Definition
Outside Diameter — Outside diameter (OD) is the external diameter of a tubular's body, a primary sizing dimension that, with nominal weight and grade, identifies drill pipe and determines annular clearance in the wellbore.
Also known as: outside diameter, outer diameter, OD
What outside diameter is
Outside diameter (OD) is the external diameter of a pipe’s tube body. It is the headline sizing number for tubulars — 3-1/2 in, 5 in, 5-1/2 in drill pipe, and so on — and, combined with nominal weight (wall) and grade, it fully specifies the pipe. Note that the tool joint OD on drill pipe is larger than the tube OD, and it is the tool joint that usually contacts the wellbore wall.
The OD sets the annular clearance between the string and the borehole or casing, which affects hole cleaning, circulating pressures and the risk of getting stuck.
Why it matters
- Annular clearance — larger OD reduces the annulus, raising annular velocity but also the risk of pack-off.
- Section modulus — a larger OD gives more tensile and torsional capacity for the same wall.
- Tool joint OD — governs wear against casing and the pass-through of the string in tight holes.
Renting by OD
Choosing OD balances strength and hydraulics against hole and casing clearance. We rent drill pipe and drill collars in the common ODs — contact us to match pipe and tool-joint OD to your hole size.