When to use: Use to calculate the total PoE power budget for switch selection and PSU sizing. Enter device groups with their count and PoE standard. The calculator determines typical and maximum watts, then sizes the required switch PSU accounting for power supply efficiency. Critical for IP camera, Wi-Fi AP, VoIP, and access control system designs.
This calculator determines the total Power over Ethernet budget required for a switch and sizes the necessary power supply unit based on device groups and their PoE standard. Network engineers use it during LAN design to select switches with sufficient PSU capacity before purchasing hardware for IP camera, VoIP, Wi-Fi AP, and access control deployments.
Each PoE-powered device (PD) draws a maximum wattage defined by its IEEE standard class. IEEE 802.3af (PoE) delivers up to 15.4 W at the switch port, 802.3at (PoE+) up to 30 W, 802.3bt Type 3 (PoE++) up to 60 W, and 802.3bt Type 4 up to 90 W. The total maximum PoE budget is the sum of all ports at their class maximums, representing the worst case where every port is fully loaded simultaneously.
The required PSU capacity is the total maximum PoE watts divided by the PSU efficiency (typically 85–90% for modern switching power supplies), because not all input power reaches the ports — some is lost as heat in the conversion stage. The calculator then selects the next standard PSU size above the required wattage.
IEEE 802.3af (2003) defined the original PoE standard at 15.4 W per port. IEEE 802.3at (2009, PoE+) raised the limit to 30 W, enabling dual-radio Wi-Fi APs and higher-power PTZ cameras. IEEE 802.3bt (2018, PoE++) defined Type 3 (60 W) for multi-radio 802.11ac Wave 2 and 802.11ax APs, and Type 4 (90 W) for high-power endpoints like thin clients and video phones. NEC Article 725 and NFPA 70 govern the wiring practices for low-voltage systems that carry PoE. TIA-942 references PoE power density for data center equipment planning.
Never size the PSU exactly to the calculated maximum PoE draw. Allow at least 20–30% headroom above calculated maximum to account for simultaneous worst-case loads, PSU aging (which reduces output capacity over time), and future device additions. Verify that the switch chassis itself supports the selected PSU wattage — many switches require specific PSU modules to enable PoE on all ports. For large deployments, consider distributing load across multiple switches rather than maximizing PoE budget on a single switch, which reduces blast radius from PSU failure. Cable quality matters: PoE at high wattages (802.3bt) causes more resistive heating, making Cat 6A preferable to Cat 5e for 60–90 W applications.
Add device groups corresponding to your project (IP cameras, Wi-Fi APs, IP phones, access control readers). For each group, enter the device count and select the applicable PoE standard — use the device's datasheet to confirm the class. Set the PSU efficiency to match your switch specifications (typically 85%). The calculator outputs typical draw, worst-case maximum draw, required PSU wattage after efficiency loss, and the recommended standard PSU size. Use the PSU size to specify the correct switch SKU or PSU module part number.
802.11ax (Wi-Fi 6) APs commonly require 802.3bt Type 3 (PoE++ 60 W) when using all radios, 2.5G uplinks, and IoT radios simultaneously. Check the vendor datasheet — many operate at 802.3at (30 W) with reduced radio power.
Yes. PoE switches negotiate power class with each PD using Link Layer Discovery Protocol (LLDP) or 802.3af classification. Each port delivers only what the connected device requests, so mixing standards is fully supported and does not waste budget.
The switch will either shut down lower-priority ports (if port priority is configured) or simply deny power to ports beyond budget. Cisco and similar vendors allow per-port priority settings so critical devices (servers, APs) are powered before less critical ones (desktop phones).
Cable resistance causes voltage drop over longer runs. At 802.3bt Type 4 (90 W), a 100 m Cat 5e run can drop voltage significantly, causing the device to receive less than 90 W. Use Cat 6A cable (lower resistance) for long runs delivering high-wattage PoE.
For mission-critical PoE devices (security cameras, door access readers), specifying a redundant PSU is strongly recommended. A single PSU failure on a PoE switch will drop all powered devices simultaneously, which is a life-safety concern for door access control systems.
Try our Enterprise IT Networks Studio
More calculators, simulators, and guides for this discipline.