Outer Diameter (OD)

Definition - What does Outer Diameter (OD) mean?

The outer diameter (OD) of a hollow circular object, such as a pipe, is a measurement of the distance of a straight line from one point on the outer wall of the object, through its center, to an opposite point also on the outside. The outer diameter of a pipe, together with its wall thickness, are essential to inside diameter calculations.

Outer diameter is also known as outside diameter or external diameter.

Trenchlesspedia explains Outer Diameter (OD)

The outer diameter of a pipe should not be confused with the nominal diameter. The nominal diameter is essentially a number that defines the size of the pipe, while the corresponding outer diameter is usually a bit larger. For example, for a 4” schedule 80 pipe, 4” is the nominal size of the pipe, while the actual outer diameter is 4.5”. Unlike the inner diameter, the pipe’s outer diameter is not dependent on its thickness.

In trenchless construction, the outer diameter of a pipe is typically crucial for installation techniques requiring boring, such as horizontal directional drilling (HDD), pipe jacking and microtunneling.

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