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    Mechanical / Tanks

    Storage Tank Shell

    Shell plate thickness for an above-ground storage tank to API 650, by the one-foot method. The thickness changes with each course because the pressure depends on the height of product above the point.

    Bottom course10.4 mmCalculated t8.4 mmTop course2.6 mm
    Bottom course
    10.4 mm
    Including allowance
    Calculated t
    8.4 mm
    One-foot method
    Top course
    2.6 mm
    Near the top
    Product head
    118 kPa
    At the base
    Course thickness
    API 650 one-foot method: t = 4.9·D·(H − 0.3)·G / (S·E) + CA.
    Course thickness
    Course height (m)Thickness (mm)
    12.5
    33.9
    66.1
    98.3
    1210.4
    Inspect the model
    Choose a quick result view, a scaled comparison, or the complete diagnostic set.
    Thickness against liquid height
    Linear in height, which is why a tank is built from courses.
    Thickness against liquid height0.0002.825.648.4611.2814.103 m3 m6 m6 m9 m9 m12 m12 m15 m15 mStorage Tank Shell
    Canonical equations
    The exact relationships implemented by this engine.

    t = 4.9·D·(H − 0.3)·G/(S·E) + CA · API 650 one-foot method.

    p = ρ·g·H · Hydrostatic pressure at the base.

    engineering methodology

    A clear path from inputs to results.

    Shell plate thickness for an above-ground storage tank to API 650, by the one-foot method. The thickness changes with each course because the pressure depends on the height of product above the point.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Set tank diameter (m).
    2. Set design liquid height (m).
    3. Set product specific gravity.
    4. Set allowable stress (mpa).
    5. Read the headline metrics, then check the table for the detail.

    The formula

    t=4.9⋅D⋅(H−0.3)⋅G/(S⋅E)+CAt = 4.9·D·(H − 0.3)·G/(S·E) + CA

    Reference: API 650 §5.6 one-foot method for shell thickness.

    Worked example

    At the default inputs

    Inputs
    • Tank diameter (m): 20; Design liquid height (m): 12; Product specific gravity: 1; Allowable stress (MPa): 160; Joint efficiency: 0.85; Corrosion allowance (mm): 2
    Calculation path
    1. 1

      Bottom course: 10.4 mm · Calculated t: 8.4 mm · Top course: 2.6 mm · Product head: 118 kPa

    Result

    Bottom course: 10.4 mm · Calculated t: 8.4 mm · Top course: 2.6 mm

    Interpreting the result

    A 20 m tank 12.0 m tall needs 10.4 mm at the bottom course.

    Assumptions & limitations

    • Above-ground, atmospheric tank.
    • No seismic or wind overturning.

    Frequently asked questions

    Why does thickness change by course?

    The pressure depends on the height of product above the point.

    What is the one-foot method?

    It takes the design point one foot above the bottom of each course, which is accurate enough for most tanks.

    Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.