Example Data Table
| Scenario | PoE Budget (W) | Ports | Devices | Typical Required (W) | Notes |
|---|---|---|---|---|---|
| Small site | 120 | 8 | 6 | 72 | Phones and one access point with spare capacity. |
| Mid project floor | 370 | 48 | 42 | 315 | Cameras, phones, and access points with reserve. |
| High-power devices | 740 | 48 | 30 | 690 | PTZ cameras and radios; verify per-port limits. |
Formula Used
The calculator estimates switch power draw by applying duty cycle, headroom, and efficiency to each device line item.
- UsableBudget(W) = SwitchBudget × (1 − Reserve%) × (1 − Derating%)
- Base(W) = DeviceW × Quantity
- Adjusted(W) = Base × Duty% × (1 + Headroom%)
- FromSwitch(W) = Adjusted ÷ Efficiency%
- Remaining(W) = UsableBudget − Σ FromSwitch
Per-port caps are checked against the selected standard; your hardware datasheet remains the final authority.
How to Use This Calculator
- Enter total PoE budget and port counts from your switch label.
- Select the PoE standard or set a custom per-port cap.
- Set reserve, derating, and efficiency to match site conditions.
- Add each device type with watts and quantity for the project.
- Click “Calculate Budget” to review remaining watts and ports.
- Download CSV or PDF to attach to planning documents.
PoE budgeting in temporary and permanent job sites
Power over Ethernet planning prevents surprise outages when cameras, access points, and controllers grow during a build. This calculator converts a device list into estimated switch load, then compares it to the usable budget after reserve and derating. The result helps teams decide whether one switch is enough or if a second unit, midspan injectors, or a higher budget model is needed. It also highlights when port counts, not watts, are the bottleneck, which is common on mixed CCTV and Wi-Fi deployments with many low-power endpoints.
Why reserve and derating change real capacity
Manufacturers publish a total PoE wattage, but field conditions often reduce what you can rely on. Reserve keeps capacity for peak draw, firmware changes, and future drops. Derating reflects heat, crowded racks, long cable runs, and supply variability. Using both values produces a conservative usable budget that better matches construction environments.
Device inputs that improve estimate accuracy
For each device type, use typical power draw from the datasheet, not the maximum marketing figure. Quantity should match the planned port map. Duty cycle models devices that idle part of the day, such as speakers or gates. Headroom adds a safety margin for cold starts, infrared LEDs, or radio boost modes.
Interpreting per-port limits and standards
Total watts are not the only constraint. A high budget switch can still fail if a single device exceeds the per-port cap for the chosen standard. The calculator flags those lines so you can choose a different standard, confirm the device class, or plan an injector. This keeps design aligned with port-level electrical limits.
Deliverables for procurement and commissioning
Use the CSV download to share device schedules with vendors and electricians, and the PDF report for submittals and closeout packages. During commissioning, compare measured draw to the estimate and adjust assumptions for future phases. Documenting remaining watts and free PoE ports supports clean change orders and avoids last-minute rewiring for coordinated handover to facility operations.
FAQs
1) What PoE budget should I enter?
Use the switch’s published total PoE wattage from its label or datasheet. If you stack switches, enter the budget for one unit at a time so the device list stays traceable during procurement and testing.
2) Should I use device maximum watts or typical watts?
Prefer typical draw measured during normal operation. Maximum draw can be rare and may oversize the design. Add headroom and reserve to cover peaks without making the estimate unnecessarily pessimistic.
3) Why does efficiency affect required power?
Not all input power becomes delivered PoE power. Converters and cabling introduce losses, so the switch can draw more than the devices receive. The efficiency setting models those losses in one simple adjustment.
4) What does duty cycle mean for PoE loads?
Duty cycle represents the percentage of time a device draws its typical wattage. For always-on devices, keep 100%. For intermittent equipment, use a lower value to estimate average load more realistically.
5) What if a device exceeds the per-port cap?
The calculator flags that line so you can select a higher standard, confirm the device requirements, or plan a midspan injector. Even with plenty of total watts, an over-cap device may not power reliably.
6) How do I use the exports on site?
Download CSV for quick sharing and edits in spreadsheets. Use the PDF during toolbox talks, commissioning, and handover packages. Keeping the same report format helps track changes across phases and contractors.