Compress an Image to a Target File Size

Set a KB budget — it binary-searches the best JPEG/WebP quality that lands under it, right in your browser.

About this tool

Some upload forms cap images at an exact file size — "photo must be under 200 KB", "200 x 200 and below 100 KB", "logo max 50 KB". Guessing a quality slider until you land under the limit is tedious. This tool does the search for you: give it a target size in kilobytes and it re-encodes your image at several quality levels, measures each result, and keeps the highest quality whose file is at or under your budget.

Everything runs locally in your browser with ffmpeg compiled to WebAssembly — the image is never uploaded to a server.

How it works

Choose an image (JPG, PNG, WebP, GIF, or BMP).
Enter your Target size (KB) — for example 200.
Pick the Output format: JPEG (widest compatibility) or WebP (usually smaller at the same quality).
Optionally set a Max width to shrink wide images first — helpful when a small target can't be met at full resolution.

The tool binary-searches the encoder quality between 5 and 95 (about seven attempts), then shows the achieved size and the quality it settled on, with a download link.

Worked example

Upload a 1.8 MB, 3000-px JPEG and set Target size to 100 KB with format JPEG. The search converges on roughly quality 47 and produces a file near 98 KB — under the 100 KB budget. The status line reads something like: Done — 98.2 KB at quality 47 (target 100 KB). If you also set Max width to 1200, the image is shrunk to 1200 px wide first, so the same 100 KB budget buys a higher quality.

Limits and edge cases

Output is JPEG or WebP only. Both have a quality knob to search. PNG is lossless (no quality knob), so it isn't offered as an output — pick JPEG or WebP instead.
Target is a ceiling, not an exact value. The result lands at or just under your target; it won't be padded up to match it exactly.
Very detailed photos may not reach an aggressive target at full resolution. When even the lowest quality is still too big, the tool returns the smallest version it can make and tells you — lower the Max width and try again.
Max input size is about 8 MB. Exotic inputs (HEIC, AVIF, TIFF, SVG) may not decode; convert them to JPG/PNG/WebP first.
1 MB = 1024 KB, so enter 1024 for a 1 MB budget.

FAQ

How do I compress an image to exactly 100 KB (or 50 KB, 20 KB)?

Enter the number in the Target size (KB) field and choose a format. The tool finds the best quality that fits at or under that size. It targets a ceiling, so a "100 KB" result is typically in the high-90s KB — under the limit, which is what upload forms check.

Why is the output only JPEG or WebP — can I keep it as PNG?

Hitting a target size needs a lossy quality knob to search against. JPEG and WebP have one; PNG is lossless and has no equivalent, so a "compress PNG to 50 KB" request can only be met by re-encoding to JPEG or WebP. Choose whichever format your destination accepts — WebP is usually the smaller of the two at the same visual quality.

What does "Max width" do, and when should I use it?

It caps the output width in pixels (height scales to match, and it only ever shrinks — a smaller image is left alone). Reach for it when a tight target can't be met at full resolution: a 4000-px photo squeezed under 50 KB looks blocky, but the same 50 KB spread over an 800-px image looks fine. Leave it at 0 to keep the original dimensions.

Is my image uploaded anywhere?

No. The compression runs entirely in your browser using ffmpeg compiled to WebAssembly. The image bytes never leave your device, so it works offline and keeps private photos private.

The result is a bit under my target — can I get closer to the exact size?

The search picks the highest quality that stays at or under your budget, so there's usually a small gap below the target (the next quality step up would exceed it). That gap is expected and safe for upload limits. If you need a larger file, raise the target or increase the Max width.

Developer & Automation Access

Run it from the terminal

Same engine as this page, headless — via the gizza CLI:

gizza tool image-resize-to-filesize 'url=https://example.com/input' 'target_kb=200' 'format=jpg' 'max_width=0'

New to the CLI? Get gizza →

Open it by URL

Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:

https://gizza.ai/tools/image-resize-to-filesize/?url=https://example.com/input&target_kb=200&format=jpg&max_width=0