CCTV Storage Calculator (NVR / DVR Hard Drive Size and Recording Days)
Hard-drive capacity for a security camera system — cameras, resolution and codec (H.264, H.265, smart codecs), frame rate, scene activity, recording hours, motion share and retention days — or how many days your drives hold, with RAID drive counts, NVR bandwidth and retention tables.
How it works
Bitrate = preset (at 15 fps) × fps ÷ 15 × scene factor × smart-codec factor · Bytes per camera per day = bitrate (Mbps) × 10⁶ ÷ 8 × recording seconds × motion share (+ sub-stream) · Storage = per day × cameras × retention days · Days = capacity ÷ per day · 1 Mbps continuous ≈ 10.8 GB a day
Video storage is bitrate times time. A camera streaming at 4 Mbps writes half a megabyte every second — about 43 GB a day — and a modest eight-camera system can fill terabytes in a month. Bitrate is what you control: H.265 roughly halves it against H.264 at the same quality, smart codecs (H.264+, H.265+, Zipstream) cut static scenes by about another third, lower frame rates help roughly in proportion, and motion-triggered or scheduled recording can cut storage by two thirds or more in quiet places. Scene activity matters too: rain, trees in the wind and night-time noise all push the bitrate up. Pick a resolution and codec preset or type the bitrate your NVR reports, set the frame rate, recording hours, motion share and retention, and the calculator gives the terabytes needed — or switch to “Days my drives hold” to see how long a given capacity lasts. Under More options you can add a second camera group (for example 4K outside and 1080p inside), record a sub-stream as well, choose the drive size and a RAID level, and set how much free space to keep. Results include the drive count, NVR bandwidth and port, the yearly write load against surveillance-drive ratings, and tables of retention by drive size and storage by retention period.
Worked example
Eight 4 MP H.265 cameras at 15 fps recording continuously for 30 days: 3 Mbps each is 3 × 10⁶ ÷ 8 × 86,400 s = 32.4 GB per camera per day, 259.2 GB a day for the system and 7.8 TB (7.1 TiB) for 30 days. Keeping 10% free, that needs 8.64 TB, so two 8 TB surveillance drives (about 61.7 days of footage) — or three in RAID 5 for the same space with a drive’s worth of protection. A single 8 TB drive alone would hold about 30.9 days.
Frequently asked questions
Why does the vendor’s calculator give a different number?
Different bitrate assumptions (VBR averages vs CBR peaks, scene complexity, quality setting) and TB vs TiB. Use your NVR’s live bitrate readout with the Custom option for the most accurate figure.
How much does motion recording save?
In a home or an after-hours office, typically 60–80% of storage; in a busy shop, very little. Many systems record a low-resolution sub-stream continuously and the main stream only on motion — set the motion share and the sub-stream bitrate to model that.
How many days does a 1 TB or 4 TB drive hold?
Divide the capacity by the daily total. Four 1080p H.265 cameras at about 2 Mbps write 4 × 21.6 = 86.4 GB a day continuously, so 1 TB lasts about 11.6 days and 4 TB about 46 days. Switch to “Days my drives hold” to work it out for your setup.
H.265 or H.264 for security cameras?
H.265 needs about half the storage for the same picture quality, so the same drive keeps roughly twice as many days. Check that the NVR, the viewing app and any VMS support it; smart variants (H.265+) save more on quiet scenes.
Do I need RAID for an NVR?
Not for a small home system, but on larger or business systems RAID 5 or 6 keeps recording when a drive fails and protects the footage you already have. RAID 5 costs one extra drive, RAID 6 two, and mirroring (RAID 1/10) doubles the drive count.
Which hard drives should I use?
Surveillance-rated drives (for example WD Purple or Seagate SkyHawk) are built for 24/7 writing from many streams and are usually rated for about 180 TB of writes a year. The calculator shows your yearly write load so you can check it against the rating.
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This calculator is for educational purposes. Double-check important results before acting on them.