Compress Image to 20KB – Free Online, No Sign-Up

Twenty kilobytes is a very tight limit, and it usually appears in exactly one place: the signature box on an exam or application form. You scan your signature, the file comes out at 150KB or more, and the form refuses it. This free tool shrinks your image to under 20KB in your browser, with no sign-up and nothing to install.

Upload the image, click “Compress to 20KB”, and download the result. It is built for the small, simple images that a 20KB limit is designed for — signatures, passport-style photos and small scans.

How to compress an image to 20KB

Upload your image file, usually a scanned signature or a small photo.
Check the current file size shown on the page.
Click “Compress to 20KB”.
Download the result and confirm it is under 20KB before uploading it to your form.

A worked example

Imagine you are filling in an exam registration form that asks for a signature image under 20KB. You sign on white paper, photograph it with your phone, and the file is 180KB. That is nine times the limit, so the form rejects it. You upload the photo here and compress it to 20KB. The tool reduces the data until the file fits, and you download a version of about 18–19KB. Uploaded to the form, it passes the size check. Because a signature is mostly white space with a few dark lines, it compresses far better than a full-colour photo — simple images are exactly what this limit is made for.

Where a 20KB limit shows up

Exam registrations: many test and entrance-exam portals cap the signature upload at 20KB.
Government and job forms: signature and thumb-impression uploads often carry a 10–20KB limit.
University applications: some admission portals ask for a signature file under 20KB alongside a larger photograph.
Small profile icons: older systems and ID-card software sometimes limit small images to 20KB.

Tips for getting under 20KB

Because 20KB is so small, preparation matters more than with larger limits. Crop your scan tightly so no empty border wastes data, and use a clean white background — shadows and coloured paper add data that fights compression. A signature photographed in good light on plain paper will shrink far more easily than one on lined notebook paper. If the file still will not fit, crop closer or re-scan at a lower resolution, then compress again. Colour is also expensive in data terms: a black-and-white style scan of a signature compresses better than a full-colour photo of the same signature.

Honest limitations

20KB is extremely small, so detailed colour photos will lose visible quality. This limit is realistic only for simple images like signatures.
Compression cannot be undone, so keep your original scan and submit only the compressed copy.
Very small text in a scanned document may become unreadable at this size. Check the result before submitting.
If a portal also requires exact pixel dimensions for the signature, resize to those dimensions first, then compress.

Compress image to 20KB – frequently asked questions

Is this compressor free?

Yes. It is free, with no account, no sign-up and no watermark on your image.

Why does my photo not shrink to 20KB but my signature does?

A photo contains far more colour and detail than a signature, so it needs more data. Simple, high-contrast images compress much further than busy photographs.

Do I need to install anything?

No. The tool runs in your browser on a phone, tablet or computer.

What if the result is still over 20KB?

Crop tighter, use a plainer background, or re-scan at a lower resolution, then compress again.

Related tools: compress image to 50KB, compress image to 100KB and compress image to 200KB for larger upload limits.

Embed this tool on your website — free

Copy the code below to add this working tool to your own page. A small credit link stays with it — that’s all we ask.

<iframe srcdoc="&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
    &lt;meta charset=&quot;UTF-8&quot;&gt;
    &lt;meta name=&quot;viewport&quot; content=&quot;width=device-width, initial-scale=1.0&quot;&gt;
    &lt;title&gt;Compress Image to 20KB&lt;/title&gt;
    &lt;style&gt;
        body {
            font-family: Arial, sans-serif;
            padding: 20px;
            background-color: #f4f4f9;
        }

        h2 {
            color: #333;
        }

        .container {
            max-width: 600px;
            margin: 0 auto;
            background-color: white;
            padding: 20px;
            border-radius: 8px;
            box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.1);
        }

        input[type=&quot;file&quot;],
        button {
            width: 100%;
            padding: 10px;
            margin: 10px 0;
            border: 1px solid #ccc;
            border-radius: 4px;
        }

        #outputImage {
            margin-top: 20px;
            max-width: 100%;
            height: auto;
            display: block;
            margin-bottom: 20px;
        }

        #downloadLink {
            text-decoration: none;
            background-color: #008CBA;
            color: white;
            padding: 10px 20px;
            border-radius: 4px;
        }

