How Much CCTV Storage Do You Really Need? Complete HDD Sizing Guide

One of the most common mistakes on a CCTV project is under-sizing the NVR storage. The system looks fine on day one, but two weeks in the oldest footage is already being overwritten — right when an incident from ten days ago needs to be reviewed. Getting storage right before installation costs nothing. Getting it wrong costs a second site visit, a new hard drive, and the footage you no longer have. This guide walks through exactly how CCTV storage is calculated and how to use our free CCTV HDD Storage Calculator to size any setup correctly in under a minute.

The storage formula: what actually drives HDD size

CCTV storage is a function of four things: how many cameras you have, how much data each camera generates per second (bitrate), how many hours per day they record, and how many days of footage you need to keep. Everything else — resolution, codec, frame rate, quality setting, and recording mode — feeds into that bitrate number. The core formula is:

• Total storage = (bitrate per camera in Mbps ÷ 8) × cameras × seconds recorded per day × retention days
• Add 10–20% overhead for filesystem metadata, NVR indexing, and safety margin
• Then map to the nearest standard HDD size (1TB, 2TB, 4TB, 6TB, 8TB, 10TB, 12TB, 14TB, 16TB)

Our CCTV Storage Calculator handles all of this automatically — including per-brand bitrate estimates, codec adjustments, and motion-detection activity percentages. But understanding the inputs helps you configure it accurately.

Resolution: the biggest single driver of storage

Resolution determines the base bitrate before codec compression. A 2MP (1080p Full HD) camera at medium quality with H.265 encoding runs around 2 Mbps. Scale that up to 4MP (QHD) and you're at 4 Mbps — double the storage. Jump to 8MP (4K UHD) and you're at 8 Mbps, quadruple the storage of a 1080p camera. For a 16-camera system, moving from 2MP to 4MP cameras roughly doubles your entire storage requirement. The resolution choices for the calculator cover 1MP (720p) through 12MP — with a custom pixel entry for cameras that don't fit a standard label.

Codec: the most under-appreciated storage lever

For the same resolution and quality, H.265 stores roughly half the data of H.264. H.265+ (smart codec, used by Hikvision, Dahua, and others) goes further — a 4MP H.265+ stream typically runs around 2.6 Mbps versus 4 Mbps for plain H.265 at the same quality. On a 16-camera system running for 30 days, that difference compounds to several terabytes. Older MJPEG recording eats 3–4× more storage than H.264 and should only be used where individual frame extraction quality is critical (forensic or court-evidence scenarios). All codecs — H.264, H.265/HEVC, H.264+, H.265+, and MJPEG — are selectable in the calculator, and brand-specific bitrate profiles are built in for Hanwha, Axis, Hikvision, Dahua, and others.

Recording mode: continuous vs motion vs scheduled

Continuous recording is the simplest to calculate but the most expensive in storage. Motion-triggered recording can cut storage by 50–80% for sites that are empty most of the day — a warehouse camera that only moves 20% of the time needs 80% less storage than if it were recording continuously. The calculator lets you set a motion activity percentage per camera group. Scheduled recording (e.g., business hours only, 10 hours/day instead of 24) is a middle ground for retail and office environments.

Retention days: 30 vs 60 vs 90 days changes everything

Retention is linear — 60 days of storage costs exactly twice as much as 30 days with the same cameras. Most commercial clients in Mumbai aim for 30 days as a baseline; banks and financial institutions often target 90 days to meet RBI guidelines; government and PSU projects can require 180 days or more. The quick-select chips in the calculator (7 / 15 / 30 / 60 / 90 days) make it easy to compare storage costs across different retention periods. For a breakdown of what Indian regulations require for different site types, see our dedicated guide on CCTV retention requirements in India.

A real example: 16-camera office in Andheri

Let's size a realistic Mumbai office setup: 16 cameras, mix of 2MP corridor cameras and 4MP lobby/entry cameras, H.265 codec, continuous recording, 30-day retention, 15% overhead margin.

• 8× 2MP cameras @ H.265 medium quality: ~2 Mbps each → 16 Mbps total
• 8× 4MP cameras @ H.265 medium quality: ~4 Mbps each → 32 Mbps total
• Combined: 48 Mbps → 6 MB/s → 518 GB/day → 15.5 TB for 30 days
• With 15% overhead: ~17.8 TB — use three 6 TB HDDs in the NVR

Switch those 4MP cameras to H.265+ (Hikvision or Dahua smart codec) at ~2.6 Mbps and the 30-day total drops to around 13.5 TB — fitting comfortably in two 8 TB drives instead of three 6 TB drives, without changing a single camera. Try both scenarios yourself using the CCTV HDD Storage Calculator — it lets you set different camera groups with different codecs side by side.

The reverse mode: how many days does my existing HDD give me?

The calculator also has a reverse mode — useful when an NVR is already specified or purchased. Enter the total available HDD capacity (in TB or TiB), set your camera groups, and it tells you exactly how many days and hours of footage that storage provides. This is the mode to use when a client hands you an existing NVR spec and asks how long it will record before overwriting.

What the calculator doesn't account for

• VBR vs CBR encoding — the calculator assumes CBR (constant bitrate) estimates. In practice most modern cameras use VBR, which can vary 30–50% from the estimate depending on scene complexity.
• Dual-stream recording — some NVRs record both a high-res main stream and a low-res sub-stream simultaneously. The sub-stream adds roughly 5–10% overhead.
• Audio recording — the calculator adds 64 kbps per camera when audio is enabled, which is the correct AAC/G.711 overhead.
• Remote viewing bandwidth — this is separate from storage and depends on your network, not covered here.

For the most accurate estimate, always enter the actual camera bitrate from the manufacturer spec sheet using the manual override option in the calculator. For mixed installations across several sites in Mumbai or Andheri, contact us for a full storage audit — we'll walk through every camera group and come back with an NVR and drive count you can quote on.