How Much HDD Storage Do You Need for CCTV Recording?

Picking the wrong hard drive is one of the most common mistakes people make when setting up a CCTV system. Get it wrong on the low side, and your footage gets overwritten after just a few days — right when you actually need to pull up last week’s recording. Get it wrong on the high side, and you’ve spent extra money on capacity you’ll never touch. The good news is that CCTV storage calculation isn’t guesswork. It comes down to one formula:

Required CCTV storage (GB) = Camera bitrate (Mbps) × Number of cameras × Recording hours per day × Number of recording days ÷ 8,000

Here’s what each part means: bitrate is how much data your camera generates per second, measured in megabits per second (Mbps) — this depends on resolution, frame rate, and compression. Number of cameras is simply how many channels are recording. Recording hours per day accounts for whether you’re recording 24/7 or only during certain hours. Recording days is how long you want to keep footage before it gets overwritten. Dividing by 8,000 converts the total from megabits into gigabytes (since there are 8 bits in a byte, and 1,000 megabits ≈ 1 gigabit, with some rounding for simplicity).

Keep in mind this is a planning formula, not a guarantee — actual storage use varies with codec (H.264 vs H.265), resolution, frame rate, motion-based vs. continuous recording, and scene complexity. Use it to get in the right ballpark, then round up.

What Determines CCTV Storage Requirements?

Several variables combine to decide how fast your hard drive fills up. It helps to split them into two groups.

Camera-Side Factors

• Number of cameras — more channels recording simultaneously means more total data.
• Camera resolution — 2MP, 4MP, 5MP, and 8MP (4K) cameras each generate different amounts of raw video data. See AMCOM’s IP Camera range for resolution options from 2MP to 8MP.
• Video bitrate — the actual output rate of the camera stream; this is the number that really drives storage, not resolution alone.
• Compression codec — H.264 and H.265 compress footage differently, with H.265 generally producing smaller files at similar quality.
• Frames per second (FPS) — higher FPS means smoother video but more data per second.
• Audio recording — if enabled, audio adds a small but real amount to the total bitrate.
• Camera configuration and scene complexity — a camera pointed at a busy street corner generates more data than one facing a quiet hallway, because more motion means more encoded detail.

Recording-Side Factors

• Continuous vs. motion-based recording — recording only on motion can cut storage needs dramatically compared to 24/7 recording.
• Recording hours per day — a shop that only records during business hours needs far less storage than a warehouse recording around the clock.
• Number of CCTV recording days — your desired retention period, whether that’s 7 days, 30 days, or 90 days.

Understanding these factors matters because two systems with the same number of cameras can have wildly different storage requirements depending on how they’re configured.

CCTV Storage Calculation Explained

At its core, the calculation follows this logic:

Storage = Bitrate × Cameras × Recording Time × Retention Period

Converting Mbps to GB

Camera bitrate is usually listed in Mbps (megabits per second). To turn that into a real-world storage number, you multiply it out across every camera, every recording hour, and every day you want to keep footage — then convert the result from megabits to gigabytes.

Example Setups by Camera Count

Let’s put this into practice with a few common setups, using realistic assumed bitrates (actual bitrates vary by manufacturer and settings, so always check your camera’s spec sheet — AMCOM’s 5MP Smart Hybrid Network Bullet Camera is a good reference point for a mid-range setup):

• 4 cameras at 4 Mbps each, recording 24/7 for 30 days: roughly 518 GB
• 8 cameras at 4 Mbps each, recording 24/7 for 30 days: roughly 1,036 GB (about 1 TB)
• 16 cameras at 4 Mbps each, recording 24/7 for 30 days: roughly 2,073 GB (about 2 TB)
• 32 cameras at 4 Mbps each, recording 24/7 for 30 days: roughly 4,147 GB (about 4 TB)

These figures assume continuous recording at a moderate bitrate. Switch to motion-based recording or a lower resolution, and your actual numbers could come in well under these estimates.

CCTV HDD Calculation Example

Worked examples make this easier to apply to your own setup.

Example 1: 8 Cameras Recording 24/7 for 30 Days

Assume each camera runs at 4 Mbps. Combined bitrate: 4 Mbps × 8 cameras = 32 Mbps.

Step-by-Step Breakdown

Over 24 hours, that’s 32 Mbps × 3,600 seconds × 24 hours ÷ 8 (bits to bytes) ÷ 1,000 (MB to GB) ≈ 34.5 GB per day. Over 30 days: 34.5 GB × 30 ≈ 1,036 GB, or roughly 1 TB.

Quick Takeaway

Round up slightly for a safety margin — an AMCOM 2HDD NVR comfortably covers this setup.

Example 2: 16 Cameras Recording 12 Hours per Day

Same 4 Mbps bitrate, but only 12 hours of recording instead of 24, for 30 days: this roughly halves the daily data compared to 24/7 recording, landing around 1 TB instead of the 2 TB you’d need for round-the-clock recording on the same camera count. Reducing recording hours is one of the simplest ways to cut storage costs when continuous monitoring isn’t necessary.

