How it works
The formula, without the black box.
TB = cameras × Mb/s × recorded seconds ÷ 8 ÷ 1,000,000
The division by 8 converts bits to bytes. Dividing by 1,000,000 converts megabytes to decimal terabytes. The visible overhead percentage is added after raw video volume.
Inputs that deserve a second look
- Camera count
- Cameras sharing the same average bitrate. Use the system planner for mixed groups.
- Average bitrate
- The mean main-stream rate in megabits per second. Variable bitrate can move substantially by scene.
- Recorded time
- Days × recording hours per day × recorded activity.
- Overhead
- A planning allowance for container, index, and filesystem use—not RAID protection or free-space reserve.
Common planning mistakes
- Using maximum network bitrate as a typical storage average without scenario testing.
- Assuming motion-only recording has one universal activity percentage.
- Confusing decimal drive TB with binary TiB reported by some software.
- Forgetting audio, metadata, pre-roll, analytics, or secondary streams when the recorder stores them.
Questions installers ask
How many TB do eight 4 Mb/s cameras need for 30 days?
At continuous recording, raw video is about 10.37 decimal TB. With 10% overhead the planning target is about 11.40 TB, before RAID and free-space reserve.
Is H.265 always half the storage of H.264?
No. The saving depends on the exact encoders, scene, quality target, frame rate, GOP, and motion. Compare measured or manufacturer-tested bitrates for the same quality goal.
Should I enter peak or average bitrate?
Use a realistic average for capacity, then check peak bitrate separately against network and recorder incoming-bandwidth limits.
Sources and boundaries
These links support the method or terminology. They do not turn a planning estimate into a site guarantee.
ONVIF Profile T overview ↗
Industry context for H.265, metadata, and streaming interoperability.
Seagate surveillance storage calculator ↗
Confirms the core planning variables used by a storage manufacturer.