With this online calculator you can calculate paint consumption for painting pipes.
Formula of surface area of pipe:
S = π * d * l
S - surface area of pipe
d - diameter of pipe
l - pipe length
Formula of volume of paint:
V = S * t * n
V - volume of paint
S - surface area of pipe
t - paint layer thickness
n - number of layers
Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film.