How the calculation works
Each camera produces a roughly constant data stream determined by its resolution. The calculation is bitrate × hours × days × cameras, adjusted for the compression method and the recording mode. The figures we use are realistic averages taken from actual installations:
- 2MP ≈ 2 Mbps
- 4MP ≈ 4 Mbps
- 5MP ≈ 5 Mbps
- 8MP (4K) ≈ 8 Mbps
H.265 compression saves roughly 40% over H.264 at the same quality, and motion-triggered recording typically saves 60–70% depending on how busy the scene is. Those two settings move the result more than anything else on this page.
What the calculator cannot know
The figure is an estimate and lands close to reality, but some factors shift it. A busy scene — a street, a production line — produces more data than a still room, and poor lighting adds noise which increases file size. For that reason we always suggest adding 20% headroom to the result.
Why a surveillance-grade drive matters
Surveillance drives such as WD Purple are designed for continuous writing, 24 hours a day, all year. An ordinary desktop drive is designed for intermittent duty cycles and fails quickly under constant recording — it is the single most common complaint we hear from people who installed a system with a standard drive.
Need help choosing?
If the result is larger than you expected, there is usually a cheaper answer: reduce retention on the less important cameras, or use motion recording in quiet areas while keeping continuous recording at the entrances. Get in touch and we will work out the split with you.
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