File Compressor: Pick the Right Tool by File Type

Last reviewed 2026-05-08. Every tool linked from this page runs in your browser on your own device - no file is uploaded to any server.

Why "file compressor" is not a single tool

People searching for a "file compressor" arrive with five different inputs and five different goals. A folder of receipts heading into Gmail's 25 MB attachment limit. A stack of iPhone photos that need to open on a Windows desktop. A 4K video that has to fit a Slack DM. Twelve scanned PDFs the lawyer asked for as one file. A 200 MB design source going to a printer. The naive answer - "use a free file compressor" - hands all five users the same tool, and four of them get a worse outcome than if they had picked the right specialist. The decision tree below maps your input to the right tool in one click.

The reason there is no universal compressor is that the underlying compression math is different for each file type. ZIP-ing a folder of JPGs saves almost nothing (JPG is already compressed). Image compression does not help a folder structure. Video re-encoding cannot run on a 4 GB file in a browser tab. Converting HEIC to JPG is about device compatibility, not byte savings. The five tools listed here each beat a generic "file compressor" for their specific case - and they all run on your device with no upload to a server.

Decision table - what tool by what you have

If your input is a folder for email and you want a step-by-step rather than a tool tour, jump straight to how to compress a folder for email. If your input is one file rather than a folder, see how to compress a file online. If you already have a ZIP that came out too big, see how to make a zip file smaller.

Folder of mixed files: ZIP it

A "folder" - documents plus a few spreadsheets plus some photos plus a couple of PDFs - is the case ZIP was designed for. The Zip File tool bundles every file into one .zip archive, applies DEFLATE compression to the byte stream, and gives you a single download to attach or upload. The whole job runs locally in the browser using the JavaScript Streams API + Compression Streams API - no upload to any server, no signup. Size cut is 20-50% when the folder is text-heavy (documents, source code, CSV) and 1-3% when the folder is dominated by JPG / PNG / MP3 / MP4 because those formats are already internally compressed and the DEFLATE algorithm cannot squeeze them further.

If the .zip comes out larger than the upload limit anyway (most often when the folder is photo-heavy), the right move is not "compress harder" - it is "compress the photos first, then ZIP the folder". See how to compress zip file to smaller size for the photo-first workflow.

Loose photos: compress the images

If your input is a few JPG or PNG photos rather than a folder, image compression beats ZIP by a wide margin. The Compress Image tool re-encodes each JPG at a lower quality setting (typically quality 60-80) so the file becomes 30-70% smaller with no visible difference to the human eye in normal viewing conditions. The compression runs on the Canvas + FileReader APIs entirely in the browser - the original photo never leaves your device.

For PNGs that are actually photographs (i.e. screenshots of photos rather than diagrams or screenshots of UI), converting PNG to JPG before compression cuts the file 90% on top of any quality reduction. PNG is a lossless format intended for screenshots, line art, and graphics with transparency - using it for photos wastes most of the file size. For the comparison see JPG vs PNG for web. For the full visual quality vs size trade-off see how to choose a compression level.

iPhone HEIC photos: convert to JPG

HEIC is the default photo format on every iPhone since iOS 11. It is a strong format - typically half the size of the equivalent JPG - but it does not open on Windows desktops without a paid codec install, and it does not open at all on older Android phones, on most printers, on most CMS upload forms, and on many email clients. The HEIC to JPG converter turns each HEIC into a JPG that opens everywhere. The file size lands in the same range or slightly larger - this is a compatibility win, not a size cut. For the format trade-off see HEIC vs JPG vs WebP.

The conversion runs locally using libheif compiled to WASM and the Canvas API. Nothing uploads. If you have a phone full of HEIC photos and you need them all converted at once, see how to convert 100 HEIC photos to JPG.

Several images for one recipient: bundle into a PDF

When the input is several images all going to the same person - scanned receipts, contract pages, screenshots of an issue, photos of damage for an insurance claim - the recipient experience is much better with one PDF than with ten attachments. The Images to PDF tool stitches every image into a single multi-page PDF in the order you arrange them. Total file size lands within 0-20% of the sum of the inputs - the gain is that the recipient gets one tap to open everything in order rather than ten files in arbitrary order in their inbox.

The PDF is generated locally with PDFKit / pdf-lib in the browser. No upload. If the resulting PDF is itself too large for the upload limit, run the source images through Compress Image first.

