What this calculator works out
This calculator estimates recording storage from camera count, resolution, frame rate, codec and recording mode, and shows the requirement at retention periods from a week to three months.
Codec and recording mode change the answer more than resolution does. Moving from continuous H.264 to motion-triggered H.265+ can cut storage by a factor of ten.
Recording settings
Important
Actual CCTV storage varies by scene movement, bitrate settings, night vision noise, compression and recording schedule. This planner is a practical estimate, not a guarantee.
Before you size a recorder
- Frame rate affects storage proportionally and affects usefulness far less than people assume. 15 fps is smooth enough for identification.
- Motion recording saves a great deal in quiet locations and much less in busy ones, where it may trigger almost continuously.
- H.265 roughly halves the bitrate of H.264 at similar quality, and smart compression variants save more again on static scenes.
- Check the recorder supports the codec before choosing it. Older units may not.
Under UK data protection law, CCTV footage of identifiable people is personal data, and it must not be kept longer than necessary for the purpose. Many domestic and small business systems default to overwriting after 30 days, which is a reasonable and defensible period. Keeping months of footage without a stated reason is harder to justify.
How this calculator works
Bitrate per camera, scaled to the array and the period:
Mbps per camera = (megapixels × 0.9) × (fps ÷ 15) × codec factor × mode factor + audio
TB per day = Mbps × cameras × 86,400 ÷ (8 × 10⁶)
Requirement at each retention period = TB per day × daysThe codec factors are 1 for H.264, 0.55 for H.265 and 0.4 for smart compression. Mode factors are 1 for continuous, 0.45 for motion in a busy area and 0.25 for motion in a quiet one. Both multiply, so the combined saving compounds.
Worked example: four 1080p cameras
Using the default figures — 4 cameras at 1080p, 15 fps, H.264, continuous recording, no audio:
- About 0.08 TB per day
- At 30 days: roughly 2.3 TB
2.3 TB for a month, which a single drive covers. Switch to H.265+ and motion recording in a quiet area and the same cameras need around 0.23 TB for the month — a tenth of the storage. Move instead to 4K continuous H.264 and it becomes 9.3 TB. The three settings that cost nothing to change matter more than the drive that does.
Common mistakes
- Recording at maximum frame rate. 25 or 30 fps roughly doubles storage over 15 for little practical gain.
- Using motion recording in a busy area. It may trigger almost continuously.
- Choosing a codec the recorder does not support. Check before buying cameras.
- Keeping footage indefinitely. It is personal data and retention must be justified.
- Forgetting the drive's own overhead. Size for the requirement plus headroom.
Frequently asked questions
What are my legal obligations with home CCTV?
If cameras capture images beyond your own property boundary — a pavement, a neighbour's garden, a shared area — data protection law applies. The ICO publishes specific guidance for domestic CCTV covering signage, retention, responding to requests from people captured, and using the system in a way that respects others' privacy. Cameras entirely within your own boundary fall outside it.
How long should I keep footage?
Only as long as needed for the purpose. Thirty days is a common and defensible default for domestic and small business use — long enough to notice an incident and retrieve the recording, short enough to be proportionate. Systems that overwrite automatically at a set period are easier to justify than ones retaining indefinitely.
Do I need to tell people they are being recorded?
Where the system captures areas beyond your boundary, signage is expected and is part of the ICO's guidance. It also tends to reduce disputes with neighbours, which are the most common problem domestic CCTV creates. Discussing camera positions with neighbours before installing is worth more than any sign.
Should I use cloud or local recording?
Local recording keeps footage under your control and continues working without internet, but is vulnerable to the recorder being stolen — which is a realistic scenario for a burglary. Cloud recording survives that and depends on the connection and a subscription. Many systems do both, which addresses the weakness of each.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- Information Commissioner's Office — domestic CCTV guidance, retention and the rights of people recorded
- National Cyber Security Centre — securing connected cameras and network-attached devices
Sources are checked at publication and can change — how I choose and check references.