PureTools
Compress MP3 and Audio Files Directly in Your Browser
Reduce audio file size privately in your browser. Choose a platform preset for WhatsApp or Discord, set a custom target, or pick a bitrate directly. Supports MP3, M4A, WAV, OGG and FLAC. No upload, no watermark, 100% private.
Drop your audio file here
or · up to 200 MB
Your file's duration is detected automatically. The bitrate is calculated to fit within the target size.
Enter a value between 1 and 200 MB. The compressor sets the bitrate automatically based on your audio's duration.
Quality mode does not guarantee a specific file size, it sets the bitrate directly.
Preparing…
How to use the MP3 Compressor
This tool reduces the file size of any audio file directly in your browser, no account, no server upload, no watermark. Choose a platform preset to hit a size limit automatically, enter a custom target size, or pick a bitrate directly for full quality control. An optional time range lets you compress only the part you need. The tool works on desktop and mobile and continues to function offline once loaded for the first time.
- Select your audio file, drag and drop a file onto the drop zone, or click Browse. MP3, M4A, WAV, OGG and FLAC are all supported, up to 200 MB. Your file's duration is detected automatically and shown in the file card.
- Choose a compression mode, Presets targets a platform's file size limit automatically, Custom size lets you type any target in MB, and Quality gives you direct control over the audio bitrate.
- Select your preset or set your target, in Presets mode, click WhatsApp (16 MB), Discord (25 MB) or Email (10 MB). In Custom size mode, enter your target in MB. In Quality mode, select a bitrate from 64 to 320 kbps.
- Set a time range (optional), enter a start and end time in HH:MM:SS format to compress only part of the audio. Leave both fields blank to compress the full file.
- Set the output filename, the field is pre-filled with the source file's name. Change it as needed; the
.mp3extension is added automatically. - Click Compress and download, the result card shows the original size, the compressed size, and the percentage saved. Click Download MP3 to save the file. No watermark is added.
How audio duration affects compression quality
When you use Presets or Custom size mode, the tool divides the target file size by the audio duration to calculate the highest bitrate that fits. A 3-minute file compressed to 16 MB can use about 711 kbps, far more than needed, so the bitrate is capped at 320 kbps and the file may be smaller than the limit. A 60-minute recording compressed to 16 MB gets only about 35 kbps, which degrades audio significantly. In that case, either trim the recording first using the Video to MP3 tool to extract only the section you need, or use Quality mode to set a specific bitrate instead of targeting a size.
Choosing between Presets, Custom size and Quality
Use Presets when the destination matters, WhatsApp, Discord or email, and you want the output to fit automatically without doing any math. Use Custom size when you have a precise limit in mind that is not covered by the presets, such as a cloud storage quota or a podcast host's file size cap. Use Quality when the final file size is not the primary concern and you want to control the listening experience directly: 128 kbps is the general-purpose standard, 192 kbps preserves music fidelity, and 64 kbps is suitable for speech-only content like voice memos and dictation.
Frequently asked questions
Is my audio file uploaded to a server?
No. Your audio file never leaves your device. The entire compression runs inside your browser without any server involvement. PureTools has no server infrastructure to receive files. You can disconnect from the internet after the page loads and the tool continues working. Your file exists only in your browser's memory and is discarded when you close the tab. Your data is never used to train AI models or improve machine learning systems.
What audio formats are supported?
The tool accepts MP3, M4A (AAC in an MP4 container, common on iPhone and iPad), WAV (uncompressed audio), OGG (open-source format) and FLAC (lossless audio). These cover the most widely used audio file types from smartphones, cameras, recording software and music downloads. The output is always an MP3 file for maximum compatibility across all devices and players. No watermark is added to any output.
How do platform presets work?
Each preset targets the maximum audio file size allowed by the corresponding platform. WhatsApp caps audio messages at 16 MB, Discord free accounts allow 25 MB, and most email providers accept attachments up to 10 MB. When you select a preset, the tool detects your audio file's duration and automatically calculates the highest bitrate that will keep the output within the target size. Longer files get a lower bitrate; shorter files can afford a higher bitrate, the calculation runs every time.
What is the difference between Presets, Custom size and Quality modes?
Presets mode targets a platform's size limit, the bitrate is calculated automatically from your file's duration so the result always fits. Custom size mode works the same way but with a size you type yourself, useful for email limits or storage quotas not covered by the presets. Quality mode ignores file size and lets you pick a bitrate directly: 64 kbps for speech, 96 kbps for voice and podcasts, 128 kbps for general use, 192 kbps for music, and 320 kbps for the highest fidelity. No watermark is added in any mode.
Will the output always match the target file size exactly?
The tool calculates the bitrate that should produce a file at or near your target, but the actual output size may differ slightly. Audio encoding is not perfectly linear, silence, transients and stereo width all affect how many bits each second actually uses. In practice, the result is typically within 5–15% of the target. If precision matters, try the Custom size mode with a slightly lower target than your limit, then check the result shown in the download card. If the file is still too large, compress again at a lower target.
Does compressing an MP3 reduce audio quality?
Yes, reducing the bitrate always discards some audio data. The effect depends on the source and the target bitrate. For voice recordings and podcasts, 64–96 kbps is typically indistinguishable from higher rates. For music, most listeners notice quality loss below 128 kbps. If your source is already a highly compressed MP3 at a low bitrate, compressing again will add more artifacts. In that case, Quality mode at 128 kbps will reduce the file size with minimal additional degradation. No watermark is ever added regardless of the quality setting chosen.
Is there a file size limit for the input?
Yes. The maximum input size is 200 MB per file. This limit protects your device's memory, the file is loaded into your browser's RAM for processing. Most audio files are well under this limit: a 3-minute MP3 at 320 kbps is roughly 7 MB, and a 60-minute podcast at 128 kbps is about 55 MB. If you have a very long recording, use the time range fields to compress only the section you need instead of processing the full file.
Does the tool work offline?
Yes, after your first visit. PureTools saves the tool locally on your device so it can be used later without an internet connection. The audio processing engine (~30 MB) is downloaded once on first use and then stored in your browser cache. On all subsequent visits, including offline, the tool loads from your local cache and the compression runs entirely without a network connection. For the most reliable offline use, open the merger once while online, then keep the browser cache intact before using it without a connection.
Is my data erased when I close the tab?
Yes, completely. Your audio file is held only in your browser's memory while the tab is open. Your preferences, selected mode, preset, custom size, bitrate and output filename, are saved for the current session only and cleared automatically when you close the tab. No file content, no audio data and no personal information is written to permanent storage or transmitted anywhere. Closing the tab erases everything instantly.