Calculate maximum pipe pressure rating with Barlow’s formula from outside diameter, wall thickness and allowable stress in psi, bar or MPa.
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Pipe Pressure Rating Formula
The pipe pressure rating calculator uses Barlow’s formula to estimate the maximum internal pressure a pipe wall can withstand based on allowable stress, wall thickness, and outside diameter.
P = (2*S*t)/D
- P = maximum pressure rating
- S = allowable stress of the pipe material
- t = pipe wall thickness
- D = pipe outside diameter
In By Material mode, the calculator uses the selected material’s allowable stress value. It converts the outside diameter and wall thickness to inches, then calculates pressure in psi.
In Custom Stress mode, you enter the allowable stress directly. The calculator converts the stress to psi if needed, converts the dimensions to inches, and applies the same formula.
The result is shown in psi, with equivalent values in bar, kPa, and MPa.
Typical Allowable Stress Values Used
| Material | Allowable Stress | Common Use |
|---|---|---|
| A53 Carbon Steel | 16,000 psi | General steel piping |
| A106 Grade B Steel | 17,100 psi | High-temperature service |
| 304 / 316 Stainless Steel | 18,800 psi | Corrosion-resistant piping |
| Copper Type L | 6,000 psi | Plumbing and water lines |
| PVC Schedule 40 | 2,000 psi | Low-pressure plastic piping |
| HDPE PE4710 | 1,600 psi | Water and gas distribution |
Pressure Range Reference
| Calculated Pressure | General Interpretation |
|---|---|
| Less than 50 psi | Very low pressure service |
| 50 to 150 psi | Similar to many water supply systems |
| 150 to 500 psi | Low-pressure industrial service |
| 500 to 1,500 psi | Common industrial process range |
| Above 1,500 psi | High-pressure service requiring careful design review |
Example Problems
Example 1: Carbon steel pipe
You have A53 carbon steel pipe with an outside diameter of 2.375 in and a wall thickness of 0.154 in. The allowable stress is 16,000 psi.
P = (2*16000*0.154)/2.375
The pressure rating is about 2,075 psi.
Example 2: Custom allowable stress
You enter a custom allowable stress of 10,000 psi, an outside diameter of 4.5 in, and a wall thickness of 0.237 in.
P = (2*10000*0.237)/4.5
The pressure rating is about 1,053 psi.
FAQ
Does this calculator give the final safe working pressure?
Not by itself. Barlow’s formula gives a pressure estimate based on stress, wall thickness, and diameter. Actual allowable working pressure can also depend on temperature, corrosion allowance, weld efficiency, fittings, code requirements, safety factors, and pipe condition.
Should I use outside diameter or inside diameter?
This calculator uses outside diameter because the implemented Barlow formula is based on outside diameter. Entering inside diameter will change the result and can overstate or understate the pressure rating.
Why does wall thickness have such a large effect?
Pressure rating is directly proportional to wall thickness. If the wall thickness doubles and the material and diameter stay the same, the calculated pressure rating also doubles.
