Soumen Dutta, What exactly you mean? Why you want to mutiply by 5 to compare? compare with? In geometrical area of GCE, depends of your electrode, I used electrode with diameters 3, 5 and 6 mm2.

If you are referring to calculate electrode geometrical area, well: (pi)*(ratius)exp2, be care with units.

For ECSA. Actually if you keep in mind this data, and you want to compare several materials tested with the same electrode, does matter the geometrical area, is a commun factor for everyone. If you want mass activity, you must be know the mass in each experiment (this value is not the same usually).

Only normalized activities (current densities) can be compared!!! Depending on what you want to get out from your comparison, chose an appropriate definition. 

Reactions are happening on an atomic scale. Normalization to geometric area, to get current density (Jgeo), is ONLY useful if you compare macroscopic electrode that are microscopic perfectly flat(well polished). If it is not, one has to take roughness into account. For that purpose, activity definitions such as specific activity(Js) and TOF are used.

When working with nanoparticles, the geometric area cannot be measured by a ruler. Clearly they are rough on a macroscopic level.  For them, normal activity definitions are mass activity(Jm), specific activity(Js) and TOF.

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Jm= J / "mass of active material"

Js= J / EC surface Area (ECSA)

TOF= J / Number of EC active sites (NECAS)

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NECAS can be measured from a Hupd or CO stripping experiment if a Pt electrode is used. The measured charge (Q) is divided by the charge of the electron to result in NECAS.

ECSA = NECAS / NECAS* or Q/Q* . The NECAS* or Q*  are measured from a well-known macroscopic perfectly flat sample. Polycrystalline Platinum has ~210uC/cm^2.

Observe that:

Js=TOF / (Surface atoms / area unit)

Article Investigation of the Oxygen Reduction Activity on Silver – A...

yes i agree with Dr.Gustav Karl Henrik Wiberg statement.... only current density can be compared. Convert your current values (I) into current density (J) than you can compare with any system. thank you

I also agree with Dr.Gustav Karl Henrik Wiberg. But there are many other ways to determine the  surface area  of the electrode (ex., BET and oth.)

now when you are saying multiply by 5, i dont know why do you ned to. as far as for comparison purpose, as is suggested, we need to plot current density vs voltage. now people usually report current density in three ways- mass normalised, surface normalised. even in surface area normalised current density people normalize current obtined with-

1) geometrical surface of the electrode dipped in electrolyte

2) raw ecsa

also when you are  normalising with mass, the % of loading has to be absolutely taken care of. this you can confirm by ICP data. 

once you are done, it is also advisable to do CO adsorption experiment to confirm your ECSA calculation. for further enquiry you can read the electrochemical journals , there they explain in detils

all the best