The Weight of Seawater in a Pipe calculator computes the weight (mass) of seawater in a pipe based on the density of the seawater (saltwater), the diameter and length of the pipe.
INSTRUCTIONS: Choose units and enter the following:
Weight of Seawater in a Pipe (M): The calculator returns the mass in kilograms. However, this can be automatically converted to compatible units via the pulldown menu.
The Weight of Sea Water in a pipe is calculated using the dimensions of the pipe (length and diameter) and the of the density of sea water. The formula for the weight of seawater in a pipe is:
M = μD • π • (D/2)² • L
where:
IMPORTANT NOTE: The above formula assumes that the pipe is full of seawater. A partially full pipe will have less water and weigh less. This calculation should be considered the maximum weight and does not include the weight of the pipe.
Common Mean Densities 
Natural
Food
Industrial
Fuels

Mean density is the average amount of mass within a volume for a substance. Note, volume of a material is often highly subject to the temperatures, since materials expand as they warm. For that reason, mean densities of substances are often cited with a set of nominal conditions such as temperature and barometric pressure.
The formula for mean density is:
μD = V / m
where:
Mean density is also often indicated as the Greek symbol rho (ρ).
The mean density of fluids can be useful since fluids (liquids and gases) conform to the shape of their containers. This is why it is possible to use the mean density of a substance and the dimensions of its container to estimate the weight/mass of the substance in the container.
And the mean density of sea water is a vCalc constant equal to 1,025 kilograms per cubic meter.