By Zencalcy Editorial TeamLast reviewed About us
Engineers use this simplified formula to estimate the minimum wall thickness for a pipe carrying internal pressure. The full ASME B31.3 code includes additional allowances for corrosion, joint efficiency and temperature derating.
ASME B31.3 approximate wall thickness from pressure and allowable stress.
t = P D / (2 S + 2 Y P)
t is the wall thickness, P the internal pressure, D the outside diameter, S the allowable stress and Y the joint efficiency factor (typically 0.85 for threaded, 1.0 for welded). The formula assumes the outside diameter is known; if only the inside diameter is known, add twice the nominal thickness to approximate D.
| Symbol | Meaning |
|---|---|
| t | Wall thickness. |
| P | Internal pressure. |
| D | Outside diameter. |
| S | Allowable stress. |
| Y | Joint efficiency factor. |
t = 2×10⁶ × 0.5 / (2 × 150×10⁶ + 2 × 0.85 × 2×10⁶) ≈ 0.0048 m = 4.8 mm.
Continue with the Stress Calculator, Strain Calculator, or the Young's Modulus Calculator — or browse more materials and elasticity tools and all physics calculators.
Welded joints are usually stronger than the base metal, while threaded or flanged joints have reduced effective area. Y accounts for this.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026