How Much Storage Do I Need for CCTV? UK Guide 2026

Each camera needs roughly its bitrate in Mbps × 10.8 GB per day of continuous recording. Multiply that by the number of cameras and the days you want to keep, then add about 20% headroom. For example, four cameras at 4 Mbps kept for 30 days need around 6.2TB, which means buying an 8TB drive rather than a 6TB one. Bitrate, not megapixels, drives that figure, so check what your cameras are actually set to before you choose a drive.

How much storage does CCTV use per camera per day?

Each camera uses about 10.8 GB per day for every 1 Mbps of bitrate when recording around the clock, so a 4 Mbps stream fills roughly 43.2 GB daily.

The 10.8 comes from simple unit conversion. A day has 86,400 seconds. Multiplying the bitrate in megabits by 86,400, dividing by 8 to get megabytes, then dividing by 1,000 to get gigabytes gives Mbps × 10.8.

Turning that into a drive size

To size the whole system, use this formula:

GB/day per camera × number of cameras × retention days × 1.2

The 1.2 adds 20% headroom for bitrate spikes at night, in rain or with moving foliage. For example, four cameras at 4 Mbps kept for 30 days need 43.2 × 4 × 30 = 5,184 GB. With headroom, that becomes about 6.2 TB. If you're working out how many cameras an office needs before doing this sum, our room-by-room guide to office CCTV cameras covers that step.

Drives are sold in decimal terabytes (1 TB = 1,000 GB), but many NVRs display binary tebibytes. As a result, a 4 TB drive shows as roughly 3.64 TiB. Formatting also takes some space. eufy notes that a 4TB drive doesn't give you 4TB of usable storage, so don't size right up to the label.

Days of recording per 1 TB

The table uses 1,000 ÷ (10.8 × Mbps × cameras) and assumes continuous 24-hour recording with no headroom. The bitrates are planning assumptions, not specifications for any particular camera. Check the actual stream setting in your NVR or camera menu and read across from there.

Bitrate (assumed)	1 camera	4 cameras	8 cameras
2 Mbps (21.6 GB/day each)	46.3 days	11.6 days	5.8 days
4 Mbps (43.2 GB/day each)	23.1 days	5.8 days	2.9 days
6 Mbps (64.8 GB/day each)	15.4 days	3.9 days	1.9 days
8 Mbps (86.4 GB/day each)	11.6 days	2.9 days	1.4 days
16 Mbps (172.8 GB/day each)	5.8 days	1.4 days	0.7 days

To scale it, multiply by your drive size. Eight cameras at 4 Mbps get about 2.9 days per terabyte, so a 4 TB drive gives roughly 11–12 days before overwrite. Allow less once formatting and the 20% margin are taken off. Motion-only recording stretches these figures, but by how much depends entirely on how busy each scene is.

What does a 4-camera shop need for 30 days?

Four cameras recording continuously at 4 Mbps need about 5.2TB for 30 days, or roughly 6.2TB once you add 20% headroom.

The continuous-recording walkthrough

At 4 Mbps, one camera writes 43.2 GB per day. Four of them together write 172.8 GB a day, and 30 days of that comes to 5,184 GB, which is about 5.2TB.

Adding an optional 20% planning allowance brings the target to about 6.2TB. It gives some slack for a busy day, a camera whose bitrate climbs at night, and the space the recorder keeps for itself. It does not guarantee a set number of days.

The same shop on motion-only recording

The figures below are an illustration, not a measurement. They assume each camera records for 30% of the day. Real motion share depends on footfall, the scene and how sensitive the detection is set.

Recording mode	Per day (4 cameras)	30 days	With 20% headroom
Continuous, 4 Mbps	172.8 GB	5,184 GB (≈5.2TB)	≈6.2TB
Motion-only, 30% of the day (assumed)	≈51.8 GB	≈1,555 GB (≈1.6TB)	≈1.9TB

On that assumption, the shop needs about 1.9TB instead of 6.2TB. If the shop is busy all day, motion recording saves far less, because the cameras trigger almost constantly.

Choosing the drive size

Drives come in fixed capacity steps, so round up to the next step above your target. At a steady 4 Mbps, a 6TB drive holds the 5.2TB the shop needs, but it falls short of the 20% allowance. If you want that margin, choose the next size up.

