orders is magnitude & surface area: volume ratio

Each division or multiplication by 10 is termed one order of magnitude

E.g there is 1 order of magnitude between 2m and 20m

To change a measurement of nano metres into metres simply times by 10^{-9}

Surface area : volume

To find the surface area to volume ratio of something find the volume by multiplying height x width x depth. Then, for surface area calculate the area of each side and add up. Then put them in the ratio and get one of then simplify (get to 1 being 1 if possible). As the size of a cube decreases by a factor of ten (order of magnitude) the SA:V ratio will increase by a factor of ten.