Determine real bandwidth usage

[dobledosis]

Hi, i need to determine my real bandwidth usage in windows, but i find discrepancies when comparing different methods.

Cacti says im using 3Mbps I/O:

Net Limiter says aim using 2Mbps I/O

Resource monitor says im using 2Mbps I/O

Task manager says im using 3% of 100Mbps = 3Mbps I/O (I think so)

I attach an image with this methods in that order..

This differences increases and are more noticeable when bandwidth usage increases. Which method should i trust and why this differences?

Thank you!