Image Compression Calculator

What Is an Image Compression Calculator?

An Image Compression Calculator compares the size of an image before and after compression. It calculates the amount of storage saved, the percentage reduction in file size and the compression ratio between the original and compressed files.

This can be useful when optimising images for websites, applications, online stores, documents and other digital projects. Web developers, designers, SEO professionals, content creators and website owners can use the results to understand the effect of image compression without manually performing the calculations.

Why Use an Image Compression Calculator?

Comparing image file sizes makes it easier to measure the practical effect of compression and understand how much data has been removed from an image file.

How to Use the Image Compression Calculator

Enter the file sizes before and after compression, then review the calculated compression results.

1. Enter the original image size — Enter the file size before compression and select the appropriate unit.
2. Enter the compressed image size — Enter the size of the image after compression and select its unit.
3. Calculate compression — Select the Calculate Compression button to process the two file sizes.
4. Review the results — Check the amount saved, percentage reduction, compression ratio and remaining file size.

How to Calculate Image Compression

Image compression can be measured by comparing the original file size with the size of the compressed image. The difference between those two values represents the amount of storage saved. The percentage reduction shows how much smaller the compressed file is relative to the original.

For example, if an image originally measures 4 MB and compression reduces it to 1 MB, the image has saved 3 MB of storage. The file size reduction is 75%, and the compression ratio is 4:1 because the original file is four times the size of the compressed file.

Image Compression Percentage Formula

The percentage reduction is calculated using the original image size and compressed image size. The formula is: ((Original Size − Compressed Size) ÷ Original Size) × 100. A higher percentage means a larger reduction in file size.

Image Compression Ratio Formula

The compression ratio is calculated by dividing the original file size by the compressed file size. For example, a 5 MB image compressed to 2 MB has a compression ratio of 2.5:1. The ratio describes the relationship between the two file sizes rather than directly describing image quality.

Understanding Image Compression Results

A reduction in file size does not automatically indicate how much visual quality has been lost. Lossy compression can produce substantial file-size reductions by removing image information, while lossless compression preserves the original image information but may achieve a smaller reduction.

The most appropriate compression level depends on how an image will be used. Website images often need to balance file size, dimensions, format and visual quality. A smaller image can reduce the amount of data required to load a page, but excessive compression may introduce visible artefacts or reduce detail. The calculator measures file-size changes only; it does not assess image quality or determine whether a particular compression level is suitable.

Frequently Asked Questions