CCTV Storage and PoE Budget Calculator
Terabytes, bit rate, drive count and switch power from camera count, resolution and retention period — plus the pixels per metre your lens actually delivers.
Calculator
From camera count, resolution and retention period to terabytes and a switch power budget.
Result
The calculation runs entirely in your browser; nothing you type is sent to our servers. Only if you press “Turn this into a quote request” is the result written to your browser’s session storage, so it can be carried into the quote form.
Worked example
Opened with its default case — Number of cameras: 16 · Resolution: 4 MP (2560×1440) · Compression: H.265 — 40–50% smaller than H.264 — the calculator returns the figures below. They are written out here so the output is readable without running JavaScript: in print, with scripts disabled, or by a search engine.
| Input | Value |
|---|---|
| Number of cameras | 16 |
| Resolution | 4 MP (2560×1440) |
| Compression | H.265 — 40–50% smaller than H.264 |
| Frame rate | 15 fps |
| Recording hours per day | 24 |
| Retention period (days) | 30 |
| Capacity of one drive (TB) | 8 |
| Maximum camera power (W) | 6.5 |
| Target distance (m) | 0 |
| Lens horizontal field of view (degrees) | 90 |
| Result | Value |
|---|---|
| Total bit rate | 44 Mbps |
| Data per day | 475.2 GB/day |
| Raw storage needed | 14.3 TB |
| Drives suggested | 3 × 8 TB |
| PoE budget | 104 W (switch: 130 W) |
Change any field above and the calculator recomputes; this table is the default case only.
How many terabytes does a CCTV system need?
Storage is set by bit rate, not by resolution. The formula is storage (GB) = bit rate (Mbps) × 3600 × hours/day × days × cameras ÷ 8 ÷ 1000. As a shortcut, 1 Mbps recorded continuously for 24 hours ≈ 10.8 GB/day. Worked example: 16 cameras, 4 MP, H.265 at 15 fps (mid-band ≈ 2.75 Mbps), 24 hours, 30 days → about 14 TB raw, or 16.4 TB with a 15% margin — three 8 TB surveillance drives. The same system at the top of the band (3 Mbps) needs 15.6 TB, and a busy scene at 4 Mbps needs 21 TB. That is why the bit-rate assumption matters as much as the answer. H.265 stores 40–50% less than H.264 at the same quality, and the gain grows with resolution. On the power side, the switch budget is built on maximum draw, not typical (IR at night is the peak), with a further 20–25% headroom.
The storage formula
Storage (GB) = bit rate (Mbps) × 3600 × hours/day × days × cameras ÷ 8 ÷ 1000
Drive makers sell decimal terabytes (1 TB = 1,000 GB) while the operating system and the NVR report binary units (TiB). A drive labelled 8 TB therefore shows as roughly 7.3 TiB in the system — about 9% less. Plan on 91% of the label as usable capacity; this is the single most common capacity surprise on a finished installation.
Realistic bit-rate bands
| Resolution | H.264 (Mbps) | H.265 (Mbps) | Horizontal pixels |
|---|---|---|---|
| 2 MP (1080p) | 3–4 | 1.5–2 | 1920 |
| 4 MP (2560×1440) | 5–6 | 2.5–3 | 2560 |
| 5 MP | 6–8 | 3–4 | 2592 |
| 8 MP (4K) | 12–14 | 6–7 | 3840 |
These are variable-bit-rate mid-points for a normally busy scene at 15 fps. A car park at night sits near the bottom; a production line with constant movement, or a scene with rain, foliage and headlights, sits at the top or above it. Smart codecs (the manufacturer names vary) can halve these again on static scenes — and give back almost nothing on busy ones, which is exactly when you need the capacity.
Two settings change the number more than the camera choice does. Frame rate: going from 15 to 25 fps does not multiply the bit rate by 1.67 — encoders exploit the similarity between consecutive frames, so the real factor is closer to 1.4. Recording mode: motion-triggered recording is only a saving if the scene is genuinely quiet. On a busy corridor the trigger fires most of the day and you get continuous recording with gaps in the evidence.
