I thought it would be a good academic exercise for us to do the calculation:

Let's imaging a notional conductor, a cylindrical piece of wire.

Its cross-sectional area is A, the length is d and there are n charge carriers, e, moving at velocity v.

Therefore the total mobile charge, Q, in the cable is given by Adne

Time, t, for this charge to move along the conductor = d/v

Since current, I, = Q/t we can substitute for the above:

I = Adne / d/v = Avne

So v = I / Ane

Now i need some numbers for my notional copper wire including - number of charge carriers etc...

Who would like to take up the baton...