Barlow's Formula Calculator

Q: What is the Hoop Stress Formula for Pipe?

The standard equation for hoop stress is: H = PDm /2t. In this equation, H is allowable or hoop stress, the P is the pressure, t is the thickness of the pipe, and D is the diameter of the pipe.

Barlow’s Formula is a calculation used to show the relationship between internal pressure, allowable stress (also known as hoop stress), nominal thickness, and diameter. It is helpful in determining the maximum pressure capacity a pipe can safely withstand.

The formula is expressed as P=2St/D, where:

P: pressure, psig
t: nominal wall thickness, in inches(i.e. .375)
D: outside Diameter in inches
S: allowable stress in psi, which depends on the pressure being determined utilizing Yield or Tensile depending on what is trying to be determined

Specifically, Barlow’s Formula can be used to determine:

Internal Pressure at Minimum Yield:
S = SMYS - minimum yield for grade of pipe
Ultimate Bursting Pressure:
S = SMTS - minimum tensile strength for grade of pipe
Maximum Allowable Operating Pressure:
S = SMYS - reduced by a design factor
Mill Hydrostatic Test Pressure:
S = SMYS - reduced by a design factor depending on OD and grade

While this calculator is useful when planning your piping project, we recommend you contact us if you need additional information or have unusual or special applications.

Enter only 3 numeric values.

ATTRIBUTES	VALUE
P = Pressure	psig
t = Nominal Wall Thickness	inches
D = Outside Diameter	inches
S = Allowable Stress	psi.
Reset Calculate

Internal Burst Pressure Chart

	SCHEDULE 5S		SCHEDULE 10S		SCHEDULE 40S		SCHEDULE 80S
Nominal I.P.S. (in.)	Nominal O.D. (in.)	Wall (in.)	Pressure (p.s.i.)	Wall (in.)	Pressure (p.s.i.)	Wall (in.)	Pressure (p.s.i.)	Wall (in.)	Pressure (p.s.i.)
1/8	0.405			0.049	18150	0.068	25175	0.095	35175
1/4	0.54			0.065	18050	0.088	24450	0.119	33050
3/8	0.675			0.065	14450	0.091	20225	0.126	28000
1/2	0.84	0.065	11600	0.083	14825	0.109	19475	0.147	26250
3/4	1.05	0.065	9275	0.083	11850	0.113	16150	154	2200
1	1.315	0.065	7425	0.109	12450	0.133	15175	0.179	20425
1 1/4	1.66	0.065	5875	0.109	9850	0.14	12650	0.191	17250
1 1/2	1.9	0.065	5125	0.109	8600	0.145	11450	0.2	15800
2	2.375	0.065	4100	0.109	6875	0.154	9750	0.218	13775
2 1/2	2.875	0.083	4325	0.12	6250	0.203	10600	0.276	14400
3	3.5	0.083	3550	0.12	5150	0.216	9250
3 1/2	4	0.083	3100	0.12	4500	0.226	8475
4	4.5	0.083	2750	0.12	4000	0.237	7900
5	5.563	0.109	2950	0.134	3625	0.258	6950
6	6.625	0.109	2475	0.134	3050	0.28	6350
8	8.625	0.109	1900	0.148	2575	322	5600
10	1.75	0.134	1875	0.165	2300	0.365	5100
12	12.75	0.156	1825	0.18	2125	0.375	4400
14	14	0.156	1675	0.188	2025
16	16	0.165	1550	0.188	1775
18	18	0.165	1375	0.188	1575
20	20	0.188	1400	0.218	1625
24	24	0.218	1375	0.25	1550
30	30	0.25	1250	0.312	1550

*Bursting pressure calculated using Barlow's formula: P = 2ST/D

S=75,000 psi fiber stress

T=nominal wall

D=nominal O.D.=outside diameter

I.P.S.=inside pipe size

Download Printable Version of the Chart

Frequently Asked Questions About Barlow's Formula

What Does Barlow's Formula Determine?

Barlow's Formula is an equation that determines the relationship of internal pressure, allowable stress, nominal thickness, and diameter for pipe products.

What Type of Product is the Barlow's Formula Calculator Used For?

Barlow's Formula Calculator can be used to determine the maximum pressure capacity of line pipe. Worldwide pipe offers line pipe to a wide range of industries.

What is Hoop Stress?

Hoop Stress, also known as allowable stress, is the stress in a pipe wall. It is the circumferential force per unit areas (Psi) in the pipe wall caused by internal pressure.

What is the Hoop Stress Formula for Pipe?

The standard equation for hoop stress is H = PD_m /2t. In this equation, H is allowable or hoop stress, the P is the pressure, t is the thickness of the pipe, and D is the diameter of the pipe.