SCH 20 Steel Pipe Dimensions and Thickness Chart

SCH 20 steel pipe is one of the lighter wall thickness schedules used in low-pressure piping systems. Although it is not as commonly referenced as Schedule 40 or Schedule 80, it still plays an important role in applications where flow capacity matters more than pressure resistance.

This guide breaks down SCH 20 steel pipe dimensions, wall thickness, and practical usage in a clear, engineering-based way—without unnecessary complexity.
 

What is SCH 20 Steel Pipe?

Schedule 20 (SCH 20) refers to the wall thickness classification of a steel pipe under ASME B36.10 and B36.19 standards.
In simple terms:
The higher the schedule number ， the thicker the wall
SCH 20 ：relatively thin wall pipe
Designed for low-pressure and non-critical systems
 

SCH 20 Steel Pipe Dimensions Overview

Unlike pressure rating, SCH 20 dimensions depend mainly on outside diameter (OD) and wall thickness.Below is a standard reference chart used in industry practice.

Pipe size	Outside Diameter (OD) in Inch	Outside Diameter (OD) in mm	SCH 20 Wall thickness in Inch	SCH 20 Wall thickness in mm	SCH 20 Weight in lb/ft	SCH 20 Weight in kg/m
8″ NPS200	8.625	219.1	0.25	6.35	22.36	33.31
10″ NPS250	10.75	273	0.25	6.35	28.04	41.77
12″ NPS300	12.75	323.8	0.25	6.35	33.38	49.73
14″ NPS350	14	355.6	0.312	7.92	45.61	67.9
16″ NPS400	16	406.4	0.312	7.92	52.27	77.83
18″ NPS450	18	457	0.312	7.92	58.94	87.71
20″ NPS500	20	508	0.375	9.53	78.6	117.15
22″ NPS550	22	559	0.375	9.53	86.61	129.13
24″ NPS600	24	610	0.375	9.53	94.62	141.12
26″ NPS650	26	660	0.5	12.7	136.17	202.72
28″ NPS700	28	711	0.5	12.7	146.85	218.69
30″ NPS750	30	762	0.5	12.7	157.53	234.67
32″ NPS800	32	813	0.5	12.7	168.21	250.64
34″ NPS850	34	864	0.5	12.7	178.89	266.61
36″ NPS900	36	914	0.5	12.7	189.57	282.27

otes:
The inner diameter (ID) is approximate and can vary slightly based on manufacturing tolerances.
Larger pipe sizes for SCH 20 are available upon request.
Dimensions are based on ANSI/ASME standards for steel pipes.

NPS (Nominal Diameter) ≠ Actual Inner Diameter
This is a common misconception. For example, a pipe with NPS 12" has an actual outer diameter of 323.8 mm (approximately 12.75 inches), not 12 inches.
The golden rule: When NPS ≤ 12 inches, NPS corresponds neither to the outer nor the inner diameter; it's merely a designation. Only when NPS ≥ 14 inches does the NPS value essentially equal the actual outer diameter (in inches) of the pipe.

 

Schedule 20 Pipes Wall Thickness

Nominal Pipe Size (NPS)	Outer Diameter (OD) (inches)	Wall Thickness (inches)	Wall Thickness (mm)
1/2″	0.84	0.065	1.65
3/4″	1.05	0.065	1.65
1″	1.315	0.065	1.65
1-1/4″	1.66	0.065	1.65
1-1/2″	1.9	0.065	1.65
2″	2.375	0.065	1.65
2-1/2″	2.875	0.065	1.65
3″	3.5	0.065	1.65
4″	4.5	0.083	2.11
6″	6.625	0.083	2.11
8″	8.625	0.083	2.11

Notes:
Wall thickness values are based on ASME B36.10M standards.
For larger sizes or additional wall thickness options, custom solutions may be available.
The above data applies to steel pipes commonly used in low-pressure applications.
Common Applications of SCH 20 Steel Pipe

SCH 20 pipes are widely used in

HVAC chilled water systems
Fire sprinkler auxiliary lines (low-pressure sections)
Agricultural irrigation
Light industrial fluid transfer
Structural tubing in non-load critical areas
 

Conclusion

SCH 20 steel pipe is a lightweight, cost-efficient piping option designed for low-pressure systems where flow efficiency matters more than strength. While not suitable for heavy-duty industrial pressure applications, it remains a practical choice in HVAC, drainage, and light fluid transport systems.

Understanding SCH 20 dimensions and wall thickness helps engineers avoid over-design or under-specification—both of which can affect system performance and cost.