Megapixels, PPI and DPI explained
Updated 13 October 2026 · UnBlur AI guides · 8 sources
AI results are estimates. AI restoration predicts what a sharper or repaired photo might look like. It can invent or change details, especially faces, text and fine patterns. Always keep your original, and do not use an AI-restored image as evidence or to identify someone.
- Megapixels count the pixels in an image: width × height ÷ 1,000,000. They say nothing about whether the photo is sharp.
- PPI (pixels per inch) describes how densely pixels are spread over a print or screen; DPI properly describes a printer's ink dots, though scanners use DPI for the same idea. 1,2
- About 300 ppi is a common target for prints viewed up close. 1
- Digital zoom crops and enlarges the image, so it adds pixels without adding optical detail. 3
Megapixels tell you how many pixels a photo has. PPI tells you how tightly those pixels are packed when the photo is printed or shown on a screen. DPI is a printer's measure of ink dots, although scanner software uses it to mean the same thing as PPI. Once you see how the three connect, it becomes easy to work out how big you can print a photo and why a "high-megapixel" image can still look blurry.
Megapixels: the pixel count
A digital photo is a grid of pixels. Multiply the width by the height and divide by a million to get megapixels (MP). A 4032 × 3024 photo has about 12.2 million pixels, so it is called 12 MP. The number is about quantity, not quality. A blurry, noisy or heavily compressed 12 MP photo still has 12 million pixels; many of them just do not carry useful detail.
| Megapixels (4:3 shape) | Approximate pixel size | Sharp print at 300 ppi |
|---|---|---|
| 1 MP | 1155 × 866 | about 3.9 × 2.9 in |
| 3 MP | 2000 × 1500 | about 6.7 × 5 in |
| 12 MP | 4000 × 3000 | about 13.3 × 10 in |
| 24 MP | 5660 × 4240 | about 18.9 × 14.1 in |
| 48 MP | 8000 × 6000 | about 26.7 × 20 in |
The sizes are rounded arithmetic for a 4:3 photo. On supported iPhones the main camera saves 24 MP photos by default (you can switch to 12 MP), and it can capture 48 MP when you turn on Resolution Control or ProRAW & Resolution Control in Settings > Camera > Formats 4. For ProRAW, Apple notes that only photos taken with the main camera at 1x can be saved at 48 MP; Ultra Wide, Telephoto, Night mode, flash and macro photos can only be saved at 12 MP 5.
PPI: pixels per inch
A file has no physical size until you print or display it. PPI is the bridge: it says how many of the file's pixels fit in one inch of paper or screen. The arithmetic is the same in both directions:
- Print size = pixels ÷ ppi. A 3000-pixel side at 300 ppi prints 10 inches long.
- Pixels needed = inches × ppi. A 6 × 4 inch print at 300 ppi needs 1800 × 1200 pixels 6.
For printing, about 300 ppi is the usual target; Binghamton University Libraries add that going above roughly 600 ppi only makes files bigger, because the eye will not see the difference 1. Prints that hang on a wall and are seen from a few feet away can use less. The full table for common print sizes is in upscaling a photo for print.
The ppi value stored inside a file (the "72 ppi" or "300 ppi" you may see in an editor) is just a label. Changing it without resampling changes the suggested print size, not the detail.
DPI: dots per inch
Strictly, DPI describes output: how many ink or toner dots a printer lays down per inch. Printers use several tiny dots of different inks to reproduce each pixel's color, so a printer's DPI is usually much higher than the image's PPI. Binghamton's guide points out that the terminology switches to DPI when printing, and that DPI refers to the printer's output resolution 1.
Scanners muddy this. A Library of Congress guide to scanning notes that image specialists prefer the precise term pixels per inch, but scanner software almost always says DPI, so it uses DPI too 2. When a scanner asks for "600 dpi", it means 600 pixels for every inch of the original. See how to scan old photos properly for the settings to use.
Why more pixels do not always mean a sharper photo
- Blur. Camera shake, subject motion and missed focus smear detail across many pixels. See motion blur vs focus blur.
- Digital zoom. Zooming past a lens's optical range crops the image and scales it back up, so no optical resolution is gained 3. Apple's specifications list optical-quality zoom ranges separately from the much larger digital zoom figures for each iPhone 7.
- Compression. Messaging apps often shrink and recompress photos; see why photos look blurry after you send them.
- Upscaling. Enlarging a small image makes more pixels, but interpolated pixels are guesses from their neighbors, so the result is bigger but fuzzier 6.
Where AI tools come in
AI upscalers and deblurring apps can return images with more pixels or crisper edges, but the extra detail is predicted from patterns the model learned, not measured from the scene 8. UnBlur, for example, returns about one megapixel in its standard modes and up to 2048 pixels per side (about 4 megapixels) in Ultra HD. That is enough for screens and small prints. Judge any result by how it looks at the size you will use, not by its pixel count alone, and keep your original. More on this in what AI restoration can and can't do.
Common questions
Is a 48 MP photo four times sharper than a 12 MP one?
It has four times as many pixels, which helps for cropping and big prints, but only if the photo is in focus, steady and well lit. For ProRAW, Apple notes that some shots, such as Night mode, flash and macro, can only be saved at 12 MP. 5
Should I save photos at 300 dpi for the web?
The dpi or ppi label does not matter on screens; only the pixel dimensions do. Use pixel size to decide, and keep the full-size original for printing. 1
What does 600 dpi mean on a scanner?
It means the scanner records 600 pixels for every inch of the original, so a 4-inch-wide print becomes 2400 pixels wide. Scanner software uses dpi where image specialists say ppi. 2
Sources and further reading
- Binghamton University Libraries. Digital Imaging - Using Images (subject guide). libraryguides.binghamton.edu
- Library of Congress, The Signal blog. Personal Digital Archiving: The Basics of Scanning (2014). blogs.loc.gov
- Wikipedia. Digital zoom. en.wikipedia.org
- Apple Support. Change advanced camera settings on iPhone. support.apple.com
- Apple Support. About Apple ProRAW. support.apple.com
- Vanderbilt University Center for Teaching. What Resolution Should Your Images Be? (PDF). cft.vanderbilt.edu
- Apple Support. iPhone 17 Pro Max - Tech Specs. support.apple.com
- Ledig C, et al. Photo-realistic single image super-resolution using a generative adversarial network. IEEE CVPR. 2017. arxiv.org