How to use this calculator
- Enter actual pipe geometry. Use outside diameter and wall thickness from a schedule, SDR table, tube drawing or manufacturer data.
- Set allowable stress. Enter the project, material, code or manufacturer allowable hoop stress for the service condition.
- Apply factors. Set joint efficiency, temperature or service derating, and design factor if they are not already included.
- Check design pressure. Compare the calculated rating, required wall and utilization against the pressure you need to carry.
How it works
This page uses a Barlow thin-wall hoop-stress screen. First, the entered
allowable stress is adjusted for joint efficiency, temperature/service
derating and design factor:
S_adj = S x E x F / N
where S is allowable hoop stress, E is joint
efficiency, F is derating and N is the design
or safety factor.
Pressure rating is then:
P_rating = 2 x S_adj x t / OD
and the required wall thickness for the entered design pressure is:
t_req = P_design x OD / (2 x S_adj)
The calculator also reports hoop stress at design pressure, wall margin,
pressure utilization, inside diameter and OD/t ratio.
Pair this with the steel pipe schedule chart for actual OD and wall data, the pipe pressure drop calculator for steady head loss, water hammer calculator for surge pressure and pipe support span calculator for filled-pipe support spacing.
Worked example
Verified against the live calculator
A pipe with 2.375 in OD, 0.154 in wall,
20 ksi allowable hoop stress, E = 1.0,
F = 1.0 and N = 1.5 screens at about
1,730 psi. At 150 psi design pressure, the
required wall is about 0.013 in, so the entered wall has
large margin before any code, corrosion, tolerance or fitting limits.
Frequently asked questions
How do I calculate pipe pressure rating from wall thickness?
For a thin-wall screen, use Barlow pressure: P = 2 x S_adj x t / OD, where S_adj is allowable hoop stress after joint efficiency, derating and design factor, t is wall thickness and OD is outside diameter.
How do I calculate required pipe wall thickness?
Rearrange the same relation: t_req = P_design x OD / (2 x S_adj). The calculator compares that required wall with the wall thickness you entered.
Is Barlow formula valid for all pipes?
No. It is a thin-wall hoop-stress screen. Low OD/t ratios, thick-wall cylinders, pressure vessels, fatigue, external pressure, corrosion allowance and code-stamped piping need the applicable code or manufacturer rating.
Does this include corrosion allowance or mill tolerance?
No. Enter an effective wall thickness after any corrosion allowance, erosion allowance, thread/groove allowance, mill tolerance or project-specific deductions if those apply.
Can I use this for PVC, CPVC or HDPE pipe?
Only as a transparent stress screen with manufacturer-approved allowable stress and derating. Plastic pipe usually relies on long-term hydrostatic strength, SDR tables, temperature derating and listed pressure classes.
Method & assumptions
- Uses Barlow thin-wall hoop stress with actual outside diameter and effective wall thickness.
- Allowable stress is assumed to already reflect material, grade and service basis unless you add derating and design factor here.
- Wall margin is entered wall thickness minus required wall for the entered design pressure.
- OD/t is shown as a thin-wall warning screen; low ratios need thick-wall theory or the applicable code formula.
- Does not rate fittings, flanges, valves, joints, weld details, branch connections, external pressure, buckling, fatigue, corrosion allowance, mill tolerance, thread/groove deductions, plastic-pipe long-term hydrostatic strength, pressure cycles, temperature-specific manufacturer limits or code compliance.