Security Camera Storage Calculator (2026): How Much Storage You Actually Need

Quick Answer: Storage need comes down to one formula: GB = Bitrate (Mbps) x 10.8 x Days x Cameras. A single 4K camera recording continuously in H.265 (6-8 Mbps) uses roughly 65-86GB a day, per Reolink’s published bitrate table, while the same camera on H.265+ smart encoding drops to 32-54GB a day. For a typical 4-camera 4K system with 30-day retention, that works out to somewhere between 8TB and 10.5TB of storage — enough to size an NVR hard drive or plan a microSD budget correctly before you buy, instead of finding out three weeks in that footage is already overwriting itself.

Most buyers size a security system around cameras and never think about the hard drive or SD card until footage starts disappearing early. The math isn’t complicated once you have the right inputs — resolution, codec, camera count, and how many days of history you actually want — but the marketing pages for most NVR kits and cameras don’t spell it out. Here’s the formula, the real bitrate numbers behind it, and where the estimate quietly breaks down.

Storage per camera, by resolution and codec

These figures assume continuous 24/7 recording at a typical 15-30fps — the worst case for storage, and the number to plan against if a drive needs to last a set number of days without attention. Motion-triggered recording can use less, but often less than buyers expect (more on that below).

The formula, worked through

Reolink publishes the underlying math on its own CCTV storage-calculation page: Storage (GB) = Bitrate (Kbps) x 1000/8 x 3600 x 24 x Cameras x Days / 1,000,000,000. Simplified to megabits and rounded, that’s:

Storage (GB) = Bitrate (Mbps) x 10.8 x Days x Cameras

A worked example for a common setup — 4 cameras, 4K resolution, H.265 encoding, 30-day retention:

• Low end (6 Mbps): 4 cameras x 6 Mbps x 30 days x 10.8 = 7,776GB (≈7.8TB)
• High end (8 Mbps): 4 cameras x 8 Mbps x 30 days x 10.8 = 10,368GB (≈10.4TB)

That’s why most 4-camera 4K NVR kits ship with an 8TB-10TB drive rather than a round number picked arbitrarily — it’s sized against continuous H.265 recording at roughly a month of retention.

Sizing storage for a multi-camera rental property or small office? A free Amazon Business account unlocks quantity discounts and tax-exempt purchasing when you’re buying an upgraded NVR drive or a batch of endurance microSD cards at once.

Why motion-triggered recording saves less than you’d think

The instinct is that switching from continuous to motion-triggered recording cuts storage dramatically — and it can, in a quiet spot. But Lorex’s own hard-drive calculator notes that with motion recording enabled, a typical camera logs about 120 triggered events of 30 seconds each per hour, which adds up to a full 60 minutes of saved footage per hour of real time. In other words, a camera pointed at a busy sidewalk, a driveway with regular car and foot traffic, or a shared hallway can end up recording almost as much motion-triggered footage as it would continuously. The setting saves real space mainly in genuinely low-traffic spots — a back fence line, a rarely-used side gate — not the entryway or driveway most buyers actually want covered.

Cutting the number down: codec and drive choices that matter

• H.265 over H.264 is the single biggest lever. Lorex states H.265 encoding reduces data size by 25-50% compared to H.264 at equivalent visual quality, and the bitrate table above shows exactly that — a 4K H.264 stream at 12-16 Mbps drops to 6-8 Mbps on H.265. Most systems sold since roughly 2022 default to H.265 already; confirm an older NVR or camera isn’t still set to H.264 before sizing a drive.
• Smart/AI encoding (H.265+, Smart Codec) is the second lever. These modes detect static background and drop bitrate when nothing’s moving, cutting the 4K H.265 range down to 32-54GB a day per camera — close to half of straight H.265, without giving up continuous recording.
• Surveillance-rated drives cost more per terabyte, and that’s the point. Purpose-built drives like WD Purple Pro and Seagate SkyHawk AI run roughly $25-35 per terabyte, per PVRBlog’s tracked pricing — noticeably more than a generic desktop hard drive, because they’re firmware-tuned for the 24/7, write-heavy workload an NVR actually creates rather than the occasional read/write pattern of a normal PC drive.
• For single-camera or SD-card-based setups, endurance rating matters more than raw capacity. A camera writing to a microSD card instead of an NVR needs a card built for continuous overwriting, not just a large one — see our best SD card for security cameras picks for endurance-rated options sized against exactly this kind of continuous-loop math.

The bottom line

Storage sizing comes down to four inputs you already know before buying anything: resolution, codec, camera count, and how many days of history you want on hand. Run those through GB = Bitrate (Mbps) x 10.8 x Days x Cameras, lean on H.265 or smart encoding wherever the camera supports it, and budget $25-35 per terabyte for a drive actually rated for continuous surveillance writes rather than a generic desktop one. Still deciding between cloud and local storage in the first place? Our cloud vs local storage guide walks through that tradeoff, and if the plan is a single camera on a microSD card rather than a full NVR, our best security camera with local storage picks cover which models actually take a card.