Estimate call recording storage needed from calls, call length, retention, codec bitrate, tracks, and reserve margin in MB, GB, or TB.
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Call Recording Storage Formula
Storage (MB) = (Calls × Seconds_per_call × Total_kbps) / 8000 × (1 + Reserve)
- Calls: total recorded calls over the retention window
- Seconds_per_call: average call length in seconds
- Total_kbps: codec bitrate × number of tracks (1 mixed or 2 separate)
- Reserve: safety margin as a decimal (e.g. 0.10 for 10%)
Total calls depend on the input mode:
Calls/day mode: Calls = CallsPerDay × RetentionDays Agent mode: Calls = Agents × CallsPerAgent × Workdays/7 × RetentionDays Total mode: Calls = TotalRecordedCalls
Division by 8,000 converts kilobits per second × seconds into megabytes (1 byte = 8 bits, 1 MB ≈ 1,000 KB). Months are treated as 30.4375 days and years as 365 days. Bitrates assume constant-bitrate audio, so variable-bitrate codecs like Opus may come in slightly smaller in practice.
Bitrate and File Size Reference
Use this to sanity-check the codec choice against the file sizes you expect to land in storage.
| Codec / format | Bitrate | 6-min call (mono) | Common use |
|---|---|---|---|
| G.729 | 8 kbps | ~0.36 MB | Bandwidth-limited VoIP |
| GSM / AMR | 13 kbps | ~0.59 MB | Mobile, legacy archives |
| Opus voice | 24 kbps | ~1.08 MB | Modern WebRTC recording |
| MP3 low | 32 kbps | ~1.44 MB | Compressed archives |
| G.711 / μ-law | 64 kbps | ~2.88 MB | Standard PBX recording |
| WAV PCM 8 kHz 16-bit | 128 kbps | ~5.76 MB | Uncompressed quality control |
Two-track stereo recordings double these sizes. Add metadata, transcripts, or QA tags and you typically add another 1 to 5 percent on top.
Retention Periods by Industry
Retention is the biggest lever on total storage. Common targets:
| Sector | Typical retention | Driver |
|---|---|---|
| General sales / support | 30 to 90 days | QA and dispute review |
| PCI-DSS card payments | As short as possible; CVV not stored | Card data scope |
| Healthcare (HIPAA) | 6 years | US federal rule |
| Financial services (MiFID II) | 5 to 7 years | EU regulation |
| Debt collection (US) | Often 3+ years | FDCPA disputes |
Worked Example
A 35-agent contact center, 28 calls per agent per day, 5 workdays per week, 6-minute average length, G.711 mono at 64 kbps, 180-day retention, 10% reserve.
- Calendar-day calls: 35 × 28 × 5 / 7 = 700
- Total calls over 180 days: 700 × 180 = 126,000
- Seconds per call: 360
- Raw storage: 126,000 × 360 × 64 / 8,000 = 362,880 MB ≈ 363 GB
- With 10% reserve: about 399 GB
Switch the codec to Opus at 24 kbps and the same workload drops to roughly 150 GB recommended. Add a second track for separated agent and customer audio and the figures double.
FAQ
Should I size for raw or recommended storage? Provision the recommended figure. The reserve absorbs longer-than-average calls, retention overlap during deletion windows, and metadata overhead.
Do I need two tracks? Only if your QA, transcription, or speech analytics tools require separated channels. Mixed mono cuts storage in half.
Why does my actual usage differ? Variable-bitrate codecs, silence suppression, hold music, and post-call wrap recordings all change the real footprint. Recheck after 30 days of production data and adjust the bitrate or reserve.
What about backups? The result covers primary storage only. Multiply by your backup copy count and snapshot retention to size the full footprint.