Example 3: Motion-Based Recording

Take the same 16-camera setup, but switch from continuous to motion-triggered recording. If cameras are only actively recording during 20–30% of the day (typical for a low-traffic office after hours), storage needs can drop to a fraction of the continuous-recording figure — often 60–80% less, depending on how much activity the space actually sees. This is why motion detection is one of the most effective storage-saving features available, especially for sites with long quiet periods.

How Much Storage Do You Need for CCTV?

Here’s a quick-reference table for common setups. Treat these as planning estimates — your actual CCTV recording storage will depend on your specific camera and NVR configuration.

For setups at the larger end of this table, AMCOM’s 4HDD, 8HDD, and 16HDD NVRs give you room to scale without hitting a capacity wall.

How Resolution Affects CCTV Recording Storage

Camera resolution and storage needs are related, but resolution alone doesn’t tell the whole story.

Common Resolution Tiers

• 2MP / 1080p cameras produce the smallest files among common surveillance resolutions and are a reasonable baseline for homes and small offices — see AMCOM’s 2MP HD Cameras.
• 4MP cameras capture noticeably more detail and generally need a moderately higher bitrate to maintain image quality — see 4MP IP Cameras.
• 5MP sits a step above 4MP, useful where identifying faces or license plates from a distance matters — see 5MP IP Cameras and 5MP HD Cameras.
• 8MP / 4K cameras deliver the sharpest footage but come with the largest storage appetite, especially at higher frame rates — see 8MP IP Cameras.

The important nuance: resolution drives potential data volume, but the actual bitrate — shaped by compression, scene complexity, and frame rate — is what really determines how much space footage consumes. Two 4K cameras with different compression settings can produce very different file sizes for the same footage.

H.264 vs H.265: Which Uses Less Storage?

Compression codec is one of the biggest levers you have for controlling storage costs.

H.264 has been the surveillance industry standard for years. It’s widely compatible and well understood, but it’s less efficient than newer codecs at compressing video without losing quality.

H.265 (HEVC) is a newer codec designed to deliver similar visual quality at a lower bitrate. Under suitable conditions — decent hardware support and appropriate encoder settings — H.265 can meaningfully reduce both storage consumption and bandwidth usage compared to H.264. The exact savings depend heavily on scene content, encoder implementation, and configuration, so treat any specific percentage claim as an estimate rather than a guarantee. If your NVR and cameras support H.265, it’s generally worth using for storage-conscious installations. Check compatibility on AMCOM’s DVR and NVR pages before buying.

What Is an NVR Storage Calculator?

An NVR storage calculator is a tool that estimates how much hard drive capacity you’ll need based on your system’s actual configuration, rather than rough guesswork. To get an accurate estimate, you typically need to enter:

• Camera count
• Resolution
• Bitrate
• Frames per second (FPS)
• Recording hours per day
• Recording days (retention period)
• Compression codec
• Recording mode (continuous or motion-based)

Bitrate-based calculation is generally more reliable than estimating storage from resolution alone, because two cameras with identical resolution can still produce very different amounts of data depending on compression, frame rate, and how much motion they capture. If you only have resolution to go on, treat your estimate as a rough floor and add a safety margin. AMCOM’s Tools page is a good starting point if you’d rather run these numbers interactively than by hand.

Choosing the Right HDD for NVR

Once you know your target capacity, a few other factors matter when selecting the actual drive:

• Required storage capacity — based on your calculation above, with some buffer added.
• Number of cameras — more channels typically mean higher sustained write loads on the drive.
• Expected recording days — longer retention means either a bigger drive or a plan for multiple drives.
• 24/7 workload — surveillance drives run near-continuously, which is a different duty cycle than a typical desktop hard drive.
• NVR compatibility — check your NVR’s maximum supported HDD capacity and interface type before buying. AMCOM’s 1HDD and Management Server options cover different scales of deployment.
• Surveillance-rated HDDs — drives designed for continuous read/write cycles tend to hold up better over time than general-purpose drives.
• Future expansion — if you plan to add more cameras later, sizing up now can save a re-purchase down the line.
• Redundancy/RAID requirements — for larger or higher-stakes installations, RAID configurations (where supported) add a layer of protection against drive failure.

One important note: don’t select a hard drive based solely on your NVR’s maximum supported capacity. That number tells you the ceiling, not what you actually need — sizing should always start from your camera count, bitrate, recording hours, and retention period.

How Many CCTV Recording Days Can an HDD Store?

The same hard drive can provide very different retention periods depending on your setup. A 2TB drive might store 30 days of footage from four 2MP cameras recording continuously, but only 10–12 days if you scale up to eight cameras at higher resolution. Recording schedule matters too: switching from 24/7 to 12-hour recording roughly doubles the number of days a given drive can hold. Motion-based recording can stretch that even further, since only active periods consume storage.

