How many days will a 128GB card actually hold? Our security camera storage calculator answers that question for Australian homes: pick your cameras, resolution and recording mode, and it works out how much footage you record each day, how long your card or NVR lasts, and what size storage you need for 7, 14 or 30 days of retention.
Storage is the question every no-subscription buyer hits next. A camera that records around the clock fills a card six times faster than one that only records motion — and that single difference matters more than the card size. This security camera storage calculator makes the maths visible, so you buy the right card the first time instead of discovering it overwrote last week’s footage.
How the storage maths works
Every result on this page uses one printed formula, so you can check it by hand:
GB per day = bitrate (Mbps) × seconds recorded per day ÷ 8 ÷ 1000
Days retained = usable storage (GB × 0.93 formatting reserve) ÷ GB per day
Multi-camera setups add the GB per day of every camera together before dividing. The 0.93 reserve accounts for formatting overhead — a card labelled 128GB holds about 119GB of footage. That is the whole method this security camera storage calculator uses, with no hidden assumptions. Bitrate presets below are typical H.265 event-recording averages and are editable: your actual bitrate varies with scene motion, night infrared and each brand’s variable bitrate, so treat every result as an estimate, not a manufacturer specification.
Card size needed for your target retention: 7 days — · 14 days — · 30 days —
Estimates only. Actual bitrate varies with scene motion, night infrared and brand variable bitrate. Re-check the card size against your camera’s own storage guidance before you buy.
Three worked examples
One 2K camera, recording 24/7, on a 128GB card: 2 Mbps × 86,400 seconds ÷ 8 ÷ 1000 = 21.6 GB per day. Usable storage is 128 × 0.93 = 119.04 GB, so the card holds 119.04 ÷ 21.6 = 5.5 days.
The same camera, motion-only at 4 hours of recording a day: 2 × 14,400 ÷ 8 ÷ 1000 = 3.6 GB per day, so the same card holds 119.04 ÷ 3.6 = 33.1 days. That six-fold swing is the single biggest variable in home camera storage — and the reason motion-only recording suits most front doors.
Four 1080p cameras on a 2TB NVR, recording 24/7: 4 × 10.8 = 43.2 GB per day. Usable storage is 2000 × 0.93 = 1,860 GB, so retention is 1,860 ÷ 43.2 = 43.1 days. A 30-day target needs 43.2 × 30 ÷ 0.93 = 1,394 GB, about 1.4TB minimum.
What this means for your setup
If your result is under a week, you have three honest levers: switch to motion-only recording, drop a resolution step, or buy a bigger card. Run your own numbers through the security camera storage calculator before buying a bigger card — a mode change is free, and often buys more days than the next card size up. If your result is over a month, you are probably overpaying for storage you will never watch — footage older than a fortnight rarely matters unless an incident was reported late. For the money side of the same decision, see our Security Camera Subscription Cost Calculator, which compares what each brand’s cloud plan adds over 1, 3 or 5 years.
Storage choice also interacts with the camera itself: our security camera storage options guide explains microSD, HomeBase and NVR trade-offs; our best security camera without subscription roundup picks the cameras that record locally with no monthly fee; and our best home security camera flagship covers the subscription cameras whose footage this calculator sizes.
Frequently asked questions
How many days will a 128GB card last in a security camera?
It depends on resolution and recording mode. A single 2K camera recording 24/7 fills a 128GB card in about 5.5 days, while the same camera recording motion-only for 4 hours a day lasts about 33.1 days. Use the security camera storage calculator above with your own settings for an exact estimate.
Is H.265 really half the storage of H.264?
Not exactly half, but close enough to matter: at like quality, H.264 needs roughly 1.8 times the bitrate of H.265, so the same card holds roughly 1.8 times less footage. Most cameras sold in Australia since 2023 default to H.265 — check your camera’s settings if your card fills faster than this calculator predicts.
Why does my card hold less than its labelled size?
Formatting overhead. A card labelled 128GB exposes about 119GB of usable space, which is why this calculator multiplies labelled size by 0.93 before dividing. The same reserve applies to NVR hard drives.
Does motion-only recording miss events?
It can, if the detection zone or sensitivity is set too narrow — a person crossing the far edge of frame may not trigger a clip. Aim the camera at the approach path, not just the door, and test it by walking the route yourself before relying on motion-only mode.
How much storage do I need for 30 days?
Multiply your GB per day by 30 and divide by 0.93. Four 1080p cameras recording 24/7 need about 1.4TB; a single 2K motion-only camera needs under 120GB. The calculator above prints the 7, 14 and 30-day sizes for your exact setup.
Storage estimates checked 24 October 2026. Bitrate presets are typical H.265 averages, not manufacturer specifications, and are re-checked quarterly.