Image file size estimator

Why this can only be an estimate

Compressed size depends on the picture, not just its dimensions. A photograph of foliage and a photograph of a clear sky at identical settings can differ fivefold, because JPEG spends bits where there is detail and almost none where there is not. Any tool claiming an exact prediction without seeing the image is guessing and hiding it.

What this does is apply bits-per-pixel figures observed across typical images, adjusted for content type and quality. Expect it to be within about 30% for real photographs, which is accurate enough for planning a page budget or a bulk export, and useless for satisfying a hard upload limit. For that, use the any size compressor, which measures the real bytes rather than predicting them.

One correction to received wisdom, since the numbers here make it visible. People say to use PNG for screenshots, and they are right, but not for the reason usually given. A PNG of a screenshot full of text is typically larger than a JPEG of it, often two or three times larger. You choose PNG anyway because it is lossless: JPEG puts a coloured halo around every hard black edge, which on a page of text is both ugly and permanent. You are paying bytes for fidelity.

PNG only genuinely wins on size when the image has very few distinct colours, which is what the logo option models. A flat two colour icon in PNG can be a fraction of the JPEG, because runs of identical pixels cost almost nothing and JPEG has overhead it cannot avoid.

Common questions