Image File Size Estimator
Estimate how big an image file will be from its dimensions, colour depth, and format — raw bitmap and a compressed JPEG, PNG, or WebP estimate.
From pixels to bytes
Every pixel stores colour using a fixed number of bits, so the raw size of an image is pure arithmetic: pixels times depth. Compression is where formats diverge — lossy JPEG and WebP trade a little detail for a much smaller file, while lossless PNG keeps every pixel exact but stays larger. Knowing the rough size ahead of time helps with upload limits, page-weight budgets, and storage planning.
The pixel count comes straight from the dimensions — work it out with the Megapixels & Resolutioncalculator — and if you’re shrinking an image to cut its size, the Image Resize Calculator shows the new dimensions.
Frequently Asked Questions
How is the raw (uncompressed) size worked out?
Multiply width × height to get the pixel count, then multiply by the colour depth in bits per pixel and divide by 8 to get bytes. A 1920×1080 image at 24-bit RGB is 1920 × 1080 × 24 ÷ 8 = 6,220,800 bytes, about 5.9 MB. That is the fixed bitmap size before any compression.
Why is the estimated file so much smaller than the raw size?
File formats compress the bitmap. JPEG and WebP are lossy and can shrink a photo to roughly a tenth of its raw size or less; PNG is lossless and typically lands around half; BMP and TIFF are effectively uncompressed. This tool multiplies the raw size by a typical ratio for each format to estimate the saved file.
How accurate is the estimate?
It's a ballpark, not a guarantee. Real compressed size depends heavily on image content — a flat sky compresses far more than fine foliage — and on the quality setting you choose. Use the estimate to compare formats and plan storage or upload budgets, then check the actual file once exported.
What colour depth should I choose?
24-bit (RGB, 8 bits per channel) covers most photos. Choose 32-bit if the image has an alpha (transparency) channel, 8-bit for grayscale, and 48-bit for 16-bit-per-channel files from raw editing. Higher depth means a larger raw bitmap and usually a larger saved file.
Educational estimate only. Compressed size varies widely with image content and quality settings; the raw bitmap figure is exact.