PoE Budget Calculator

To download and print without a watermark, please log in and request approval.

Log in

This PoE budget calculator tells you whether a Power over Ethernet switch can actually power everything you plan to plug into it. It adds up the power drawn by each camera, access point, IP phone or reader, includes the loss in the cable, and compares the total with both the switch's overall PoE budget and the per-port limit of the PoE standard the switch supports.

It is meant for CCTV and network designers choosing a switch, installers checking an existing cabinet before adding cameras, and anyone troubleshooting cameras that reboot at night when infrared LEDs and heaters switch on. The result shows the load as a percentage of the budget, flags devices that exceed their port class, and recommends a budget with a safety margin.

What you enter

  • The switch's total PoE budget in watts and its number of PoE ports.
  • The PoE standard per port: 802.3af, 802.3at (PoE+) or 802.3bt.
  • Each device type with its maximum power from the data sheet, quantity, class, cable length and cable type.
  • A safety margin in percent.

Quick start

  1. Enter the switch budget and port details, or press Load demo to see a worked case.
  2. Add one row per device type with its maximum power.
  3. Check the budget bar and the per-device results for anything over limit.
  4. Save, export or print the result for your submittal.
Techubox

PoE Budget Calculator

Check a PoE switch's power budget, port count and per-port class limits, including cable loss, for cameras, APs, phones and readers.

FreeNo sign-upIEEE 802.3af / at / btCable loss included

1 · PoE switch

Calculate by?

Recommended budget = load × (1 + margin). 20% covers start-up surges, IR/heater peaks and ageing.

2 · Powered devices

One row per device type. Use the datasheet maximum power (IR on, heater on), not the typical figure. Each device uses one port.

Switch front panel

≤ 75% of port limit75–100%fault / over limitfree port

PoE budget

Per-device results

    📘 Worked example
    🎓 How to use this tool
    1. Enter the switch model, its total PoE budget in watts (from the datasheet, not the power-supply rating) and the number of PoE ports.
    2. Pick the port standard: 802.3af, 802.3at (PoE+), or 802.3bt Type 3 / Type 4. This sets the per-port limit.
    3. Add one row per device type. Choose a preset or type the device's maximum power from its datasheet, and set the quantity.
    4. Leave Class on Auto or set the class printed on the datasheet. A device that draws more than its class allows is flagged.
    5. Enter the cable length and cable type for each row. Cable loss is added to give the power the switch must supply.
    6. Choose Calculate by: device max power, or class allocation if your switch reserves power by class.
    7. Read the KPIs and verdict. Keep the load inside the green zone of the budget bar, then save, export or print the result.

    Tips & common mistakes

    • Use the camera's max power with IR LEDs and heater on. Night-time IR and cold-start heaters are where budgets fail.
    • The PoE budget is often far below the PSU rating: a "250 W" switch may only have 190 W for PoE. Check the datasheet.
    • Copper-clad aluminium (CCA) cable has about 1.6× the resistance of copper. It increases loss and is not standards-compliant for PoE.
    • A 60 W heater PTZ needs an 802.3bt Type 4 port (or a midspan/injector). It will not run on PoE+.
    • Over 100 m, use a PoE extender or a fibre link with a local PoE switch.

    Standards & assumptions

    IEEE 802.3af-2003, 802.3at-2009 and 802.3bt-2018 (now part of IEEE 802.3) PSE and PD class powers; ANSI/TIA-568 and ISO/IEC 11801 (100 m channel, 90 m permanent link). Cable loss is P = I²R at the minimum PSE voltage (44 V af, 50 V at/bt Type 3, 52 V bt Type 4), with conductor DC resistance at 20 °C of 9.38 Ω/100 m for 24 AWG (TIA maximum) and 7.33 Ω/100 m for 23 AWG (typical). 2-pair powering is assumed up to Class 4 and 4-pair for Classes 5–8. Per-pairset current limits of 350 / 600 / 600 / 960 mA are typical. Higher temperatures and bundled cables increase resistance. Device powers in the presets are typical; use your datasheet. The result is for guidance only and must be verified against the manufacturer's data and local code.

    Techubox Engineering Tools · techubox.com/tools

    Notes and limits

    • Typical per-port power at the switch: 802.3af 15.4 W, 802.3at 30 W, 802.3bt Type 3 60 W and Type 4 90 W. The power available at the device is lower because of cable loss.
    • Use the device's maximum power with IR and heater on, not the typical figure. Camera data sheets list both.
    • The switch's PoE budget is often lower than its power supply rating, and some switches reduce the budget at high temperature. Check the data sheet.
    • The Ethernet channel limit is 100 m. Long bundles in hot ceilings increase cable loss and heating, so keep a margin and use engineering judgment.

    Related guides on Techubox

    Scroll to Top