How to Calculate NVR CCTV Storage Capacity: Formula, Example, and the Effect of H.265

To calculate NVR CCTV storage capacity, multiply one camera's bitrate (Mbps) by 3,600 seconds, recording hours per day, retention days, and number of cameras, then divide by 8 and by 1,000 to get gigabytes (GB). The result is the baseline requirement. Add headroom and account for RAID before choosing hard disk sizes.

Many NVRs stop recording sooner than promised, or overwrite old footage before the requested retention period is reached. The most common cause is that disks were chosen by habit instead of by calculation. This article shows the formula, the factors that move the numbers, and one worked example with steps you can repeat.

Numbers in the example are illustrative, not a standard and not a guaranteed result. Real bitrate depends on the camera, its settings, and the site. For a survey and quotation, see our CCTV installation service or contact our team.

What Is NVR CCTV Storage Capacity and Why Calculate It?

NVR CCTV storage capacity is the total hard disk space needed for all cameras to record throughout the retention period you set. An NVR (Network Video Recorder) is a device that receives digital video streams from IP cameras over the network and stores them on hard disks. CCTV hard disk requirement is the calculated figure plus spare headroom.

Calculate before buying, because two mistakes both cost money. A disk that is too small overwrites footage faster than your retention policy, so evidence of an incident can be gone when it is needed. A disk that is too large raises cost for space that is never used.

The calculation also forces answers to questions that are often left open: how many days of footage must be kept, do all cameras record continuously, and is redundancy needed. For general system planning, see the office CCTV security system installation guide.

How Do You Calculate NVR CCTV Storage Capacity?

The base formula: capacity (GB) = bitrate (Mbps) x 3,600 x recording hours per day x days x number of cameras / 8 / 1,000. Bitrate is in megabits per second (Mbps). The 3,600 converts seconds to hours. Dividing by 8 converts megabits to megabytes (MB), and dividing by 1,000 converts megabytes to gigabytes (GB).

If all cameras use the same bitrate, apply the formula directly. If they differ, calculate per camera group and add the results. For example, indoor cameras with a low bitrate are calculated separately from lobby or gate cameras with a higher bitrate.

Units must stay consistent. Camera datasheets often give bitrate in kbps or Mbps, so convert to Mbps first (1,000 kbps = 1 Mbps). The formula uses powers of 1,000 because disk makers define 1 TB as 1,000 GB. The difference from a 1,024 count is covered in the TB and TiB section below.

What Determines CCTV Camera Bitrate?

CCTV camera bitrate is the amount of video data a camera sends each second, measured in Mbps. It is not a fixed built-in value but the result of several settings and site conditions. Two cameras with the same resolution can therefore produce different disk requirements.

The most reliable way to get the real figure is to read the bitrate shown by the camera or NVR under site conditions, then use the highest reasonable value as the calculation basis.

H.265 vs H.264: How Does It Affect CCTV Hard Disk Needs?

H.264 and H.265 are two video compression standards commonly used by IP cameras. H.265 is designed to be more efficient, meaning that for comparable image quality it generally needs a lower bitrate than H.264. A lower bitrate means the formula above gives a smaller disk requirement.

The size of the saving cannot be stated as a single number. Codec efficiency varies by scene, the quality of the camera's encoder, and the settings chosen. That is why this article gives no percentage. Use the camera datasheet and, where possible, measure the real bitrate on site.

Two practical points. First, confirm that the NVR and playback software support the codec the camera uses. Second, cameras often have variants such as H.265+ or vendor smart modes. These change bitrate in ways that differ between brands, so calculate from measured bitrate, not from brochure claims.

What Does a Worked Example Look Like for 16 Cameras and 30 Days?

The following example is illustrative: 16 cameras, 4 Mbps per camera, recording 24 hours a day, kept for 30 days. The 4 Mbps figure is only an assumption.

The 20% headroom in step 6 is an example choice for system space and bitrate spikes, not a rule. If recording is motion-only and motion occurs 40% of the time (also an assumption), the base requirement becomes 20.736 x 0.4 = 8.2944 TB.

How Many Days of CCTV Footage Fit on the Disks You Have?

If the disks already exist, reverse the formula to find how many days of CCTV footage fit: days = capacity (GB) / daily need of all cameras (GB). From the example above, one camera uses 43.2 GB per day, so 16 cameras use 43.2 x 16 = 691.2 GB per day.

With 32 TB of raw disk (32,000 GB), the base retention is 32,000 / 691.2 = about 46.3 days. That figure does not yet remove headroom and does not account for RAID.

