How to calculate the weight of seamless steel pipe

We know that the delivery weight of seamless steel pipe is generally calculated rather than weighed. Do you know how to calculate the weight of seamless steel pipe?

Formula for calculating the weight of seamless steel pipe:
(1) : if the density of steel (unit: g / cm3 or kg / m3) is 7.85, and the calculation formula of the seamless steel pipe weight per meter is:
W (kg / m) = 0.02466 * wall thickness *(outer diameter- wall thickness)

(2) : calculation formula for weight per meter of stainless steel (stainless acid resistant steel) pipe:
W (kg / m) = 0.02491 * wall thickness * (outer diameter- wall thickness)

(3) : calculation formula of cold drawn seamless rectangular steel pipe:
W (kg / m) = side length * 4 * thickness * 0.00785