Measuring steel pipe size accurately is crucial for selection, installation, and system compatibility. Here’s a simple guide on how to measure steel pipe size step-by-step, whether for standard pipes (e.g. plumbing) or industrial use.
1. Identify the Pipe Type First
Steel pipes are usually classified into:
Nominal Pipe Size (NPS) — commonly used in North America (e.g. NPS 2, NPS 4)
Outside Diameter (OD) + Wall Thickness — used in many international and industrial standards (e.g. OD 60.3 mm, wall 3.91 mm)
DN (Diameter Nominal) — metric designation (e.g. DN50 ≈ 2” NPS)
2. Measure the Outside Diameter (OD)
Use a caliper (preferred) or measuring tape.
Wrap it around the pipe if using a tape, or measure straight across the outside of the pipe with calipers.
Example:
If OD = 60.3 mm (or 2.375 inches), it corresponds to NPS 2.
3. Measure the Wall Thickness
Use a caliper to measure from the outside to the inner wall (if cut pipe is available).
Or measure inside diameter (ID) and subtract from OD:
Wall Thickness=OD−ID2\text{Wall Thickness} = \frac{OD - ID}{2}Wall Thickness=2OD−ID
Example:
OD = 60.3 mm, ID = 52.5 mm → wall thickness = (60.3 - 52.5)/2 = 3.9 mm
4. Determine the Nominal Pipe Size (NPS) or DN
Use OD and wall thickness to reference pipe size charts (since NPS is not always equal to OD).
For example:
OD ≈ 60.3 mm → NPS 2 (DN50)
OD ≈ 114.3 mm → NPS 4 (DN100)
5. Measure the Pipe Length (if needed)
Use a tape measure to record total straight length.
Tip: Common Pipe Schedules
Pipe schedule (SCH) refers to wall thickness:
SCH 10, 20, 40, 80, 160, etc.
Higher number = thicker wall
For example, NPS 2:
SCH 40 wall = 3.91 mm
SCH 80 wall = 5.54 mm
