A 4K camera at 25 fps in H.264 records ~14 Mbps — that’s ~86 GB a day per camera [5]. Multiply by 16 cameras and 30 days: ~13 TB minimum — no RAID overhead, no safety margin, no surprises.

CCTV storage sizing is four variables multiplied together: bitrate × hours × retention × cameras. Get one wrong and your recorder silently overwrites evidence before the retention window ends.

The actual numbers for H.264 at 25 fps: 2 MP ≈ 4 Mbps, 4 MP ≈ 6 Mbps, 8 MP (4K) ≈ 14 Mbps [5]. With H.265 (HEVC) those drop roughly in half. With smart codecs (H.265+, WiseStream II, Zipstream), ~75% less than H.264 [3]. That single decision is the difference between a 4 TB drive and a 12 TB drive for the same job.

How many days? EU retail converges on 30 days as the operational default (AEPD Spain, CNIL France, ICO UK); Italy is tighter: 24 hours standard, 7 days maximum [4]. Banks and ATMs: 90 days minimum under AML. For your site, start at 30 days and double it if your fraud window is longer.

Two details no calculator remembers:

  1. Multiply your observed average bitrate by 1.5x as a safety factor [1]. Real bitrate during peak motion runs 2-3x the average.
  2. RAID isn’t free. RAID 5 loses one drive; RAID 6 loses two. A 6×4 TB array in RAID 6 yields ~16 TB usable, not 24.

The storage design framework sits in IEC 62676-4:2025 Part 4 — Storage requirements [6]. It’s the reference any European audit will ask for.

Every time I review a deployment for tv4agent, the question that drives most of the storage budget isn’t “what camera?”. It’s “how many days, at what fps?”. That answer decides roughly 70% of storage cost.

P.D. Does your current footage actually last the 30 days without overwriting? If you don’t know, today’s a good day to check the bitrate configured on each camera — not the datasheet number, the live one.

📰 Source: MEPBase CCTV Storage Calculator + Storage Calculators (Hikvision H.265+) + CCTVplanner 2026 EU retention reference + IEC 62676-4:2025. Data accessed 2026-09-02.

Sources

[1] https://www.vodanetsystems.com/blog/post/axis-zipstream-storage-calculator-nvr-sizing-guide [3] https://storagecalculators.com/hikvision-storage-calculator [4] https://cctvplanner.io/blog/cctv-recording-retention-period-by-country [5] https://tools.mepbase.com/cctv-storage-calculator [6] https://webstore.iec.ch/en/publication/83425

Sources

[1] Vodanet Systems — Axis Zipstream Storage Calculator: NVR Sizing Guide — https://www.vodanetsystems.com/blog/post/axis-zipstream-storage-calculator-nvr-sizing-guide [2] MEPBase — CCTV Storage Calculator — https://tools.mepbase.com/cctv-storage-calculator [3] Storage Calculators — Hikvision Storage Calculator — https://storagecalculators.com/hikvision-storage-calculator [4] CCTVplanner — CCTV recording retention period by country (2026 EU + UK + US) — https://cctvplanner.io/blog/cctv-recording-retention-period-by-country [5] IEC 62676-4:2025 — Video surveillance systems for use in security applications, Part 4: Application guidelines — https://webstore.iec.ch/en/publication/83425