Estimate an image file's size from its resolution, bit depth, and compression level.
Calculator verified • Last updated: August 2026
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Compression ratios are rough typical estimates — the real file size depends heavily on the image's actual content, not just its resolution and format.
An uncompressed image stores a fixed number of bits for every pixel. Multiplying width by height gives the total pixel count, multiplying that by the bits-per-pixel color depth gives the total bits, and dividing by 8 converts bits to bytes — the uncompressed file size. Real-world image formats then apply compression, which this calculator approximates by dividing the uncompressed size by a typical compression ratio for the selected format.
$$\text{Size} = \frac{W \times H \times B}{8 \times R}$$
W: image width, in pixels.
H: image height, in pixels.
B: bits per pixel (color depth).
R: typical compression ratio for the selected format.
A 1920x1080 image at 24-bit RGB, uncompressed: 1920 times 1080 times 24, divided by 8, equals about 6,220,800 bytes, or roughly 6.1 megabytes. Saved as a typical PNG (compression ratio around 3x), the estimated size drops to about 2.03 megabytes; saved as a high-quality JPEG (ratio around 10x), it drops further to about 622 kilobytes.
Actual compression depends heavily on image content, not just resolution and format. A photo with large areas of flat color or gentle gradients (a clear sky, a plain background) compresses far more than a busy, highly detailed photo (dense foliage, fine texture) at the same resolution and format — real files can land noticeably above or below this estimate depending on what's actually in the picture.
Confusing bits and bytes is a frequent source of error — file sizes are conventionally reported in bytes (and KB/MB built from bytes), but color depth is specified in bits per pixel, so the division by 8 is essential and easy to accidentally skip.
Assuming JPEG and PNG compress by the same ratio is another — PNG's lossless compression typically achieves a much smaller reduction than JPEG's lossy compression, so swapping the compression option without changing the format assumption can produce a very misleading estimate.
Bit Depth (Bits per Pixel) — how many bits are used to store the color of a single pixel; higher bit depth allows more distinct colors but takes more space.
Lossless Compression — a compression method (like PNG) that shrinks a file without discarding any image data, so the decompressed image is identical to the original.
Lossy Compression — a compression method (like JPEG) that discards some image detail, usually detail less noticeable to the eye, to achieve a much smaller file size.
Multiply width in pixels by height in pixels by the bits used per pixel, then divide by 8 to convert bits to bytes. A 1920x1080 image at 24-bit color, for example, is 1920 x 1080 x 24 / 8, or about 6.2 megabytes uncompressed.
Most image formats apply compression, which removes redundant or less-noticeable data before saving. This calculator divides the uncompressed size by a typical compression ratio for the selected format, but real compression ratios vary a lot depending on the image's actual content — a photo of a busy forest compresses less than a photo of a clear blue sky.
PNG uses lossless compression, meaning no image data is discarded, which typically yields a smaller size reduction than JPEG. JPEG uses lossy compression, discarding some visual detail that's less noticeable to the eye, which achieves a much smaller file size at the cost of some (adjustable) quality loss.