Before you buy, check two things on the NVR's datasheet:

• the largest drive it supports in each bay
• how many bays it has

If the recorder can't take one drive that size, you can split the capacity across two bays instead. Once the system is running, check the retention the recorder actually reports, because real bitrates rarely sit exactly at the planned figure. The same maths applies to larger sites. Our UK buyer's guide to CCTV cameras for schools covers camera choice once the camera count gets bigger.

Clear Security sells the equipment only. Have the cameras and cabling installed by your own electrician or by an independent installer accredited by NSI or SSAIB.

How do you size an 8-camera business site?

Multiply one camera's daily footage by eight and by the retention days, then add 20% headroom. Eight 4 Mbps cameras kept for 30 days need about 12.4TB.

At 4 Mbps, each camera writes 43.2 GB a day. Eight cameras produce 345.6 GB/day and 10.37TB over 30 days, which matches the 8-camera example in the ProDisk planner.

That planner holds back a 10% reserve. We plan with an optional 20% allowance (about 12.4TB) because variable-bitrate streams rise with rain, night-time noise and busy scenes, and many sites add a camera or two before anyone replaces the drives. Treat it as a planning cushion rather than a guarantee, and check the retention your recorder reports once the system is running.

When the bitrate goes up

The maths scales in a straight line. At 6 Mbps, one camera writes 64.8 GB a day, so eight cameras need 15.55TB for 30 days, or roughly 18.7TB with headroom. If you're deciding whether higher-resolution cameras justify that jump, our guide to when 4K CCTV camera systems pay off weighs the image gain against the extra storage.

Eight cameras, 30 days	4 Mbps	6 Mbps
Per camera per day	43.2 GB	64.8 GB
All cameras per day	345.6 GB	518.4 GB
30-day total	10.37TB	15.55TB
With 20% headroom	~12.4TB	~18.7TB

Single disks or RAID 6

Independent disks give you every terabyte you paid for but no protection. If one drive fails, the footage on it is lost. The same planner shows RAID 6 across four 8TB drives surviving any two drive failures.

That protection uses up two drives' worth of space for parity, so 32TB of raw disk gives about 16TB usable. This covers the 4 Mbps case with room to spare but falls short at 6 Mbps, where you'd need larger drives or more bays. Expect the recorder to show slightly less than the label, too, because an 8TB drive reports about 7.3TB in binary units.

Choose surveillance-rated drives built for continuous 24/7 writing rather than desktop disks. RAID support depends on the recorder model, so check its datasheet for the RAID levels it offers and the number of bays they need.

Motion recording or continuous: how much does it save?

Motion recording can cut storage dramatically, but only where the scene is quiet. A busy shop floor, swaying trees or passing traffic can trigger recording so often that usage approaches continuous.

The planning figures in the cctvinfo storage guide show the potential gap. It puts a 4K camera at roughly 50 GB a day continuous against about 5–10 GB on motion only. For 1080p, the figures are around 12 GB continuous against 1.5–3 GB on motion.

Those motion figures assume motion-only triggers on a fairly calm view. They are not a guarantee for every camera on site.

What moves the number

• Codec. H.265 is usually lighter than H.264 at similar picture quality. Check codec support when shortlisting models in our UK CCTV camera comparison guide.
• Scene complexity. Foliage, rain, headlights and crowds all add both triggers and bitrate.
• Lighting and settings. Low light, sensitivity levels, pre- and post-record times and frame rate all change the result.

Because so much depends on the site, eufy advises treating any calculator output as a planning estimate. It is not a fixed answer.

Where each mode fits

As general practice, record continuously on entrances, tills and cash points, where a gap in footage is costly. Motion recording suits low-activity areas such as rear yards, stores and corridors.

A common compromise is to run the main stream continuously while using motion-based or scheduled rules on the sub-stream. Another option is to schedule continuous recording only during opening hours.