If you already know how many days of footage you want to retain, you can work backward: take your desired retention period, multiply by your total daily data output (bitrate × camera count × recording hours), convert to gigabytes, and that tells you the minimum HDD size to look for.

Common CCTV Storage Calculation Mistakes

A few recurring errors lead to under- or over-buying storage:

• Calculating storage using resolution alone, ignoring actual bitrate
• Forgetting to factor in recording hours per day
• Assuming every camera records continuously when some may be motion-triggered
• Ignoring the storage savings motion recording can provide
• Not allowing extra capacity for future camera additions
• Selecting an HDD without checking NVR compatibility first
• Confusing advertised HDD capacity with actual usable capacity (formatting and system overhead reduce the real number slightly)
• Not clearly deciding on a retention period before shopping for storage

CCTV Storage Requirements for Different Applications

Storage needs vary by setting, and there’s no single number that fits every situation — it comes down to camera count, recording configuration, and how long you need to retain footage.

• Homes typically run fewer cameras and shorter desired retention, keeping storage needs modest.
• Small offices often add a few more cameras and may want 2–4 weeks of retention for insurance or dispute purposes.
• Retail stores (Chain Store Solution) frequently need longer retention to review incidents and returns, pushing storage requirements higher.
• Warehouses and industrial parks (Industrial Park Solution) often cover large areas with many cameras, and 24/7 recording is common for asset protection.
• Schools (School Solution) balance a higher camera count across a large campus with policies that may require extended retention.
• Banks (Bank Solution) and hospitals (Hospital Solution) typically require long retention periods for compliance and dispute resolution.
• Large commercial sites (Commercial Complex Solution) tend to combine high camera counts, continuous recording, and longer retention periods, making accurate storage planning especially important.

Rather than following a rigid one-size-fits-all number, work through the formula for your specific camera count and retention goals.

How to Calculate the Right NVR HDD Size

A simple step-by-step process to follow:

1. Count the cameras you’re installing.
2. Determine each camera’s bitrate (check the spec sheet or manual).
3. Decide on recording hours per day.
4. Decide how many CCTV recording days you need to retain.
5. Apply the storage formula: Bitrate × Cameras × Recording Hours × Recording Days ÷ 8,000.
6. Add reasonable extra capacity to account for configuration differences, audio, and future expansion.
7. Confirm your NVR’s supported HDD capacity and interface before purchasing.

Frequently Asked Questions

How much storage do I need for 4 CCTV cameras?

For four 2MP cameras recording continuously at roughly 4 Mbps each for 30 days, plan for around 500 GB, though motion-based recording can reduce this significantly.

How much storage do I need for 8 CCTV cameras?

At similar settings, eight cameras recording continuously for 30 days typically need around 1 TB.

How much storage do I need for 16 CCTV cameras?

Sixteen cameras under the same assumptions generally need around 2 TB for 30 days of continuous recording.

How long will 1TB store CCTV footage?

It depends on camera count and bitrate, but as a rough guide, 1TB can typically hold about 30 days of continuous footage from roughly 8 cameras at 2MP resolution.

How long will a 2TB HDD record CCTV?

Under similar assumptions, a 2TB drive can typically cover around 30 days for about 16 cameras, or longer for fewer cameras or motion-based recording.

How much storage does a 4K CCTV camera use?

4K (8MP) cameras generally require a notably higher bitrate than 2MP cameras, so expect meaningfully more storage per camera — the exact amount depends on compression and frame rate.

Is H.265 better for CCTV storage?

Generally yes — H.265 tends to reduce storage and bandwidth needs compared to H.264 under similar quality settings, though actual savings vary by configuration.

Can I add more HDD storage to an NVR?

Many NVRs support multiple drive bays or drive upgrades up to a maximum supported capacity, but this depends on the specific model — see AMCOM’s full NVR range for options from 1HDD to 16HDD.

How many days can CCTV footage be stored?

This is fully configurable based on your storage capacity and how much data your system generates daily — there’s no fixed limit beyond what your hardware and settings allow.

What size HDD is best for an NVR?

The best size is whatever your calculated storage requirement comes out to, plus a reasonable buffer — not simply the largest drive your NVR supports.

Planning Your Storage the Right Way

Getting CCTV storage calculation right comes down to balancing four things: recording retention, video quality, storage cost, and future scalability. Skimp on any one of them, and you either run out of footage history when you need it most, or you overspend on capacity that never gets used.

If you’re mapping out a new installation or expanding an existing one, working through camera count, bitrate, recording hours, and retention period upfront will save you a re-purchase down the line. For businesses looking to size their system properly, AMCOM NVR recording solutions offer a range of storage configurations built around exactly this kind of planning.

Before choosing your next NVR, take a few minutes to run the numbers: count your cameras, check their bitrate, decide on recording hours and retention days, and apply the formula — or get in touch with AMCOM for help sizing your system. It’s a small step that makes sure your CCTV system actually has the footage there when you need it.