How To Compress PDF to a Chosen Size Online

Need to compress a PDF to meet a strict upload limit? While you can’t type in an exact target size, you can get very close quickly with the right compression settings and a few practical workarounds.

Oversized PDFs tend to fail at the worst moment. A form rejects your upload, an email won’t send, or a portal caps attachments at 1 MB and your PDF comes in just over the limit.

In this guide, we’ll show you how to compress a PDF to a chosen size using Smallpdf, plus what to do when standard compression isn’t enough for tight limits like 500 KB or 300 KB.

Use this table to choose the right approach first, then refine if needed.

Tip: If you only need a smaller file size, start with Basic. If you must hit a tight limit, start with Strong.

When people want to compress a PDF to a specific size, they usually mean:

• Get under a limit (like under 1 MB)

• Get as close as possible (like around 500 KB)

Most online tools, including Smallpdf, don’t let you enter an exact size like ‘make it 500 KB.’ PDF content varies too much. Instead, the tools optimize your file and show the final size, so you can adjust with extra steps if you’re still over the limit.

Smallpdf’s Compress PDF is the fastest way to shrink a PDF while keeping it readable.

Step 1: Open Compress PDF

Open Compress PDF in your browser.

You can upload from:

• Your device

• Google Drive

• Dropbox

• OneDrive

Step 2: Upload your PDF

Drag and drop your file into the upload area, or click “Choose Files.”

Step 3: Choose Basic or Strong compression

You’ll see two options:

• Basic compression: Great for everyday shrinking and usually keeps quality high.

• Strong compression: Pushes harder, especially on images. This often helps when you need to get under 1 MB, 500 KB, or 300 KB.

Step 4: Download and verify the file size

Download your compressed PDF, then check the size:

• Windows: Right-click “File” > “Properties”

• Mac: Right-click “File” > “Get Info”

If you’re still above the limit, use the tactics in the next section.

Use Basic Compression When:

• Your PDF is slightly too large.

• You want the cleanest look for images and charts.

• You are compressing a mostly text PDF.

Use Strong Compression When:

• You need a tight target like 1 MB, 500 KB, or 300 KB.

• Your PDF has photos, scans, or large images.

• Your file includes a lot of embedded objects.

Quick rule: If the portal limit is strict, start with Strong. If quality matters most, try Basic first.

If your file won’t shrink enough, it usually contains one or more of these:

• High-resolution images or scanned pages

• Large color photos (especially full-page scans)

• Embedded fonts and heavy formatting

• Layers, transparency, or complex graphics

• Extra pages you don’t need

• Hidden metadata or form data

Compression reduces size by optimizing how images and other elements are stored. Strong compression typically reduces image resolution more aggressively, which is why it often hits stricter limits.

When compression gets you close but not under the limit, combine tactics. These give you the best chance of meeting strict upload rules.

1. Split the PDF, Then Compress Each Part

If a portal lets you upload multiple files, splitting works well.

• Use Split PDF to break the file into sections.

• Compress each smaller PDF.

• Upload each part separately, or merge later if needed.

2. Remove Pages You Don’t Need

If your PDF includes extra pages, removing them is one of the fastest size wins.

• Use Delete PDF Pages to remove blank pages, duplicates, or unnecessary appendices.

• Compress again after removing pages.

3. Crop Oversized Margins

Large margins can waste space in scanned files.

• Use Crop PDF to trim white borders.

• Then compress the cropped file.

4. Convert Color Scans to Grayscale

Color scans are often massive compared to grayscale scans.

If color is not required:

• Convert your source scan to grayscale before creating the PDF, if you can.

• If you can’t, try Strong compression and consider splitting.

5. If It’s a Scan, Re-Scan Smarter

If you control the scan, this is the best fix.

• Scan at 200–300 DPI for standard forms.

• Use grayscale for text-heavy documents.

• Avoid photo scan modes unless you need them.

6. Last Resort: Image-Based PDF Rebuild

If you must hit an extreme limit, you can rebuild the PDF as images.

• Convert PDF pages to JPG.

• Recombine them into a PDF.

• Compress again.

This often shrinks files heavily, but you may lose selectable text.

If you can’t use an online compressor, here are the built-in options.

How to compress a PDF on Mac using Preview

• Open the PDF in Preview.

• Go to “File” > “Export.”

• Choose “Quartz Filter” > “Reduce File Size.”

• Save with a new name.

This is quick, but it can reduce the quality heavily on image scans.

Windows workaround: Print to PDF

Windows does not include a real compressor, but you can try this:

• Open the PDF in Microsoft Edge.

• Press “Ctrl + P.”

• Select “Microsoft Print to PDF.”

• Save a new file.

This can reduce size sometimes, but results vary.

If Strong compression still doesn’t get you under the limit, the PDF is usually image-heavy or already optimized.

1. If Strong Compression Barely Reduces Size

Your file may be:

• Mostly vector graphics

• Already compressed

• Built from optimized fonts and minimal images

Try a different tactic:

• Remove pages.

• Split the file.

• Re-export from the source file with lower image quality.

2. If the PDF Is a Scanned Document

Scans are often the hardest to shrink.

• Re-scan with lower DPI if possible.

• Use Strong compression.

• Split into sections if the portal accepts multiple uploads.

3. If You Need To Keep Quality High

If quality matters more than size, aim for under the limit but not ultra-small.

• Use Basic compression first.

• Only use Strong if needed.

If you’re trying to get under a strict limit, you want predictable results, strong upload support, and simple steps.

Smallpdf works well for strict limits because you can compress, then immediately apply a second step like splitting, deleting pages, or cropping, without restarting your workflow.