What are the dimensions of electric field in SI unit?

Answer 1

It's simply Volts per meter or V/m. Add the usual prefixes such as n,m,k,M,G as appropriate, just like with other SI units.

A good ordinary electrical insulator, such as the PVC on an electrical cable can withstand hundreds of kV/m or put another way, it isolates hundreds of V/mm of thickness and can safely keep its isolation strength for 30 to 50 years of continuous use inside the walls of your home. The insulators used inside compact electronics capacitors sustain even larger field strengths (they are much thinner to increase the electrical capacity), but don't guarantee the ability to safely sustain and isolate those field strengths for half a century of continuous use.

In open air a 100kV high voltage power line on top of 10 meter high poles would create a 10kV/m open air electrical field between itself and the ground below. Those are just some easy to work with numbers, real world power lines are larger or smaller than that.

Answer 2

The dimensions of the electric field in SI units are N/C (newtons per coulomb) or V/m (volts per meter). The electric field represents the force experienced by a unit positive charge at a given point in space.