        #downloadLink:hover {
            background-color: #007B9E;
        }

        #fileInfo {
            margin-top: 10px;
            color: #444;
        }
    &lt;/style&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;div class=&quot;container&quot;&gt;
    &lt;h2&gt;Compress Image to 20KB&lt;/h2&gt;
    &lt;input type=&quot;file&quot; id=&quot;imageInput&quot; accept=&quot;image/*&quot; onchange=&quot;loadImage(event)&quot;&gt;
    &lt;p id=&quot;fileInfo&quot;&gt;Current File Size: Not Available&lt;/p&gt;
    &lt;button onclick=&quot;compressToTargetSize(20)&quot;&gt;Compress to 20KB&lt;/button&gt;
    &lt;p id=&quot;progress&quot;&gt;&lt;/p&gt;
    &lt;br&gt;
    &lt;canvas id=&quot;canvas&quot; style=&quot;display:none;&quot;&gt;&lt;/canvas&gt;
    &lt;img decoding=&quot;async&quot; id=&quot;outputImage&quot; src=&quot;#&quot; alt=&quot;Output Image&quot; style=&quot;display:none;&quot;&gt;
    &lt;a id=&quot;downloadLink&quot; href=&quot;#&quot; download=&quot;compressed-image-20kb.jpg&quot; style=&quot;display:none;&quot;&gt;Download Compressed Image&lt;/a&gt;
&lt;/div&gt;

&lt;script&gt;
    let uploadedImage = null;

    // Load image and calculate file size
    function loadImage(event) {
        const file = event.target.files[0];
        if (file &amp;&amp; file.type.startsWith('image/')) {
            const reader = new FileReader();
            reader.onload = function(e) {
                uploadedImage = new Image();
                uploadedImage.onload = function() {
                    document.getElementById('outputImage').src = e.target.result;
                    document.getElementById('outputImage').style.display = 'block';
                }
                uploadedImage.src = e.target.result;

                const fileSizeKB = (file.size / 1024).toFixed(2);
                document.getElementById('fileInfo').textContent = `Current File Size: ${fileSizeKB} KB`;
            };
            reader.readAsDataURL(file);
        }
    }

    // Compress image to target size
    async function compressToTargetSize(targetSizeKB) {
        if (!uploadedImage) {
            alert('Please upload an image first!');
            return;
        }

        const canvas = document.getElementById('canvas');
        const ctx = canvas.getContext('2d');
        canvas.width = uploadedImage.width;
        canvas.height = uploadedImage.height;
        ctx.drawImage(uploadedImage, 0, 0, canvas.width, canvas.height);

        let quality = 0.9;
        const maxAttempts = 15;
        let attempt = 0;

        while (attempt &lt; maxAttempts) {
            const blob = await canvasToBlob(canvas, quality);
            const imageSizeKB = blob.size / 1024;

            if (imageSizeKB &lt;= targetSizeKB) {
                document.getElementById('progress').textContent = `Success! Final size: ${Math.round(imageSizeKB)} KB`;
                saveCompressedImage(blob);
                return;
            }

            quality -= 0.05;
            attempt++;
            document.getElementById('progress').textContent = `Attempt ${attempt}: ${Math.round(imageSizeKB)} KB (Target: ${targetSizeKB} KB)`;
        }

        alert('Could not achieve target size without significant quality loss.');
        saveCompressedImage(blob);
    }

    // Convert canvas to Blob
    function canvasToBlob(canvas, quality) {
        return new Promise((resolve) =&gt; {
            canvas.toBlob((blob) =&gt; resolve(blob), 'image/jpeg', quality);
        });
    }

    // Save compressed image
    function saveCompressedImage(blob) {
        const downloadLink = document.getElementById('downloadLink');
        downloadLink.href = URL.createObjectURL(blob);
        downloadLink.style.display = 'inline-block';
    }
&lt;/script&gt;

&lt;style&gt;html,body{height:auto!important;min-height:0!important;max-height:none!important}&lt;/style&gt;&lt;script&gt;(function(){function wpcPost(){try{parent.postMessage({wpcId:58,wpcH:document.body.scrollHeight},'*');}catch(e){}}window.addEventListener('load',wpcPost);try{new MutationObserver(wpcPost).observe(document.body,{childList:true,subtree:true,attributes:true});}catch(e){}window.addEventListener('resize',wpcPost);setInterval(wpcPost,600);})();&lt;/script&gt;&lt;/body&gt;
&lt;/html&gt;
" id="wpc-frame-58" class="wpc-embed-frame" style="width:100%;border:0;display:block;overflow:hidden;" scrolling="no"></iframe>
<p><a href="https://ilmhunt.com/online-compress-image-to-20kb/" target="_blank" rel="noopener">Online Compress Image to 20KB</a> by <a href="https://ilmhunt.com/" target="_blank" rel="noopener">IlmHunt</a> — free online tools</p>