Megapixels and Megabytes Explained

Do you find yourself struggling to understand the difference between megapixels and megabytes when it comes to your photos? You’re not alone. Let’s see if we can figure this out without a lot of scientific jargon.

Megapixels and megabytes determine the image size and file size of the photos you take. Most of the time, you don’t even think about this. You just load a memory card into your camera and shoot away. 

However, if you try to enter a photo contest or send a photo to a magazine, newspaper, or TV station, you’ll suddenly find yourself bombarded by requirements that seem to make no sense. And what about trying to send a group of photos in the same email? You may have no success at all.

Do your camera settings make a difference?

Let’s start here. When I teach my Camera Mechanics Workshops, I always tell my students to set their digital cameras to take the largest size and highest quality images available on their cameras. You can always downsize the image later in post-processing, but you want to capture as much detail as possible when you are shooting. 

If you follow this advice, each of the photos taken with your DSLR or mirrorless camera will have the same image size.

Both photos above were shot with the same camera and have the same number of megapixels. They were both shot in the RAW format. The file size of the photo of the scarves is 30.45 megabytes. The lighthouse photo has a file size of 27.20 megabytes.

(Quick note: If you shoot with an iPhone instead of a DSLR or mirrorless camera, you’ll discover that you can change the dimensions of your photos. You can set your iPhone to shoot a regular rectangular photo (4:3), a square photo (1:1), or even a long and skinny one (16:9). This will result in different image sizes since the length and width have changed. I’ll write more about that in a future post.)

But how is the image size measured?

Megapixels and image size

This is where megapixels come in. We’re all familiar with them since manufacturers use them in advertising. When a new camera model is introduced, the megapixels are always highlighted. For many years, as the number of megapixels increased from model to model, this was a big step forward. More megapixels meant you could print your photo larger while maintaining high quality.

But what is a megapixel? Digital photos are made up of pixels, millions of them. This is where the colors and details of your photo are stored. As you increase the number of pixels, you also increase the amount of detailed information that can be stored. One megapixel is simply one million pixels.

Your image size is found by multiplying the length of the photo by the width, measured in megapixels. My Canon 5D Mark IV takes a photo that measures 6720 x 4480 megapixels. When you do the multiplication, it shoots a 30-megapixel photo.

Megapixels: Does it matter if you are shooting Raw or JPG?

This one’s easy to answer. No. If your camera shoots 30-megapixel photos, that’s what it shoots. The image size is 30-megapixels. Just remember to leave the camera set to maximum size. 

But you’ve heard that RAW photos are much larger than JPGs. I think that this is where it gets confusing. 

When you take a photo, the camera gathers all the details of the scene. It records the lights and darks, the highlights, and the shadows, plus all the colors. That is what a RAW photo is. And it’s all stored in the pixels. 

So, you don’t end up with more megapixels if you shoot in RAW. You just end up with more information stored in the ones you have. 

Likewise, you don’t end up with fewer megapixels if you shoot in JPG. You just end up with less information stored in the pixels. 

Will cropping your photo in post-processing affect the image size?

Yes. When you crop your photo, you’re cutting off and discarding parts of it, so you will have less megapixels.

Megabytes and file size

Now we get to the other measurement, file size. Where do we start?

I love a good analogy, so let’s start there. Imagine for a minute that your 30 megapixels are 30 boxes neatly stacked in your attic. If you put two shoes in each box, you can store 30 pairs of shoes. 

Of course, you could put four shoes in each box, and you would now have 60 pairs of shoes! You have increased the number of shoes you can store without changing the number of boxes.

Just to quickly tie this into photography, the shoes are the colors and details captured by your camera when you take a photo. The boxes are the megapixels, and the attic is your camera sensor. 😎

Now, let’s move to an apartment with a large closet and no attic. You are going to put the shoes away. As you open the boxes, you neatly place the shoes on the closet shelves (aka the memory card in your camera).

If you only stored two shoes in each box, you have plenty of room for them. When you are finished, you have three shelves with shoes on them. You might say that your “shoe/file” size is three shelves. 

But what if you stored four shoes in each box? They will take up much more space in your new closet. In fact, you may be looking for more storage. Your “shoe/file” size is two times larger! (This is when you head to Amazon.com to order more shelves or to order an external hard drive for your photos! 😉)

Can you see how the number of boxes or megapixels isn’t related to the shelves or file sizes?

Now let’s look at a few photos to illustrate this point. 

While this photo of a crumpled white sheet does have some detail in the shadows and highlights, it has almost no variation in color. It was taken with my iPhone 13 Pro and has an image size of 12 megapixels. Its file size is 4.7 megabytes. 

Now, here’s a shot taken with the same camera. I’ve bunched up the cloth to add shadows and highlights. On top of that, there’s lots of color in the flowers. While the image size is still 12 megapixels, the file size is now 5.2 megabytes. In other words, I stored more color and detail in the same number of megapixels! 

So, your image size is going to be the same from photo to photo if you’re shooting with the same camera. (iPhone note: If you change the dimensions of your photo before you shoot, this may not be true.) On the other hand, since your file size is going to reflect how much color and detail you captured and stored in the image, it will vary.

I know I’ve really simplified this explanation, and I hope that helps you gain an understanding of the difference between the two ways of measuring a photo. There is also more information stored in the file such as the date and time when the photo was taken and the details of the camera you used. 

Now it’s your turn to experiment with megapixels and megabytes.

Why not set up your own experiment? Take a series of photos with the same camera and see how much the file size varies. If you have an Apple computer, you can discover the number of megapixels and the file size by clicking on the “i” in the circle at the top of the page in the Photos app. On your iPhone, you’ll find the information by sweeping up with your finger while you’re looking at the photo. 

For more information about storing and backing up your photos, you can read this post. https://www.carolinemaryan.com/back-up-your-photos/

This article goes into more detail about what sizes you need to know for submitting a photo to galleries and contests. https://arthousehq.com/makes-file-right-size-job/

Sony gives a good explanation of file size and image size in this article. https://www.sony.com/electronics/support/articles/00010755