You will need
Determine the radius of the tube R. If you want to calculate internal volume of pipe, it is necessary to find the inner radius. If you want to calculate the volume occupied by the pipe, we should calculate the radius. By measurements it's easy to get the diameter (both internal and external) and the length of the circumferential section of the pipe. If you know the diameter of the pipe, divide it into two. So, R=D/2 where D is the diameter. If you know the circumference of the cross section of the pipe, divide it by 2*PI, where PI=3.14159265. So, R=L/6,28318530, where L is the circumference.
Find the area of the cross section of the pipe. Raise the value of the radius squared and multiply it by PI. Thus, S=PI*R*R, where R is the radius of the tube. The cross-sectional area will be found in the same system of units, which had taken the radius value. For example, if the radius value is represented in centimeters, the cross-sectional area is calculated in square centimeters.
Calculate the volume of the pipe. Multiply the sectional area of the pipe to the length. The volume of the pipe V=S*L, where S is the cross-sectional area and L is the length of the pipe.
Make sure to use the values of radius and length of the pipe expressed in the same units of measurement.
When the calculator, store in his memory the number of 2*PI. So you can easily calculate several values of the volume of tubes with different radii.