Calculate audio duration from file size & bitrate
💡 Why This Matters Whether you're planning a podcast episode, uploading music, or preparing a voice memo, knowing your file's duration helps with planning and ensures your content fits your intended slot.
Duration
MP3s at 128 kbps were the standard for decades because that's roughly the bitrate where most listeners stop noticing compression artifacts on typical earbuds — audiophiles can still hear the difference at higher rates.
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How It's Calculated: The formula is straightforward: Duration (seconds) = (File Size in MB × 8 × 1000) ÷ Bitrate (kbps). A 5MB file at 128 kbps yields approximately 312 seconds or about 5 minutes of audio.
Why Bitrate Matters: Higher bitrate means better quality but larger files. 128 kbps is standard for voice recordings, 192 kbps suits podcasts, 256 kbps is good for streaming quality, and 320 kbps approaches CD quality. Choose based on your use case—voice can get away with lower bitrates.
Common Use Cases: Podcasters need to calculate episode length before recording. Musicians preparing demos for submission need file durations within limits. Video creators calculating background music lengths. Voice memo transcriptions estimating turnaround time.
Using Your Results: Use the calculated duration to plan content slots. If a podcast accepts max 45 minutes and your calculation shows 52 minutes, you know to trim or reduce quality. For music submissions with time limits, verify compliance before uploading.
Limitations: This calculation assumes constant bitrate (CBR). Variable bitrate (VBR) files may slightly differ. Metadata, album art, and container overhead add minor size. Network streaming adds buffering time not reflected here.
Example: Say your file is 5 MB and encoded at 128 kbps. Plug those into the formula: (5 × 8 × 1000) ÷ 128 = 40000 ÷ 128 = 312.5 seconds, which is about 5:12 — a full song, not a short clip.
Not precisely — this calculation assumes constant bitrate (CBR). VBR files encode at a fluctuating rate, so the actual duration may differ slightly from the estimate.
Metadata, album art, and container overhead add a small amount of size that isn't audio data, which can throw off the estimate by a few seconds on smaller files.
192 kbps is a common sweet spot for podcasts — noticeably better than the 128 kbps voice-memo standard, without the file size of 256 or 320 kbps streaming/CD-quality rates.