What a megapixel is
One megapixel is one million pixels. Multiply the width by the height and divide by a million: a 4000x3000 image is 12 megapixels.
It describes how many samples of the scene the sensor recorded. It says nothing about how good those samples are — sensor size, lens quality, and light have far more influence on how a photo looks than the pixel count does.
That is why a 12-megapixel photo from a good camera in good light beats a 48-megapixel photo from a small sensor in a dim room, comfortably and obviously.
What screens actually display
Every common display target, converted to megapixels:
- 1080p full HD screen: 2.1 MP
- 1440p monitor: 3.7 MP
- 4K screen: 8.3 MP
- Typical phone display: 2.5 to 3.5 MP
- Instagram feed image at 1080x1350: 1.5 MP
- Full-width website hero at 2000 pixels wide: about 2.5 MP
The implication for web use
If an image is only ever going to be looked at on a screen, anything beyond about 8 megapixels is stored for no reason. Most web images need 2 to 3.
A 48-megapixel phone photo destined for a website is carrying roughly twenty times the pixels the page will use. The rest is bandwidth, storage, and processing time spent on data that gets discarded before display.
This is the single most common inefficiency in web images and the easiest to fix. Resize to the display size before doing anything else.
What printing needs
At 300 DPI, the standard for images held at reading distance:
- 6x4 inch photo: 2.2 MP
- 7x5 inch: 3.2 MP
- 10x8 inch: 7.2 MP
- A4: 8.7 MP
- A3: 17.4 MP
- A2 poster at 150 DPI (viewed from further away): 8.7 MP
Viewing distance changes everything
The 300 DPI standard assumes something held about 30cm away, which is roughly the limit of what the eye resolves at that distance. It is not a universal requirement and treating it as one produces enormous files for no benefit.
Double the viewing distance and you can halve the resolution with no perceptible difference. A poster on a wall viewed from two metres is fine at 150 DPI. Billboards are routinely printed at 30 DPI or less.
This is why a large print does not necessarily need a huge file. An A2 poster viewed from across a room needs about the same pixel count as an A4 held in the hand.
Where extra megapixels genuinely help
Cropping. If you shoot wide and crop to a quarter of the frame, you keep a quarter of the pixels — so a 48-megapixel capture cropped hard still yields 12. That is the strongest argument for high resolution and it is a real one.
Large prints viewed closely, such as gallery work.
Archival copies, where you do not yet know what the image will be used for and cannot go back and re-shoot.
Some computational photography modes that combine multiple high-resolution frames into one better low-resolution result — there the megapixels are an intermediate, not the output.
Where they actively cost you
Storage and backup, obviously, and it compounds across a library of thousands of photos.
Low-light performance. On a fixed sensor size, more pixels means smaller pixels, and smaller pixels collect less light each. That is why many phones bin four or nine sensor pixels into one output pixel in dim conditions, deliberately producing a lower-resolution but cleaner image.
Processing time, upload time, and failed uploads on poor connections.
Every downstream step. Editing, resizing, and compressing all take longer on files several times larger than anything needs.
A sensible policy
Shoot at a high resolution if the camera offers it and storage is not a constraint, because you cannot add pixels later and cropping room is genuinely useful.
Export at the resolution the destination needs, which is almost always far lower. One master, many exports.
For web use, that means 2 to 3 megapixels. For a standard photo print, 3 to 8. For social media, under 2. Anything beyond that is being downloaded and thrown away by whoever receives it.
Frequently asked questions
How many megapixels do I need for a website?
Two to three for most images. A 4K screen only displays 8.3 megapixels in total, and a typical content image occupies a fraction of that.
How many megapixels for a 10x8 print?
7.2 at 300 DPI. A4 needs 8.7. Larger prints viewed from further away need proportionally fewer.
Is a 48 MP phone camera better than a 12 MP one?
Not necessarily. Sensor size, lens quality, and light matter more. Many high-megapixel phones combine sensor pixels in low light, outputting a cleaner lower-resolution image on purpose.
Do more megapixels mean better quality?
They mean more samples, not better ones. Beyond what the destination displays, extra megapixels cost storage and low-light performance without improving anything visible.
When are extra megapixels worth it?
Cropping room is the strongest reason — crop to a quarter of the frame and you keep a quarter of the pixels. Also large prints viewed closely, and archival copies.
What resolution should I export for social media?
Under 2 megapixels. Instagram serves 1080 pixels wide, which is about 1.5 MP for a portrait post.