Image Size Checker

The four numbers a file has

Every image has a width and height in pixels, an aspect ratio derived from them, a format, and a file size in bytes. They are related but they are independent, which is the source of most confusion. A large file can have few pixels, as with an uncompressed TIFF. A small file can have many, as with a well compressed AVIF. And two images with identical dimensions can differ ten times over in file size depending entirely on how they were encoded.

Turning dimensions into a print size

The single most useful thing to do with a pixel count is work out how large it can print. Divide the pixel dimensions by the target resolution, and the result is the largest print that looks sharp at that resolution. This is why a megapixel figure alone is not enough: 12 megapixels at 300 DPI gives a specific maximum size, and the same 12 megapixels at 150 DPI gives exactly twice that, with less visible detail.

NoteUse the print size calculator for the precise answer. The table assumes full width is the long side.

Why a file can be large with few pixels

File size comes from how the image is encoded, not from how many pixels it has. An uncompressed TIFF stores every pixel at full size, so a 24 megapixel scan can be 70 MB. A JPG discards most of the detail, so the same pixels might be 8 MB. A well compressed AVIF might be 1.5 MB. This is why a large file does not necessarily mean a large image, and why a large image is not a quality problem. It is an encoding problem, and it is usually fixable by converting rather than by resizing.

• Uncompressed TIFF: very large, lossless, for print and archive.
• PNG: large, lossless, for graphics and transparency.
• JPG: moderate, lossy, the universal delivery format.
• WebP or AVIF: small, lossy, best for the web.
• A large file with few pixels means the format, not the dimensions.

Checking against a platform requirement

The common use for this information is checking an upload before attempting it, rather than after a rejection. A platform that wants a square image, a specific pixel count, or a maximum file size will usually state all three, and a file that satisfies one and not another is still rejected. Checking first turns a failed upload into a quick resize, which is why reading four numbers takes less time than the upload cycle it saves.

• Check dimensions, aspect ratio, and file size before uploading.
• A file meeting one requirement can still fail another.
• Resize for a dimension requirement. Convert for a file size one.
• Some platforms validate the extension, so the format matters too.