In this work, we investigated a scalability of spin accumulation signal for various device sizes. We found that the spin accumulation signal is enhanced by shrinking Cu wire width and thickness. Moreover we estimate the signal to noise ratio (SNR) of a spin accumulation head structure by using the size dependence of spin accumulation signal. The SNR increases with reducing nonmagnetic wire width and thickness, which are corresponding to a track width and a gap width, respectively. And it has the maximum value around 2 ~ 3 Tbit/inch2 resolution. From these results, it has a possibility that spin accumulation effect is applicable to a new read head for high density hard disk drive.