Enter mailbox count, retention days, average message length, and recording codec — get GB needed, recommended disk spec, backup window, and 3-year growth projection.
Unity VM sizing is often guessed based on user count alone, which underestimates storage for anyone with 30+ day retention or 100-agent call centers. This calculator models storage as (mailboxes × messages-per-day × retention × avg-length × codec-bitrate) + greetings + overhead, produces a 3-year projection including growth, and recommends the Cisco Unity Connection VM OVA tier that fits.
Fill in the sizing inputs, click Calculate storage.
Storage grows with mailbox count + retention. Size for year 3.
Cisco ships Unity OVAs in discrete sizes. Pick the one above your peak.
Plan the DRS backup window around peak storage, not current.
The formula for voicemail storage is deceptive because it looks simple. 500 mailboxes × 30 days × 1.5 messages/day × 45 seconds × 8 KB/s = ~8 GB. Sounds fine. Now make it a call center: 200 agent mailboxes receive 15 messages per day each during a campaign. That's 10× the message volume in 40% of the users. Suddenly you need 40 GB just for messages, plus growth, plus transcription overhead, plus greeting storage. The call-center pattern is the single biggest Unity storage surprise.
Codec choice used to matter a lot (G.729a is 8× smaller than G.711), but most modern deployments use G.711 or G.722 for quality reasons — disk is cheap, voice quality isn't. Don't store in G.729 unless you have a hard space constraint; the transcoding cost at every greeting playback isn't worth the savings. G.722 gives wideband quality at the same storage cost as G.711.
Transcription adds 15–25% overhead — Unity stores both the WAV and the text. If you've enabled transcription cluster-wide (not just for executives), plan the overhead. If you're running low on space, transcription is usually the first thing to turn off per-COS.
± 20% vs. production. Biggest variable is actual messages-per-day — highly skewed by call centers + shared mailboxes.
200, 1K, 5K, 10K, 20K user tiers. Disk sizes: 200 GB, 300 GB, 500 GB, 1 TB, 2 TB respectively (approximate).
No — Unity keeps a lightweight copy locally while the primary lives on Exchange. Plan ~30% of pure-Unity size if SIB is enabled.
DRS full backup = ~1.5× live storage. Plan 2× for backup retention (one full + one incremental cycle).
500 mailboxes, 30-day retention, 1.5 msg/day, 45s avg, G.722, 5% growth.
2,000 mailboxes, 90-day HIPAA retention, 2 msg/day, 60s avg, G.711, 10% growth.
200 agent mailboxes, 30-day retention, 12 msg/day, 90s avg, G.722, 5% growth.
Our Health Assessment audits Unity utilization + projects 3-year growth — delivered as a board-ready spec + spend plan.