How many days is enough is a policy decision, not a calculation. Some organizations keep two weeks, others a month or more, depending on risk, audit needs, and internal or contractual rules. Ask your security, legal, or audit team, then use the answer as an input to the formula. For sites with many branches, also see multi-location company CCTV installation with cloud.

Does an NVR Need RAID and Spare Disks?

RAID is a technique that combines several hard disks so the system keeps running when one disk fails. On an NVR that records continuously, disks work without pause, so disk failure is a risk worth planning for.

Redundancy reduces usable capacity. In RAID 5, one disk is used for parity, so effective capacity = (number of disks - 1) x disk size. In RAID 1, data is mirrored, so effective capacity is only half.

Continuing the example: a 24.9 TB requirement with 8 TB disks. In RAID 5, effective capacity must be at least 24.9 TB, so (N - 1) x 8 >= 24.9, or N - 1 >= 3.11, meaning N - 1 = 4 and N = 5 disks. Four 8 TB disks give only 24 TB effective, which is not enough. Disk redundancy does not replace an off-site copy for very important footage.

Why Does an 8 TB Hard Disk Show Less Than 8 TB on a Computer?

Disk makers define 1 TB as 1,000,000,000,000 bytes (a power of 10). Operating systems often count in powers of 2, where 1 TiB = 1,099,511,627,776 bytes, but display it with a TB label. As a result a disk labeled 8 TB shows about 7.28 in the units the operating system uses, even though no space is missing.

The formula in this article divides by 1,000 to match the manufacturer's label. Expressed in TiB, the example result is about 18.86, which is 20.736 divided by 1.0995.

A gap of about 9% at terabyte scale is enough to break a very tight calculation. So compare the result with the capacity labeled by the manufacturer, not with the figure shown on an operating system screen. Space used by the file system and metadata also reduces capacity, which is one reason to add headroom to the final result.

8-Step Checklist for Sizing CCTV Hard Disks

Use the following order before buying or adding NVR hard disks. Each step produces a number or decision that feeds the next, so do not skip steps one to three.

1. Set the retention period in days together with the responsible party, instead of guessing.
2. List every camera with its resolution, fps, codec, and location, then group those with the same settings.
3. Take each group's bitrate from the datasheet or, better, from measurement on site.
4. Decide the recording mode: continuous, motion only, or mixed per camera.
5. Calculate each group's capacity with the formula, then add them up.
6. Add headroom for the file system and bitrate spikes.
7. Decide RAID or redundancy, then compute the number of disks so effective capacity still meets the need.
8. Check the NVR's number of disk bays and maximum supported disk size, and verify the result after a few days of recording.

Common Mistakes When Calculating CCTV Hard Disk Needs

The most frequent errors come from assumptions that were never checked. Watch for these six before handing a number to the supplier.

• Using the brochure bitrate. A maximum or typical figure is not necessarily what your site produces.
• Treating all cameras alike. A gate camera and a corridor camera rarely share the same bitrate.
• Forgetting unit conversion. Mixing kbps, Mbps, MB, and GB is the largest source of error.
• Ignoring RAID. Raw capacity is not effective capacity.
• Leaving no headroom. A disk filled exactly to the calculated limit has no room for spikes or added cameras.
• Not testing. After a few days of recording, compare real disk usage with the calculation and adjust.

If your site is a factory with many points and changing light, bitrate tends to vary more. For industrial sites, see CCTV installation for factories in Bekasi and Karawang.

Frequently Asked Questions

How do you calculate NVR CCTV storage capacity?

Multiply bitrate (Mbps) by 3,600, recording hours per day, days, and number of cameras, then divide by 8 and 1,000 to get GB. Add headroom and account for RAID if used. Compare the final figure with the capacity labeled by the manufacturer.

How much hard disk do 16 CCTV cameras need?

It depends on bitrate, recording hours, and retention. In this article's illustrative example (4 Mbps, 24 hours, 30 days), the base requirement is 20.736 TB. Recalculate with your own cameras' bitrate.

Is H.265 always more economical than H.264?

H.265 is generally more efficient, but the size of the saving varies by scene and camera encoder, so we give no percentage. Check the camera datasheet and measure real bitrate.

Does motion-only recording save disk space?

Usually yes, because the camera stores footage only when motion occurs. The amount depends on how often motion happens at the site, and there is a risk of undetected events. Measure motion patterns before relying on it.

Why does an 8 TB hard disk show less than 8 TB?

Manufacturers count 1 TB as 1,000 GB, while operating systems often count with 1,024. About 7.28 TiB from an 8 TB disk is a unit difference, not damage.

How do I request a CCTV survey and quotation?

Contact our team through the contact page for a survey and quotation. An overview of the service is on the CCTV service page.