but it cannot restore genuine detail that was not captured. Inspect eyes, hair, fine patterns and edges at 100% after enlargement.
6. Save a separate print copy. Keep the original untouched, retain your layered working file, and export a copy using the lab's requested colour profile and format.

This example shows why a single DPI number cannot answer whether a photo is printable. The crop, actual pixel dimensions, viewing distance and printer requirements all matter. If the subject is too close to the edge, choose a smaller print rather than sacrificing an important part of the photograph just to hit a number.

Common mistakes

• Raising the PPI number and expecting more detail. With Resample off, the pixels do not change. With Resample on, you are guessing new pixels.
• Judging by file size. A large file is not necessarily high resolution; it can be heavily compressed or padded. Check the pixel dimensions.
• Using a screenshot or a messaging-app copy. Social and chat apps usually shrink photos. Ask for the original file.
• Ordering a print from a thumbnail. Compare your pixel width with the table above before ordering.

Key takeaways

Next, learn which file format to save in.