What are megapixels?

Cover photo by Amal S on Unsplash

If you’ve been looking at cameras to buy a key advertised specification is the number of megapixels the camera has. Megapixels is literally two words stuck together, “mega” and “pixels”. What do mega and pixels have to do with camera sensors? Well, the word “mega” is Greek for “large” or “great”. This Greek word “mega” is used in the metric system to denote “1 million”. If you have a mega amount of something such as a megaton, or megawatt, those values equate to 1 million tons and 1 million watts. So a megapixel works the same way, it literally means 1 million pixels.

Pixel is the other part of the word megapixel, so what is that exactly? The pixel is a fundamental concept in computing. It is a way of displaying images that is used in almost all digital imaging devices. The pixel is necessary in order to convert an image from being analog to being digital. This conversion process is called “quantization”.

A common misconception of pixels is that they have a size. While a pixel may appear very small on your phone screen or monitor, by definition pixels have no specific size. Generally, pixels are small because our eyes don’t like to see pixels, smaller pixels tend to help images look more real to us when seen on screens. In an image file such as jpeg or what have you, pixels are pretty much nothing but a color value or brightness level with no dimension. Inside of a camera or a computer monitor, each pixel is given its value by the image file. By combining lots of pixels together, each with their own color value, an image you can recognize can be formed from those values on a computer screen or inside of the camera.

Since pixels have no size if you want a larger image of something you need MORE pixels. Increasing the size of the pixels doesn’t technically increase the spatial resolution. However, some displays do use very large pixels such as jumbo screens in stadiums or those used for electronic billboards on the side of the highway. These very large screens are viewed from so far away that a larger pixel is used. This makes building those kinds of screens much easier, and since the viewers are far away its hard to tell that the pixels in the screen are actually really big.

Pixels in personal computing devices are generally very small and numerous, sometimes too small to see with the naked eye. This is because personal computers such as desktops and phones are viewed relatively closeup. At these distances our eyes are capable of seeing very fine details which is why the pixels in your phone screen have to be really small.

A common example would be a computer monitor or television that has a resolution of 1,920 by 1,080. This resolution number means the monitor/TV displays a grid of pixels that is 1,920 pixels wide, and 1,080 pixels tall.

If you’re familiar with how to get the area of a rectangle, finding the number of pixels works exactly the same way. Simply multiple the two sides together and that gives you the number of pixels contained within our rectangle of pixels.

In the case of 1,920 by 1,080 screen, multiplying the two numbers together gives 2,073,600. That is two million, seventy three thousand, and 600 hundred pixels in total. Going back to our other word part “mega” you would write the resolution of the monitor out as 2 megapixels.

Most modern phone screens have a resolution around 2-4 megapixels.

A list of some common screen sizes and their megapixel value is shown below:

Resolution	Megapixels
1080p (1920 x 1080 FHD)	2.07 Megapixels
1440p (2560 × 1440 WQHD)	3.69 Megapixels
2160p (3840 × 2160 4K UHD)	8.30 Megapixels
4320p (7680 × 4320 8k UHD)	33.20 Megapixels
15360 x 8640 (16k)	132.71 Megapixels

There aren’t a lot of screens supporting 16k resolution out there, but such setups do exist. The highest officially supported standard by the TV industry is 8k UHD or 8k DCI (for theaters) and that tends to be the maximum for video cameras as well. Only a handful of cameras can film in 8k. Higher resolutions are possible but not realistic at this point in time. For most viewing purposes such as TV’s and theater screens, 8k is more than enough pixels to produce a realistic image where the actual pixels are invisible to the eye. In fact, the majority of digital movie screens are still only at 1080p resolution, and most films still target 1080p as their distribution resolution. Yep, much of the time when movies are advertised as 4k those have been up-sampled to that resolution, not actually produced in that resolution.

Pixels are pretty simple once you understand what they are. Depending on what your goals are, if you’re making movies for example, a 4k camera should be good for you.

Print resolution is another matter entirely and is much more resolution intensive. For a variety of reasons, it turns out that movies don’t really need all that much resolution as much as movie makers want to pretend they need it. Prints do actually need large resolution figures because 300dpi is generally seen as the standard resolution for prints and has been the standard for many years. 300dpi stands for “dots per inch”. Which means that in one square inch of the final print there should be 300 x 300 pixels of resolution.

Below is a chart showing some common print resolutions and their associated megapixels requirement.

Print Size	Megapixels
4″ x 6″	2.20 Megapixels
5″ x 7″	3.20 Megapixels
8″ x 10″	7.20 Megapixels
16″ x 20″	28.80 Megapixels
24″ x 36″	77.80 Megapixels

Maintaining 300 dpi resolution at print sizes above this probably isn’t necessary in most cases as the viewing distances tend to be greater with really big prints. This means you can easily come down to 200×200 dpi or simply upscale a 200 dpi image to 300 dpi before printing it out.

As you can see the resolution required for large prints shoots upward rapidly. But 99% of the ways that normal people view photos will fall under the resolution for 8k monitors which is 33.20 megapixels. Only in some rare instances such as printing for art galleries or clients who want extremely large prints for display would any photographer need more than 33.2 megapixels.

What a wild ride through the megapixel gauntlet. We learned about Greek, we learned about the metric system, we learned that pixels are dimensionless color values, and we learned about video and print resolution, wow, now you have some great information to make a better buying decision on your next camera.