NVR Storage Calculator: How Much Hard Drive Do You Need?
Enter your setup below to estimate the hard drive size your security system needs. Figures are based on H.265 (HEVC) compression, the standard on most modern NVRs.
These are estimates. Real usage varies with scene complexity, motion frequency, frame rate, and your camera’s bitrate settings — a busy street uses far more than a quiet backyard. Always size up: pick the next drive size above your estimate so you don’t run short. Motion-only is modeled at roughly 8 hours of recording per day; your actual mileage depends on how much movement your cameras see.
Source: Guard Source HQ — guardsourcehq.com/nvr-storage-calculator. Free to cite with attribution and a link back.
How to Use This Tool
This calculator is for homeowners and installers sizing a hard drive for an NVR or DVR before they buy. You’ll need four things: how many cameras you’re running, their resolution (2MP/1080p up to 8MP/4K), whether they record continuously or only on motion, and how many days of footage you want to keep.
Enter your camera count, pick the resolution that matches your cameras, choose your recording mode, and set your retention in days. The result updates instantly, showing the estimated storage in terabytes and a recommended surveillance-rated drive. Treat that number as a floor, not a ceiling — real footage varies with how much your cameras see, so size up to the next drive tier.
When This Tool Is Most Useful
This calculator is most useful when you’re:
- Planning a new NVR or security camera installation and want to buy the right drive the first time
- Upgrading or replacing a hard drive that keeps filling up before your retention window is over
- Deciding how many days of recording retention you can realistically keep on a given drive
- Comparing storage requirements across resolutions or camera counts before you spend money
Example Calculation
Say you have 6 cameras at 4MP, recording motion-only, and you want to keep 30 days of footage. At 4MP the calculator uses a 4 Mbps bitrate per camera, and motion-only is modeled at about 8 hours of recording per day.
- Per camera per day: 4 Mbps × 8 hours ≈ 14.4 GB
- All 6 cameras per day: ≈ 86 GB
- Over 30 days: ≈ 2.6 TB
The tool rounds this up to a recommended 4 TB surveillance drive, the next size above the estimate.
Why 4 TB and not 3? The 2.6 TB figure assumes an average residential scene, but real motion is lumpy — a delivery, a dog, wind-blown trees — and busy days write far more than quiet ones. The next tier up absorbs those spikes and leaves the 15–20% free space a drive needs to run reliably, so you’re not replacing it in six months. Step up to a 6–8 TB drive if you record 24/7 instead of on motion, run cameras at 4K, want more than 30 days of retention, or plan to add cameras later. If your setup consistently lands above 8 TB, it’s usually time for an NVR with two drive bays or a NAS.
Common Mistakes
- Using the wrong bitrate. Entering 1080p when your cameras are actually 4K — or leaving them on H.264 instead of H.265 — throws the estimate off by 2× or more. Check your camera’s real resolution and codec first.
- Forgetting frame rate. This tool assumes a typical 15 fps. A camera cranked to 30 fps for license-plate capture uses roughly double, so give it extra headroom.
- Sizing for motion but recording 24/7. Motion-only assumes the scene sits still most of the day. A camera facing a busy street or road records far more, closer to continuous.
- Leaving no headroom. Buying a drive that exactly matches the estimate leaves nothing for busy days. Size up one tier and keep about 15–20% free.
- Using a desktop hard drive. Desktop drives (WD Blue, Seagate Barracuda) aren’t built for constant recording and often fail in 6–18 months. Use a surveillance-rated drive like WD Purple or Seagate SkyHawk.
Accuracy & Assumptions
This calculator gives an estimate based on the camera count, resolution, recording mode, and retention you enter, using H.265 compression as the baseline. Real-world storage use can run higher or lower than the figure shown, depending on:
- Variable bitrate (VBR) — most cameras raise and lower their data rate with scene activity rather than holding a fixed rate
- Scene motion — a busy street or a wind-blown tree line writes far more than a quiet interior
- Compression codec — H.264 uses roughly double the storage of H.265 for the same footage
- Camera firmware and encoding settings — defaults vary between brands and models
- Motion-only recording — the savings depend entirely on how often your cameras actually trigger
Always leave additional storage capacity for future cameras and unexpected recording needs. Sizing up one drive tier is the simplest way to stay ahead of the variables above.
