Idle power consumption is hard to compare because peripherals, configuration and firmware have enormous sway.

However, painting with broad brushes, Sandy Bridge has modern power management and idles comparably to newer CPUs (a lot better than some modern ones even).

I actually measured the whole system. With motherboard, HDD, SSD and RAM it idled at 30W. CPU took only 7w from all of that.

How did you measure CPU draw?

(Not the same commenter) HWInfo64 can report your CPU power consumption. Some digital power supplies can also give power for specific parts, like corsair iCue compatible PSU's

Reported by the motherboard's current sensor.

Is that accurate?

Well if you count expected power consumption of each component and limited efficiency of the power supply, plus reports of people idling their 3470 based machines at 12w (full system) yeah, good enough. I mean what is your point? The 35W idle for Ivy Bridge CPU only is a ridiculous claim, that should be retracted IMO.

CPU and mobo sensors are accurate enough for casual measurements and conversations like this.

The numbers I cited earlier were reported by the CPU's package power sensors which were in turn read by LibreHardwareMonitor.