Many EHL (elastohydrodynamic lubrication) experiments have been performed with the regard to measuring the film thickness variations according to contact conditions, such as contact load, sliding-rolling ratio, contact accelerations for the verification purpose of lubricant characteristics. The measured images of film thickness by the interferometry system are easily converted into film thickness values even both in nanometer scale and resolution with the help of image processing technology. However, only the measurement of the EHL film thickness is not enough to verify the lubricant characteristics under the various contact conditions, because the lubricant is under very high contact pressures above 500MPa, where the lubricant is suddenly solidified and is no longer considered as a fluid itself. In this work, the EHL fluid film pressures are computed from the measured interferometric image of contact film thickness ranging from 10nm to several hundred nano meter, which should be taken with nano-scale resolution. The image processing technique makes it possible to convert the measured film thickness into contact fluid film pressures if the contact geometry and material properties are known. Without the nano-scale resolution for the measured film thickness, the converting computation from the measured film thickness to fluid film pressure is not possible due to the severe noises of interferometric image over the contact area. Measuring technology of the EHL film thickness with nano-scale is also explained with regards to nano scale resolution.