Sizu Riatto
Every Angle · Chapter 10

Storage: Days on the Drive

Video is a stream of megabits every second. Multiply by the seconds in a day and divide by eight, and you know how long the recorder remembers.

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Opens on the book's house and plot. Change any number to your own and press Calculate.

The recorder

Power over Ethernet (optional)

Enter the bitrate, the cameras and the drive, then press Calculate.

The formula

  • GB a day = Mbps × 3,600 × hours ÷ 8 ÷ 1,000 (8 bits to a byte, 1,000 MB to a GB)
  • Days on the drive = the drive's GB ÷ (GB a day × cameras)
  • PoE power = watts a camera × cameras; kWh a year = W × 24 × 365 ÷ 1,000; cost = kWh × the price
The book's worked example, Chapter 10. H.265 at 2 Mbps is 21.6 GB a day a camera, 108 GB for five, so a 2 TB drive holds 18.5 days; H.264 at 4 Mbps holds 9.3 days. PoE at 5 W a camera is 25 W, 219 kWh a year, about 39.42 at 0.18 a kWh, plus the recorder's own draw (read its label).
Check it. After a week, look up how much of the drive the recorder says is used: divide by seven and by the cameras, and compare with GB a day.

Honest limits. Bitrates are averages: a busy street, rain and night noise push them up, and motion-only recording brings them down. Keep only what you need, for as long as you need it: in many places that is the law, not just good manners. The book's house was worked out on paper from published figures, not surveyed by us: measure your own, and walk your own plot at night. Prices are illustrative US prices from November 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.

These calculators go with Every Angle (Make It Add Up, Book 2), where every number on this page is worked by hand.