VMS Storage

The formula

Exactly what the calculator computes, in the order it computes it. Highlighted terms are your inputs.

// Estimated bitrate, when not entered directly
bitrate(Mbps) = width × height × fps × bitsPerPixel ÷ 1,000,000

// bitsPerPixel by codec and scene complexity
  H.264   low 0.060   medium 0.100   high 0.180
  H.265   low 0.030   medium 0.050   high 0.090

// VBR averages below its ceiling; CBR does not
effective = bitrate × (VBR ? 0.85 : 1.00)

// Storage — decimal GB and TB, which is how drives are sold
GB/day    = effective × 86,400 × dutyCycle ÷ 8 ÷ 1,000
total TB  = GB/day × retentionDays × cameras ÷ 1,000
recommend = total TB × (1 + headroom)

// Binary conversion, which is what the OS will show you
TiB = TB × 10¹² ÷ 1024⁴

What it assumes

Each of these is a way the number can be wrong for your job. Read them before you buy hardware.

1. The bits-per-pixel model is an estimate, not a measurement. Real bitrate depends on the encoder, its rate-control tuning, GOP length, I-frame interval, noise floor, and how much the scene actually moves. If you can get the real bitrate from the camera or a bench test, enter it directly — the estimate can be off by a factor of two on an unusual scene.
2. Smart codecs are not modelled. Zipstream, H.264+/H.265+, Wisestream and similar can cut bitrate 30–70% on quiet scenes and almost nothing on busy ones. If you are relying on one, measure it rather than estimating.
3. Decimal TB throughout. 1 TB = 10¹² bytes, which is how drive manufacturers sell capacity. Your operating system reports TiB (1024⁴ bytes), about 9% smaller. Both figures are shown so you can size the array and still recognise the number the OS gives you.
4. Usable capacity is less than raw capacity. This calculates the video payload plus your stated headroom. It does not account for RAID parity, hot spares, or filesystem reserve. A RAID 6 array of ten 12 TB drives is 120 TB raw and about 96 TB usable before you have stored a single frame.
5. Motion duty cycle is your estimate, and people are consistently optimistic about it. Foliage, headlights, rain, insects at night, and HVAC-driven shadows all trigger recording. Measure it on site before you rely on it for a retention commitment.
6. The VBR factor of 0.85 is a planning convention, not a measured property of your system. It is applied and disclosed rather than hidden. If your VMS reports its own average, use manual bitrate entry instead.
7. Audio, metadata, and analytics streams are not included. Audio adds roughly 0.5–1.5 GB per camera per day at typical settings. Analytics metadata is usually small but is not zero.
8. No sustained-write check. Aggregate write bandwidth is shown so you can sanity-check it against the storage subsystem, but this calculator does not verify that your array can absorb it.