How this calculator works
A full straight pipe is a cylinder of liquid. Its actual internal diameter determines capacity, which is often different from the nominal pipe size. Multiply capacity by liquid density for contained mass. Reverse length and diameter accept either known volume or known mass with density. Fittings, valves, air pockets and partially filled sections are excluded from the cylindrical estimate.
Formula
V = pi x internal diameter^2 x length / 4; liquid mass = density x V; length = 4V / (pi D^2); diameter = sqrt(4V / (pi length)); density = mass / V.
Worked example
A 1 m internal-diameter pipe 2 m long holds pi/2 = 1.570796 m3. At 1000 kg/m3 the liquid mass is 1570.796 kg. Using that capacity and diameter recovers the 2 m length.
Advertisement
Frequently asked questions
Should I use outside diameter?
No. Capacity uses the inside diameter after subtracting wall thickness. Pipe material mass uses the annulus instead.
Does water always have density 1000 kg/m3?
That is a useful approximate input. Temperature and dissolved substances change density; use measured values when precision matters.
Can a bent pipe be estimated?
Use its internal centreline path length if the section stays circular and constant. Add fittings or reservoirs with different capacities separately.