Adding motion share to the formula

To work out how much storage your CCTV needs once motion recording is involved, multiply the continuous daily figure by the share of the day you expect to be recorded:

Storage = continuous GB per camera per day × motion share × cameras × retention days × safety margin

For example, a motion share of 0.3 means about 30% of the day is recorded. A margin factor of 1.2 adds 20% headroom. Estimate the motion share pessimistically for busy views, then round up to the next drive size rather than down.

Is 30 days the right retention period under UK GDPR?

Thirty days is a common planning figure, not a legal requirement. UK GDPR sets no fixed retention number for CCTV, and the ICO's CCTV guidance asks that footage be kept no longer than necessary for the purpose you have stated.

That purpose decides the period. A shop that needs time to spot stock loss, or a business whose insurer expects footage to be available after a claim, may justify longer. A driveway camera covering an obvious incident may need far less. Whatever period you choose, write down why.

Let retention set the drive size

Data minimisation means a longer period needs a documented reason. A recorder that overwrites its oldest footage on a rolling loop is the easiest setup to defend, because nothing builds up beyond the period you chose.

Storage grows in direct proportion to time, so moving from 30 to 60 days roughly doubles the capacity you need. Decide the period first, then size the drive to match it.

Oversizing causes a quieter problem. If the drive holds 90 days but your policy says 30, the system is keeping footage you have no stated reason to hold. Many NVRs have a maximum-recording-days or expiry setting. Use it so the recorder enforces your policy.

What to have in place

• Signage at the edge of the covered area, telling people that recording is taking place and who is responsible for it.
• A retention note in your CCTV policy, stating the period, the reason for it and who can change it.
• An export process, so that footage of an incident is copied off the recorder before the loop overwrites it. That copy then has its own documented reason to be kept.

Controller duties, subject access requests and domestic-versus-business scope are covered in our separate guides to GDPR and CCTV, so this section deals only with retention and storage.

How do you choose drive capacity with 20% headroom?

Multiply each camera's real daily footage by the number of cameras and the days you keep, add 20%, then round up to a drive size your recorder accepts.

The five-step sequence

1. Read the actual bitrate of each camera. Check the recorder's channel information or the camera's stream settings. The resolution on the box is not a reliable guide. GW Security puts the principle plainly: storage scales linearly with bitrate and time.
2. Convert to GB per day, then multiply by the camera count. One Mbps streamed for 24 hours is about 10.8 GB.
3. Multiply by retention days.
4. Multiply by 1.2.
5. Round up to the next drive or array size the recorder supports. The maximum capacity per bay is listed on the recorder's datasheet.

Here is a worked example. Take eight 1080p cameras recording continuously at roughly 12 GB a day each, the figure the cctvinfo storage guide gives. Over 30 days they need 2,880 GB, and with headroom that rises to about 3.5 TB, which points to a 4TB drive.

Why add 20%?

The 20% is Clear Security's house guidance, not an industry standard. It covers the gap between a spreadsheet figure and how a recorder actually behaves:

• Formatting loss. Drive makers count capacity in decimal units, while many recorders report it in binary. A 4TB drive therefore shows as roughly 3.6TB once installed.
• Night-time peaks. When IR switches on, sensor noise rises. A camera on variable bitrate encodes that noise as extra data, so measure the bitrate after dark as well as by day.
• Camera additions. Without spare space, adding one more camera later eats straight into your retention days.
• Drive wear and replacement. A replacement of the same nominal size from a different model line may format slightly smaller. Headroom absorbs that difference.

Single large drive or RAID?

A single drive is the simplest and cheapest setup per terabyte. The drawback is that when it fails, every day of footage on it goes too.

RAID 5 needs three or more drives and survives one drive failure, at the cost of one drive's capacity. RAID 6 needs four or more and survives two failures, at the cost of two drives' capacity.

So four 4TB drives give roughly 12TB usable in RAID 5, or 8TB in RAID 6. Apply your 1.2 multiplier to the usable figure, not the raw total. Also confirm the recorder offers RAID at all, because not every multi-bay NVR does.

RAID is not a backup. It protects against a drive failing, but not against:

• the recorder being stolen
• a fire
• clips being overwritten when retention rolls over

Export any footage you need to keep to separate storage.

Drives ordered with a recorder are supplied pre-fitted before dispatch. You can browse the range at Clear Security or ask us for a suggested system built around your own numbers.