How CCTV Storage Is Calculated
The calculator starts with the recorded bitrate, not the camera resolution alone. It converts Mbps from bits to bytes, multiplies by the actual recording time and number of cameras, then adds your selected overhead percentage.
Storage bytes = bitrate (bits/second) × recording seconds × cameras ÷ 8
Recording seconds = days × recording hours/day × 3,600
This site uses decimal storage units: 1 GB = 1,000,000,000 bytes and 1 TB = 1,000 GB.
What Bitrate Should I Use?
Use the bitrate configured in the camera or recorder when possible. Actual bitrate depends on several settings and on what the camera sees, so two cameras with the same resolution can still use very different storage.
- Resolution
- Frame rate
- Codec
- Scene complexity and movement
- Camera quality/configuration
- Constant vs variable bitrate
H.264 vs H.265
H.265 can often reduce the bitrate needed for comparable visual quality versus H.264, which can reduce bandwidth and storage. The reduction is not a guaranteed percentage. Encoder quality, firmware, resolution, motion, frame rate, GOP settings, and image-quality targets all matter. For that reason, the calculator does not apply a fixed H.264 or H.265 multiplier.
Continuous vs Motion Recording
Continuous recording has predictable recording hours, so it is easier to estimate. Motion or event recording can use much less storage when a scene is quiet, but the result depends on how often recording is triggered and how long each event lasts. If activity levels are unknown, use a conservative estimate rather than assuming a large saving.
Example CCTV Storage Calculation
Four cameras recording at 4 Mbps each for 24 hours per day over 30 days produce 5.184 TB of footage before overhead. Adding 10% overhead adds 0.5184 TB, producing a final estimate of 5.7024 TB, displayed as 5.70 TB. The next listed HDD capacity that is not below the requirement is 6 TB; 8 TB provides additional margin.
FAQ
How much storage does one CCTV camera use per day?
It depends mainly on the recorded bitrate and how many hours the camera records. For example, a camera recording continuously at 4 Mbps uses about 43.2 GB per 24-hour day before any storage overhead. A different bitrate or shorter recording schedule changes that number directly.
How much storage do 4 cameras need for 30 days?
There is no universal number without a bitrate. At 4 Mbps per camera, 24 hours per day, and 30 days, four cameras require 5.184 TB before overhead. With 10% overhead, the estimate becomes about 5.70 TB, so 6 TB is the minimum rounded HDD capacity in this calculator.
How much storage do 8 cameras need?
Eight cameras need roughly twice the storage of four cameras when bitrate, recording hours, and retention days are unchanged. Enter the actual bitrate and retention target above to calculate the total instead of relying on a camera-count-only estimate.
Does H.265 use less storage?
H.265 can often deliver similar visual quality at a lower bitrate than H.264 under comparable conditions, which can reduce storage. The saving is not fixed: camera firmware, scene movement, resolution, frame rate, quality settings, and bitrate mode all affect the result. This calculator therefore uses bitrate as the direct input.
Is 1TB enough for CCTV?
Sometimes, but not for every system. One low-bitrate camera with short retention may fit easily, while several cameras recording continuously can consume 1 TB quickly. Calculate the configured bitrate, camera count, hours, and required days before choosing a drive.
How many days can a 4TB HDD record?
It depends on the total recorded bitrate. As one reference point, four cameras at 4 Mbps each recording 24/7 would fill about 4 TB in roughly 23 days before overhead. If you reserve 10% planning overhead, the practical retention estimate is closer to 21 days. Other settings can be very different.
Planning note
Recorder drive compatibility, RAID behavior, filesystem reservations, camera bitrate spikes, audio, metadata, and vendor-specific storage behavior can change real-world retention. Treat the result as a planning estimate and verify the final recorder configuration before purchasing storage.