Skip to content
Calixo

PoE Cable Voltage Drop Calculator

Estimate voltage drop across a PoE/Ethernet cable run for a given wire gauge, current and length.

Inputs

e.g. a PoE+ device drawing ~0.3A at 48V (~15W).

Saved Scenarios

— select 2+ to compare

Voltage Drop (V)

3.08

Spark says

How it's calculated

Formula

Vdrop=2×I×Lengthft×Rper 1000ft1000V_{drop} = \dfrac{2 \times I \times Length_{ft} \times R_{per\ 1000ft}}{1000}
2 \times
— Accounts for both the outbound and return conductor

What is the PoE Cable Voltage Drop Calculator?

Voltage drop over a cable run is proportional to current, distance and the wire's resistance per unit length — for PoE runs, excessive drop can starve a camera or access point of the voltage it needs to power on reliably.

How to use it

  1. 1 Choose your cable's wire gauge.
  2. 2 Enter the current the powered device draws.
  3. 3 Enter the one-way cable length.

Worked examples

24 AWG, 0.3A, 200ft

About 3.08V dropped over the run.

Try it

Limitations

  • •Uses standard copper wire resistance tables at room temperature — actual resistance rises somewhat with temperature and varies slightly by manufacturer.

Frequently asked questions

How much voltage drop is too much for PoE?

Most PoE devices need a minimum input voltage (often ~37-42V for 48V nominal PoE) to function — as a rule of thumb, keep total drop under 10-15% of the source voltage.