How to reduce audio file size for email or WhatsApp
Why recordings are so big, how small they can get without losing clear speech, and how to compress one in your browser in under a minute.
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In short
- Gmail sends attachments up to 25 MB in total, and Outlook around 20 MB. Bigger files are offered as a cloud link instead.
- Speech doesn't need much space. An hour of clear voice fits in about 15 to 22 MB as a mono MP3.
- Zipping barely helps. MP3 and M4A are already compressed.
- The free audio compressor shrinks a recording in your browser, without uploading it.
A recording that won't attach to an email is usually far bigger than it needs to be. This guide explains what decides audio file size, how small a voice recording can go and still sound clear, and how to compress one in a minute with the free audio compressor.
Why your recording is so big
Audio file size depends on three things: how long the recording is, the format, and the bitrate, which is how much data is stored for each second.
- WAV files aren't compressed. A stereo, CD-quality WAV uses about 635 MB an hour.
- MP3 and M4A are compressed. Music is usually 128 to 320 kbps; speech sounds clear at much less.
- Stereo stores two channels. A voice recording made with one microphone loses nothing as mono.
The sum is simple: kbps × 0.45 gives MB per hour. So 32 kbps is about 14 MB an hour, and 128 kbps about 58 MB.
| Format | About MB per hour | Good for |
|---|---|---|
| WAV, stereo, CD quality | 635 | Editing, archiving |
| MP3, 320 kbps | 144 | Music, best quality |
| MP3, 128 kbps | 58 | Music, everyday listening |
| MP3, 48 kbps mono | 22 | Clear speech |
| MP3, 32 kbps mono | 14 | Speech, smallest file |
Size limits you'll run into
- Gmail: 25 MB for all attachments together. Bigger files are offered as a Google Drive link.
- Outlook: around 20 MB, depending on the account.
- WhatsApp: large audio files are slow to send and can use a lot of mobile data. A small MP3 sends in seconds.
- Upload forms: many websites cap files at 10 or 20 MB.
Upload it as it is, up to 1 GB, and read the first part of the transcript free.
Upload a recordingReduce audio file size in your browser
- Open the free audio compressor.
- Choose the recording: MP3, WAV, M4A or the sound from a video, up to 200 MB and an hour long.
- Pick how small it should be:
- Smallest (voice, mono, 32 kbps): about 14 MB an hour.
- Voice (clear speech, mono, 48 kbps): about 22 MB an hour.
- Music (stereo, 96 kbps): about 43 MB an hour.
- Press Compress and download the MP3.
The file is compressed by your browser, on your device. Nothing is uploaded.
Tip
For speech, choose Voice. It keeps every word clear, and it's also what transcription works best with. Save Music for recordings where the music matters.
Which format to send
MP3 plays on every phone, computer and car stereo, so it's the safest choice when you don't know what the other person uses. M4A gives a slightly smaller audio file size at the same quality and plays on iPhones and Macs, but some older Windows apps can't open it. WAV is best kept for editing.
Whatever you send, keep the original recording until you're sure the compressed copy sounds right.
Why zipping doesn't work
A ZIP file shrinks text and documents well, but MP3 and M4A are already compressed, so zipping them saves almost nothing. Zipping a WAV saves a little more, but converting it to MP3 saves far more. To reduce audio file size, change the bitrate, not the container.
When to split instead
If even the smallest setting is too big for where you're sending it, or the recording is longer than an hour, split it into parts. The free audio splitter cuts recordings up to an hour into as many as 20 parts. See how to split audio into parts for longer files.
Other ways to send a big recording
- A cloud link. Upload the file to Google Drive, OneDrive or Dropbox and send the link. Nothing is compressed, so the quality stays the same.
- Trim it. If only part matters, cut the rest with the free audio cutter.
- Send the transcript. If the person needs what was said rather than how it sounded, a Word file of the transcript is a few hundred KB.
Compressing on a phone
The compressor runs in the phone's browser too. On iPhone, choose the file from the Files app or Voice Memos (share it to Files first). On Android, choose it from your Files app. Long recordings take longer on a phone than on a computer, so keep the screen on until it finishes.
What it costs
The audio compressor is free. Transcription is paid per file, after a free preview.
Prices today
| Option | Price | Good for |
|---|---|---|
| Preview | Free | Half the recording, up to 5 minutes. No account. |
| Pay per file | 10¢ a minute, $3 minimum per order | One longer file. Files uploaded together share one minimum. |
| Credit pack | $9 for 90 min · $19 for 240 min · $49 for 12 h | Lots of files. Credits never expire. |
The exact price is shown before you pay. See all prices
Questions
Does compressing audio lower the quality?
A little, but speech stays clear at the Voice setting. You'd notice the difference on music played through good speakers, not on a conversation.
What's the smallest audio file size for a voice recording?
About 14 MB an hour, as a 32 kbps mono MP3. That's small enough to email an hour-long recording.
Why is my WAV file so big?
WAV stores sound without compression, so its audio file size grows by about 10 MB every minute at CD quality. Converting it to MP3 usually makes it 10 to 45 times smaller.
Is my recording uploaded when I compress it?
No. The free compressor runs in your browser, and the file never leaves your device.
Can I compress a video's audio?
Yes. Choose the video, and the compressor saves its sound as a small MP3.
Free compressor in your browser, or a free transcript preview of the original.
Compress audioWritten with AI help.
Reviewed by Mubashar Rafique on 12 Oct 2026.