Several PDFs for one recipient: merge them

When you already have several PDFs - say a contract plus a cover letter plus a few attachments - the right move is to merge them into one rather than attach each separately. The Compose PDF tool concatenates every input PDF into one ordered output. A typical 5-15% size cut comes from de-duplicating shared metadata and font subsets across the inputs. The merge runs in the browser using pdf-lib; the source PDFs do not upload.

One very large file: use a transfer link

When the input is a single large file - a 4K video, a RAW photo, a Photoshop / Illustrator / Figma design source, a database dump - browser-only compression is not the right answer. Video re-encoding hits memory limits in the browser tab around 1-2 GB. RAW photos are already minimum-size for their resolution. Design sources have file-format-specific assumptions you do not want to disturb. The right move is to host the file on a transfer service (Google Drive, Dropbox, WeTransfer, OneDrive) and send the recipient a link. The file stays full quality, the recipient downloads it on their schedule, and the link itself fits in any email or chat message.

Six kinds of compression, six different math

The reason no single tool does all five jobs is that "compression" means six fundamentally different algorithms. Understanding the math helps you pick the right one and helps you not be surprised when one of them fails on your input.

• Lossless container compression (ZIP, 7z, RAR). Bundles many files into one archive and compresses the byte stream with DEFLATE / LZMA / LZMA2. Reversible - the extracted files are bit-for-bit identical to the originals. Excellent on text, source code, and CSV (50-80% cut). Almost no effect on already-compressed media (JPG / MP4 / MP3 / PDF). The right choice when you need to preserve the exact files.
• Lossy image compression (JPEG quality, WebP). Discards visual information the human eye is least likely to notice and re-encodes the result. Drops a 5 MB JPG to 1 MB at quality 80 with no visible difference for most photos. Not reversible - once compressed at quality 60 you cannot recover the original. The right choice when the file is one image and the recipient does not care about pixel-perfect fidelity.
• Image format conversion (HEIC to JPG, PNG to JPG, TIFF to JPG). Changes the encoding format. The size change is a side-effect of moving from a less efficient format to a more efficient one. PNG to JPG cuts a 12 MB photograph to 1 MB; HEIC to JPG keeps the size similar but unlocks every Windows / Android device. The right choice when the file is the wrong format for the recipient.
• Lossy video compression (re-encode at lower bitrate). Re-encodes the video stream at a lower bits-per-second target. Cuts a 1 GB 4K MP4 to 200 MB at 1080p H.264 with acceptable quality. Browser tools handle short clips; long videos go through dedicated software like FFmpeg or HandBrake.
• Lossy audio compression (MP3 / AAC / OGG). Same idea as video but for sound. A 50 MB WAV becomes a 5 MB MP3 at 192 kbps. Browser ZIP does not help; the right move is format conversion in dedicated audio software.
• Hosting a transfer link. Not technically compression - the file stays the same size, but the recipient downloads it from a service instead of receiving an attachment. This is the only practical answer for files over ~25 MB, the upper bound for most email systems.

Privacy: why "browser-only" matters

Most "free file compressor" results upload your files to a server, run the compression in the cloud, and email you a download link. That is fine for cat photos. It is not fine for HR forms, medical records, contracts, source code, or anything subject to GDPR / HIPAA. The five tools linked from this page all run on your own device using browser-native APIs (the ZIP tool uses the JavaScript Streams + Compression Streams API; the image tools use Canvas + FileReader; HEIC conversion uses libheif compiled to WASM; PDF tools use pdf-lib). Nothing leaves your computer or phone. For the broader category see free online tools that work without uploading files.

Related deep-dives on this site

• What is a file compressor and which to use - the long-tail explainer that walks through every compression operation in detail.
• File Compressor vs ZIP: what to pick - tighter focus on the ZIP-vs-image-compression decision.
• File compressor online: ZIP a folder vs compress an image - workflow-first companion to the table above.
• When to compress vs convert an image - the image-only sub-decision in depth.

What to do next

Pick the row in the decision table above that matches what you have, click through to the matching tool, and run it. If your input does not fit any row - for example you have a single very large CSV or a folder full of WAV audio - the closest fits are usually Zip File for the CSV (text compresses extremely well) and a transfer link for the audio folder (browser-only audio compression is not in the toolkit). For everything else, the five tools listed here cover the five canonical "file compressor" intents end-to-end.