Next Steps
Your drive size is only half the plan. Next, calculate your camera bandwidth to confirm your network and NVR can handle the data load, and if you’re running PoE cameras, check your PoE power budget so the switch can power them all. For the reasoning behind the numbers, read the full NVR storage sizing guide. Already recording but the drive isn’t cooperating? See NVR says “no hard disk” or won’t record.
Related Resources
Related calculators & charts
- NVR Storage Size Chart — drive sizes at a glance by camera count and resolution
- Camera Bitrate & Bandwidth Chart — how much network throughput your cameras use
- PoE Budget Calculator — make sure your switch can power every camera
Related guides
- How Much NVR Storage Do You Need? — the full sizing guide behind this tool
- NVR Says “No Hard Disk” or Won’t Record — fix a drive the NVR won’t use
Browse all free security camera & NVR tools.
Frequently Asked Questions
How much hard drive storage do I need for my NVR?
As a rough guide, a 4-camera 4MP system recording continuously for two weeks needs somewhere around 2 to 4 TB, while motion-only recording can bring that down to about 1 TB. The exact figure depends heavily on resolution and frame rate, so use the calculator above with your real camera count and retention target for a number you can buy against.
Does continuous recording use more storage than motion detection?
Yes, significantly. Continuous 24/7 recording writes footage every second regardless of activity, while motion-only recording stores clips only when something moves. For a typically quiet location, motion recording can use a fraction of the storage, though it risks missing events during the brief moment the camera takes to trigger.
What size hard drive can an NVR support?
Most modern NVRs support drives up to 8 to 16 TB per bay, and many have two or more bays, but always check your specific model maximum. Use a surveillance-rated drive such as WD Purple or Seagate SkyHawk rather than a desktop drive, because they are built for the constant write load of 24/7 recording.
How long will a 4TB drive record on a security system?
A 4 TB surveillance drive holds roughly two to four weeks of continuous footage for a typical four-camera 4MP system, and a month or more on motion-only recording. More cameras, higher resolution, or 30 fps will shorten that. Run your exact setup through the calculator above for a firm number.
Do I really need a surveillance-rated hard drive?
Yes. Surveillance drives such as WD Purple and Seagate SkyHawk are built for the constant 24/7 writing a camera system does. Desktop drives often fail within 6 to 18 months under that load, and SSDs wear out even faster, so the small price difference is worth it.
Does 4K really use twice the storage of 1080p?
Roughly, yes. For the same frame rate and codec, 4K (8MP) records about double the data of 1080p (2MP). H.265 compression and motion recording keep that manageable, but plan for the higher figure when you choose a drive.
How much storage do 8 cameras need?
On motion recording with H.265, eight 1080p cameras need around 3 TB for 30 days, while eight 4K cameras climb to roughly 10 to 12 TB. At that point one drive bay may not be enough, so consider an NVR with two bays or a NAS. Use the calculator for your specific resolution and retention.
About Guard Source HQ — Guard Source HQ is built on 30 years in the construction trades — real-world experience installing equipment, keeping systems running, and protecting them from the elements. Every guide here follows the same rule: practical, field-tested advice on security cameras and the networks behind them, without the scare tactics or the hard sell.
Guard Source HQ exists to give homeowners practical, experience-based troubleshooting and clear educational resources — tools and guides that help you plan, install, and maintain your own security setup with confidence, and make an informed decision before you buy.
July 2026
- Expanded instructions and how-to guidance
- Added a worked example and calculator assumptions
- Updated and expanded the FAQ
- Improved storage recommendations
Last updated: July 2, 2026