Sizing an NVR From Megabytes per Hour
Every surveillance quote comes down to the same arithmetic. The cameras tell you how many megabytes they write in an hour, the retention clause tells you how many hours you have to keep, and the recorder you are specifying is sold in terabytes. Multiply, convert, add headroom — and only then do you know whether the job needs a two-bay box or a full drive array.
This page handles the conversion in the middle. Work out the site's total megabytes across the retention window, drop it in, and read the terabyte figure the bill of materials actually needs.
TB = MB ÷ 1 000 000. Worked example: a camera writing 500 MB per hour around the clock for 30 days produces 500 × 24 × 30 = 360 000 MB, which is 0.36 TB of recording for that one channel.The Three Numbers Behind Every Storage Quote
What one camera writes per hour
How long you must keep it
What the recorder can hold
Working a Recording Estimate Through the Converter
Total the site's megabytes over the retention window
Add up the megabytes per hour across every channel, then multiply by the retention hours — 720 for a 30-day continuous spec. Enter that total in the left field, which is already set to MB. A comma or a dot both work as the decimal mark and spaces are ignored, so a figure pasted from a spreadsheet drops straight in.
Read the terabyte requirement
The right-hand field updates as you type. Seven- and eight-digit megabyte totals are displayed with a space between thousands, so a multi-camera site total stays readable while you check you have not slipped a zero.
Copy the figure into the quote
The copy button on each field puts the bare number on the clipboard — no unit, no spacing — ready for the storage line of a bill of materials or a survey document. Ctrl+C inside a field does the same.
Reverse it to test a recorder you already have
Both fields are editable, so typing a drive or array size on the right returns the megabytes it holds; divide that by the site's hourly rate and you have the days of retention it can honestly promise. The swap button flips the pair, and the searchable dropdowns reach GB for a single channel or PB for an estate-wide rollout.
Camera Resolution, Hourly Volume and 30-Day Retention
One camera, recording continuously, for a 30-day window of 720 hours. Rates are representative mid-range figures for a moderately busy scene; your own cameras will land above or below depending on frame rate, scene detail and night-time noise.
| Camera and codec | MB per hour | MB over 30 days | TB over 30 days |
|---|---|---|---|
| 1080p (2 MP), H.264 | 1 800 MB | 1 296 000 MB | 1.296 TB |
| 1080p (2 MP), H.265 | 900 MB | 648 000 MB | 0.648 TB |
| 4 MP, H.264 | 3 600 MB | 2 592 000 MB | 2.592 TB |
| 4 MP, H.265 | 1 800 MB | 1 296 000 MB | 1.296 TB |
| 4K (8 MP), H.264 | 7 200 MB | 5 184 000 MB | 5.184 TB |
| 4K (8 MP), H.265 | 3 600 MB | 2 592 000 MB | 2.592 TB |
Scale a row and the shape of the job appears fast. Sixteen 4 MP channels on the newer codec is 16 × 1 800 = 28 800 MB an hour, or 20 736 000 MB across 720 hours — 20.736 TB before a single percent of headroom. Run the same site on the older codec and the requirement doubles to over 41 TB, which is the difference between a four-bay recorder and a rack unit.
Estimate forwards, verify backwards
Enter a site total on the left to size a recorder, or a drive capacity on the right to check what an existing box can actually retain. Both fields are live, so the sanity check costs one keystroke.
Numbers a quote can accept unedited
Copying a result gives you the raw value with no unit and no separators, which is what a costing sheet or a survey form wants before it applies its own formatting.
Single channel to whole estate in one list
The searchable unit dropdowns on both sides carry GB and PB alongside MB and TB, covering a one-camera lock-up and a multi-site rollout without leaving the page.
Legible at seven-digit megabyte totals
Thousands are spaced apart and very large values switch to exponent form, so a year-long retention figure is readable instead of an unbroken run of digits you have to count.
Surveillance Storage Questions
How much does moving from H.264 to H.265 really save on a 30-day archive?
Roughly half, for comparable picture quality — the table above shows a 4 MP channel dropping from 2.592 TB to 1.296 TB across the same 30 days. The saving is real but conditional. Older client software and some browser-based viewing struggle with the newer codec, decoding load on a viewing workstation rises, and a noisy infrared night scene erodes the advantage because sensor grain is expensive to compress whatever the codec. Test with the actual cameras on the actual site before you buy drives against the optimistic number.
Will motion-triggered recording cut storage as much as the sales sheet suggests?
Only in proportion to how quiet the scene genuinely is. A car park with activity 15% of the time takes a 4 MP channel from 1.296 TB down to about 0.19 TB over 30 days, which is a transformative saving. But pre-event and post-event buffers extend every clip, wind in foliage and headlights sweeping a wall trigger recordings nobody wanted, and many specifications insist on continuous recording so that footage is defensible with no gaps to explain. A common compromise is continuous at low frame rate with a high-quality stream on motion.
How much capacity should I buy on top of the converted retention figure?
Plan on a comfortable margin rather than a precise fit. The recorder claims some space for its database and index, daytime scenes run hotter than the datasheet average, and any redundancy scheme costs capacity outright — a parity-protected set gives up one drive's worth of space, and a mirrored pair gives up half. Eight 4 TB drives with single parity leave 28 TB before formatting, which covers the sixteen-camera example above with sensible room to spare. Adding ten to twenty percent on top of that is normal practice, and it is cheaper than explaining a shortfall after the recorder starts overwriting early.
Why is the recorder filling faster than my estimate in the first week?
Because cameras adapt their output to the scene, and datasheet figures describe a calm one. Rain, moving branches, a busy shop floor or a crowd all raise the data rate; so does infrared night mode, whose grain the encoder has to spend bits describing. A channel quoted at 1 800 MB an hour can run half again as high through a stormy week. If the retention promise is contractual, cap the per-channel rate in the camera settings rather than hoping the average holds, and re-measure real hourly volumes after the first fortnight.
What is the quickest way to quote a mixed site with several camera types?
Group by camera type, get to a single site-wide megabytes-per-hour figure, and convert once at the end. Twelve 4 MP channels at 1 800 MB an hour give 21 600 MB; four 4K channels at 3 600 MB an hour add 14 400 MB; the site runs at 36 000 MB an hour. Across 720 hours that is 25 920 000 MB, or 25.92 TB. Converting once at the end rather than per camera keeps rounding errors out and leaves you one number to apply headroom to.
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