Compress Images to 150KB

Where 150KB is the right number

A 150 kilobyte budget is small, and small budgets usually come from a specific constraint rather than a preference. Avatars and thumbnails, email inline images, and form fields that are part of a larger submission all land in this range. It is also the size where the choice of format and dimensions starts to matter more than the quality slider, because at this budget a poorly prepared image looks bad while a well prepared one does not.

At this size, dimensions decide quality

Compression removes detail. Resizing removes pixels. At a 150KB budget on a large image, compression has to remove a great deal of detail and the result is soft. Resizing to a sensible size first means each remaining pixel gets a larger share of the budget, and the image looks sharper at exactly the same file size. This is the single most useful thing to understand about tight limits: prepare the dimensions, then let the compressor spend the remaining budget on quality.

• For a thumbnail, resize to roughly 400 pixels before compressing.
• For an avatar, resize to 200 to 400 pixels. Going larger wastes budget.
• For a form field, check whether the form displays the image small, and resize to that.
• Only compress a full resolution image to 150KB when full resolution is actually required.

NotePreparing the size first is almost always the better trade. An image compressed hard at 4,000 pixels looks worse than the same image resized to 800 pixels and compressed gently.

Format choice matters more at small sizes

JPG is efficient for photographs but creates artefacts when quality is pushed low, usually as banding in smooth areas like skies and skin. WebP and AVIF hold up better at the same byte count because their encoders are more efficient, which is exactly the situation a 150KB budget creates. PNG avoids artefacts entirely for flat graphics but is a poor choice for a photograph, where it will be far too large.

• Photograph: WebP or AVIF gives the best quality at this budget, provided the destination accepts them.
• Photograph, JPG required: use the highest quality that fits and check for banding.
• Logo, icon, or flat graphic: PNG or WebP lossless keeps edges clean.
• Screenshot: crop to the part that matters, then compress. Tiny illegible text cannot be fixed by quality settings.

Batch behaviour and honest limits

A batch uses one quality setting across every file, which is usually right for a consistent set such as one gallery, and occasionally wrong for a mixed folder. If the batch contains a mix of a flat graphic and a detailed photograph, a single setting will over-compress one and under-compress the other. In that case, process them in separate batches. And if a file is already under the target, it is passed through unchanged rather than degraded for no reason.

• One setting across a consistent set produces a consistent result.
• Split a mixed folder into batches by content type.
• Files already within the limit are copied through unchanged.
• A file that cannot reach the target at acceptable quality is reported, not disguised as a success.
• Download the ZIP and check the byte counts before uploading.