Pixels per metre, not megapixels
“8 MP so we will be able to read faces” is the most expensive mistake in camera specification. What decides whether a face is identifiable is pixels per metre at the target distance, and that depends on the lens as much as the sensor. Scene width = 2 × distance × tan(FOV ÷ 2); pixel density = horizontal pixels ÷ scene width.
| Pixel density | What it supports | Typical use |
|---|---|---|
| 25 px/m | Detection — something is there, and it is a person | Perimeter, wide yard overview |
| 63 px/m | Observation — behaviour and direction of travel | Aisles, loading bays |
| 125 px/m | Recognition — a person you already know | Staff entrances, workshop floor |
| 250 px/m | Identification — a stranger, from the footage alone | Tills, reception, cash handling |
| 500 px/m | Verification against a document or a still | Access control, high-value goods |
The levels come from EN 62676-4, the operational-requirement part of the video surveillance standard series; the 2025 revision adds the 500 px/m level. The standard text itself is not reproduced here — these are the figures used in practice for scoping. The calculator reports the density your lens and distance actually give you.
The practical consequence: a 4 MP camera on a 12 mm lens covering a till at 3 m beats an 8 MP camera on a 2.8 mm lens covering the whole shop floor, for the one job that matters in a dispute. Wide lenses buy coverage and spend pixels; narrow lenses do the opposite. Most sites need both, on separate cameras, rather than a compromise on every camera.
PoE budget and cabling
| Standard | Power at the port | Guaranteed at the camera | Typical use |
|---|---|---|---|
| 802.3af (PoE) | 15.4 W | 12.95 W | Fixed dome or bullet, IR included |
| 802.3at (PoE+) | 30 W | 25.5 W | PTZ, heater, long-range IR |
| 802.3bt Type 3 | 60 W | 51 W | Heated PTZ, multi-sensor housings |
The gap between the two power columns is cable loss, and it is why the port figure is always higher. Size the switch on the port side and check the camera datasheet on the device side.
Three cabling rules decide whether the installation works on the day: the 100 m limit on a copper run is the total from switch port to camera including patch leads, not just the horizontal cable; solid copper conductors are required, and copper-clad-aluminium sold as “CCA network cable” will not carry PoE reliably over distance; and the switch’s total power budget must exceed the sum of maximum camera draws, not the sum of typical ones. A 24-port switch with a 185 W budget will not run 24 cameras drawing 6.5 W each at night, because the sum is 156 W before you add the 20–25% margin.
How long to keep footage
Retention is a policy decision with a legal edge, and the legal edge differs by country: some jurisdictions set a maximum, some set a minimum for particular premises, and most require that the period be justified and documented under data-protection law. Because the answer is jurisdiction-specific, this calculator does not assume one — you enter the number of days your own policy or regulator requires and it sizes the storage for that.
What is universal is the arithmetic: retention scales storage linearly. Doubling from 30 to 60 days doubles the drive count, the drive cost and the rebuild time when a drive fails. If you need long retention on a few cameras and short retention on the rest, set the periods per camera group in the NVR rather than applying the longest one to everything.
What to send us for a quote
Send the calculator output plus three things and the quote comes back complete: the number of cameras by type (fixed dome, bullet, PTZ, multi-sensor), the longest cable run on site, and whether the recorder sits in a rack with existing UPS. We quote cameras, recorder, drives, PoE switch, cable and installation consumables as one line-by-line list, on one invoice, delivered to the site.
Frequently Asked Questions
How many TB do 16 cameras need for 30 days?
At 4 MP, H.265, 15 fps, recording continuously, roughly 14 TB raw or 16.4 TB with a 15% margin — three 8 TB surveillance drives. Change any one of codec, frame rate or scene activity and the answer moves by 30–50%, which is why the calculator asks for all of them.
Does H.265 really halve the storage?
Close to it at the same subjective quality, and the saving grows with resolution: the gain at 4K is larger than at 1080p. The trade is decoding load — verify that your recorder, and any client machine that will play back several streams at once, supports H.265 in hardware.
Why does my 8 TB drive show as 7.3 TB?
Because the label is decimal (8 × 10¹² bytes) and the operating system reports binary units (TiB, 2⁴⁰ bytes). Nothing is missing; the two scales differ by about 9%. Plan on 91% of the label.
Can I use ordinary desktop drives in an NVR?
They will work and then fail early. Surveillance-rated drives are specified for continuous sequential writing, for several drives vibrating in one chassis, and with firmware that gives up on a bad sector quickly instead of stalling the recording. The price difference is small against the cost of rebuilding an array.
How much PoE headroom should the switch have?
Size it on maximum camera draw, then add 20–25%. Maximum is the figure with IR illumination at full output, which is exactly when you need the system to stay up. A switch that browns out at 3 a.m. records nothing at 3 a.m.
Do you supply the whole system or only the cameras?
The whole list — cameras, recorder, surveillance drives, PoE switch, cable, connectors, cabinet and the small items that hold up an installation. One quote, one invoice, delivered to site. Send the calculator result and the site details and it comes back within one business day.
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