How Much Storage Do You Need for Your CCTV System?

What matters in practice:

• Storage (GB) = Bitrate (Mbps) × 10.8 × cameras × days — one megabit per second of continuous recording uses about 10.8 GB per day.
• H.265 roughly halves the requirement compared with H.264, so four cameras for 30 days drops from about 5.2 TB to about 2.6 TB.
• Add 10–20% headroom — drives report less capacity than the box claims, and busy scenes use more bitrate than the average.

🧮 Interactive Tool: Use our free CCTV Storage & NVR Sizing Calculator to turn camera counts, bitrates and retention days into exact hard drive sizes.

The most common mistake in setting up CCTV is buying a hard drive before working out how much footage you actually need to keep. Too little storage means footage is overwritten before you can use it. Too much means paying for capacity you never touch. The good news is that the maths is simple.

The four things that decide storage

1. Number of cameras. Each camera records its own stream.
2. Resolution and bitrate. Higher resolution means a bigger stream. A 2MP (1080p) camera typically runs at 2–4 Mbps, while an 8MP (4K) camera runs at 4–8 Mbps or more.
3. Compression. H.265 (and "smart" variants such as H.265+) uses roughly 30–50% less space than H.264 at similar quality — see our breakdown of H.265 video compression savings for the detail.
4. Retention and recording mode. How many days you keep footage, and whether cameras record all the time or only on motion.

The simple formula

One megabit per second of continuous recording uses about 10.8 GB per day. So:

Storage (GB) = Bitrate (Mbps) × 10.8 × Number of cameras × Days of retention

For example, 4 cameras at 4 Mbps, kept for 30 days: 4 × 10.8 × 4 × 30 = 5,184 GB, or about 5.2 TB. Switch to H.265 at 2 Mbps and the same system needs about 2.6 TB.

For a fuller methodology — frame rates, motion factors, safety margins and RAID overhead — see our guide to calculating NVR storage pools.

Quick reference table

Figures assume 24/7 recording and are rounded. Add 10–20% headroom.

That last row shows why large systems often use motion-based recording or tiered retention, which we cover in how to cut CCTV storage costs without losing evidence quality.

How motion recording changes the numbers

If your cameras only record when something moves, actual usage depends on how busy the scene is. A quiet side entrance might record 10–20% of the day. A shop floor or road-facing camera may record 60% or more. Use 30–50% as a cautious planning figure if you are unsure, and watch real usage for a few weeks.

Practical tips

• Check your recorder's own calculator. Many DVR and NVR brands have one, and it uses their exact bitrates.
• Check the maximum drive size your recorder supports. Many entry-level units cap at 6, 8 or 10 TB per bay, and some at less.
• Plan for growth. If you may add cameras later, buy a recorder with spare bays.
• Verify after setup. Look at the recorder's HDD information page, which usually shows how many days of footage it can hold at current settings.

Worked example: a small shop

A corner shop has six cameras: four 2MP cameras inside and two 4MP cameras covering the entrance and car park. The owner wants 45 days of footage using H.265.

• The four 2MP cameras run at about 2 Mbps each, for a total of 8 Mbps.
• The two 4MP cameras run at about 3 Mbps each, for a total of 6 Mbps.
• Combined bitrate is 14 Mbps.
• 14 × 10.8 GB per day = about 151 GB per day.
• 151 GB × 45 days = about 6.8 TB.

Adding 15% headroom brings the figure to roughly 7.8 TB, so an 8 TB drive is just enough, and a 10 TB drive gives a comfortable margin. If the shop closes at night and the interior cameras switch to motion recording overnight, real usage will be lower.

Why the number on the box is not the number you get

Drive makers count a terabyte as 1,000,000,000,000 bytes, while many operating systems and recorders report capacity in binary units, so a 4 TB drive often shows as about 3.6 TB. Formatting and file system overhead take a little more. This is another reason to add 10–20% headroom rather than sizing exactly.

Common bitrate mistakes

• Assuming the camera's maximum bitrate is the average. With variable bitrate, busy scenes spike while quiet scenes use far less. Check actual figures in the recorder's status page after a week.
• Forgetting audio. If microphones are enabled, audio adds a small but real amount, usually well under 0.1 Mbps per camera.
• Mixing up megabits and megabytes. Bitrates are in megabits per second (Mbps), and storage is in gigabytes. A bit is one-eighth of a byte, which is already built into the 10.8 GB per day figure.
• Ignoring night mode. Infrared night footage can use more bitrate because of image noise, especially on cheaper cameras. Measure night use separately if your site is busy after dark.

Check your estimate in the real world

After the system has run for a week, open the recorder's storage or HDD page and note how much space has been used. Divide used space by the number of days to get your true daily figure, then compare it with your estimate. Adjust bitrates, frame rates or retention if the numbers are far apart.

The bottom line

Decide how many days of footage you need, check your camera bitrates, apply the formula, and round up. Then choose a drive designed for continuous recording: surveillance vs desktop drives explains which class of drive to buy. Households and businesses usually land in slightly different places, so our homeowner's guide to CCTV storage and how long a business should keep footage are worth reading before you order.

Next Steps

Backspace Business Solutions designs and installs surveillance systems, including CCTV and biometric solutions, with storage sized to your cameras and retention requirements.

Message us on WhatsApp or request a free site assessment and we will work out the drive size your system actually needs.