画像を100KBに圧縮する

Every online form, portal, and platform that asks for a photo comes with a file size ceiling, and 100KB is one of the most common ones. A typical phone or camera photo is measured in megabytes, far above that limit, so it must be shrunk before it can be uploaded at all. When a government portal, visa application, job board, university page, or content system rejects an oversized file, the fix is not a new picture but a smaller one. Most people hit these limits by surprise, right at the upload button, and a target-size compressor turns that frustrating rejection into a one-click fix. UnoIMG’s free Compress Image to 100KB tool exists for exactly this moment: it takes any image you upload and brings it down to meet the 100KB cap without you touching a quality slider or guessing at pixels.

The tool works by targeting the size you need instead of a fixed percentage. It opens your image in the browser, then runs a binary search across quality levels to find the highest setting that still fits under 100KB, which means you keep the sharpest picture the limit allows. If quality reduction alone cannot reach the target on a very large original, it gently reduces the resolution just enough to get there, so the result always lands at or below the cap. You watch the before and after size while you work, can switch the output between JPEG, WEBP, or lossless PNG, and never wait on a server, because every calculation happens locally on your device. Because the algorithm measures the real output after each pass, it does not rely on the rough estimates a simple quality slider would give, and it stops the moment the cap is met.

A 100KB limit is the single most common upload cap on the web, used by DS-160, USCIS, EU visa portals, and university applications; at document dimensions the output is visually indistinguishable from the source.

This is the web’s most quoted upload cap: DS-160 and USCIS visa forms, EU visa portals, and UCAS university applications all expect around 100KB. At document dimensions a JPEG looks identical to the original, so you meet the limit with no visible loss on screen.

Best of all, the whole process stays free and private. Your image is decoded, measured, and re-encoded inside the browser tab you are using, so it never travels to a server, never sits in a queue, and never gets stamped with a watermark. There is no account to create and no daily limit, so you can compress one urgent form photo or an entire folder of listing images whenever you need to. You stay in control of the format and the trade-off, and you can re-run with a different size in seconds if a portal asks for something else. That combination of exact targeting, real-time feedback, and zero-cost privacy is why UnoIMG fits naturally into any upload workflow, whether you are meeting a hard 100KB government limit or simply keeping your website fast.