How to Convert MB to KB for a JPEG File

If you need to convert a JPEG image with a size measured in megabytes (MB) to one in kilobytes (KB), there's an easy rule to remember: One megabyte is exactly 1,024 kilobytes, although in some cases, people approximate a megabyte to 1,000 bytes for convenience. If you want to reduce the size of a JPEG file, you can use a variety of image-editing software to do so.

One megabyte is 1,024 kilobytes.
Image Credit: SeanZeroThree/iStock/GettyImages

Simple MB to KB Converter

What's the difference between KB and MB? The terms kilobytes, megabytes, gigabytes and terabytes may seem obscure if you're not familiar with them. After you learn how to convert these units, however, they are easy to work with.

The basic unit is the byte, which is eight binary digits, or bits. Historically, it was the amount of memory used to store one character of English text, and it's a common unit when you're talking about how much random access memory or disk space a particular device has. Many computer programming languages still have features that address memory byte by byte.

The number of bytes a modern computer can store is massive, so people have taken to using larger units to represent storage capacity of chips and drives. Each of the major units is 1,024 times the next smallest unit. This may seem like a strange number, but it's useful in computer science because it is a power of two, meaning it is easily expressible in the binary number system that computers traditionally use. It's also close to 1,000, which is why the computer industry took to using the prefixes that in the metric system are associated with separations by a factor of 1,000.

Specifically, one kilobyte (KB) is 1,024 bytes, one megabyte (MB) is 1,024 kilobytes, one gigabyte (GB) is 1,024 megabytes, and one terabyte (TB) is 1,024 gigabytes. If you have a particular number of megabytes of data in a JPEG file or any other type of digital file, you can multiply by 1,024 to find the size in kilobytes. A 2 MB image is the same size as a 2,048 KB image. In rare cases, especially in some advertising contexts, the units may be used to represent differences by factors of 1,000 rather than 1,024.

Image Sizes and Photo Quality

Typically, digital image files with higher resolution and greater detail are larger than their lower-resolution cousins. That's because they need more storage space to store all that detail. JPEG files, an image format named for the Joint Photographic Experts Group that developed it, are no exception. They also use what is called lossy compression to reduce the size of photos and make them easier to send across the internet quickly. That means that they remove some detail from the photo in ways various algorithms estimate is unlikely to impact image quality.

Depending on what you're doing with an image, you may opt for higher quality or smaller file size. If you're going to use a photo to print a large poster, you want greater detail than you would for a thumbnail image on a website. For online images, you also want to take into account how speedy you expect people's internet connections to be when they need to access the photos.

Adjusting Image File Sizes

Most image editing software gives you the option to adjust a photo's size. This is true of professional software like Adobe Photoshop and the open-source tool called GIMP, as well as free software that comes with operating systems, such as Microsoft Paint on Windows, Apple Preview on macOS, and the gallery software on modern smartphones. In most cases, you open the image in the software, which displays the current size or dimensions, and then you specify a smaller size. Some data is lost when you resize an image to make it smaller.

Think about how you're going to be using a photo and adjust the size accordingly. It's often worth trying several sizes and seeing how they look in the desired medium, whether that's on a big or small screen or a piece of paper.

After you reduce an image size, it's usually not worth trying to increase the image size in KB again, because the data has already been removed from the photo. For that reason, it's a good idea to keep an unedited version of a photo around in case you want to experiment with different sizes later on.

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