To plan CCTV storage, start with how much video is written each second, how many cameras record, and how long recordings must remain available. Resolution alone cannot determine file size: codec, frame rate, scene movement and rate control also affect the stream. A measured average bitrate from the actual camera is a stronger input than a generic “1080p” preset.
Calculate a continuous-recording baseline
Consider eight cameras, each averaging 2 megabits per second, recording all day for 30 days. One camera writes 2,000,000 ÷ 8 = 250,000 bytes per second. Multiply by 86,400 seconds, 30 days and eight cameras: 5,184,000,000,000 bytes, or 5.184 decimal TB. With a 5% planning allowance for recording overhead, the result is about 5.44 TB. Enter the same assumptions in the CCTV Storage Calculator and compare its breakdown.
Drive capacities are usually advertised in decimal TB, whereas some interfaces display binary TiB. The NIST reference on decimal and binary prefixes explains why a terabyte and a tebibyte represent different byte counts. The 5.44 trillion-byte estimate is roughly 4.95 TiB. These are different labels for the same quantity of bytes; neither number by itself tells you how much capacity the recorder actually makes available after formatting, reserves or other data.
Account for the recording schedule
If a camera records only 12 hours per day at the same average bitrate, its video payload is roughly half the continuous baseline. Motion or event recording is less predictable: “60% active” is useful for a scenario estimate but can change with traffic, lighting, weather and sensitivity. Check whether pre-event and post-event buffers also record. Keep a conservative scenario alongside an optimistic one instead of planning all hardware around the lowest estimate.
Include every stream and audio track actually stored
Some systems show a low-bitrate viewing stream but archive the higher-bitrate main stream. Use the bitrate of the archived video. If audio is stored, add its bitrate; if different cameras or recording profiles are used, calculate each group separately and add the storage. Retention is based on what is truly saved, not just what appears in the mobile preview.
For a single camera clip or a general recording project, the Video Recording Storage Calculator is the closer match. For screen captures with a changing desktop scene, use the Screen Recording File Size Calculator.
Before buying storage
- Record or obtain the actual average bitrate for each archived camera stream.
- Write down cameras, daily hours, retention days, audio and expected event activity.
- Run continuous and reduced-recording scenarios, then allow room for operating overhead.
- Compare the recorder’s usable recording capacity with the result, not just the sum of raw drive labels.
- Confirm the achieved retention in the recorder after a representative recording period.
This method estimates storage, not footage quality, evidentiary suitability, privacy compliance or guaranteed retention during an unusually busy scene. Check those requirements separately.