Electrical & Electronics
PoE Power Budget Calculator
Plan switch power and port capacity for PoE devices, with reserve and per-port checks.
Your inputs
Your results
- Total allocated power
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- Budget after reserve
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- Remaining power
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- Used ports
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- Remaining ports
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- Power reserve
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—Plan PoE power and port capacity together
Budget device power at the supplying switch, including cable losses. Compare total allocation, occupied ports and the per-port limit separately. This planner does not detect devices, negotiate power classes or measure consumption.
Step by step
- Enter the switch's usable power budget, port count, per-port limit and reserve percentage from its documentation.
- Add device groups with quantity and power allocated per device at the switch. Replace presets when documented requirements differ.
- Review remaining power, remaining ports and every warning. Keep reserve for the operating conditions you intend to support.
Settings and limits
- Device allocation
- Use worst-case switch-side requirements, including cable loss, rather than average power delivered to the device.
- Reserved capacity
- Reserve reduces available power, not the number of ports. Reported utilisation uses the full entered budget.
- Per-port limit
- The same limit applies to every device. Mixed port capabilities or shared hardware limits require separate checks.
Worked example
Enter the switch and device groups below. The allocation fits the reserved power budget and leaves spare ports.
Example input
Pbudget = 370 W; Nports = 24; Pport,max = 30 W
r = 10%
nA = 8; PA = 30 W
nB = 4; PB = 15.4 W| P / N | ≈ |
|---|---|
| Pused | 301.6 W |
| Preserve | 37 W |
| Pavailable | 333 W |
| Premaining | 31.4 W |
| Nused | 12 |
| Nremaining | 12 |
A higher-power device can exceed the per-port limit even when total remaining power is positive.
Questions and troubleshooting
Why does the plan fail with spare watts?
Check port count and individual device allocations. Passing the total-power check does not satisfy those other limits.
Are preset powers measurements?
No. They are planning allocations. Check the switch and device documentation for the actual negotiated requirements.
Does a passing result guarantee operation?
No. Verify device compatibility, power-supply or redundancy mode, cable losses and startup demand.