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Pile Load Capacity Calculator

Enter the pile dimensions and soil resistances to estimate its load capacity.

How it is calculated

The tool models a round pile with a flat base and the same soil resistance along the whole shaft. Base area is Ab = π d² / 4 and shaft area is As = π d L, with diameter d and embedded length L in metres. End bearing is Qp = qb × Ab, skin friction is Qs = fs × As, where qb and fs are soil pressures in kPa (kN/m²), so the results are in kN. Ultimate capacity is Qu = Qp + Qs and allowable capacity is Qall = Qu / FS. All five inputs are needed, and diameter, length and FS must be above zero. The tool does not check that FS is at least 1, and it ignores pile weight, layered soils, group effects and settlement.

Worked example

A 0.6 m diameter, 15 m long pile with end bearing of 3,000 kPa, skin friction of 40 kPa and a factor of safety of 2.5. Base area: π × 0.6² ÷ 4 = 0.2827 m², so Qp = 3,000 × 0.2827 = 848.23 kN. Shaft area: π × 0.6 × 15 = 28.27 m², so Qs = 40 × 28.27 = 1,130.97 kN. Ultimate capacity: 848.23 + 1,130.97 = 1,979.20 kN. Allowable capacity: 1,979.20 ÷ 2.5 = 791.68 kN. Here friction supplies more than half of the capacity because the pile is long.

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Common mistakes

  • Entering the diameter in millimetres or centimetres. The field is in metres, so 600 instead of 0.6 inflates the result by a factor of about a million.
  • Entering end bearing or skin friction in kN, MPa or tonnes per square metre. Both fields expect kPa.
  • Applying one skin friction value to every soil layer. Real piles pass through layers with different resistances, and a single average can mislead.
  • Reading the ultimate capacity as the design load. Design uses the allowable value after the factor of safety.
  • Treating a single-pile result as the capacity of a pile group. Neighbouring piles interact, so a group is not simply the sum of its piles.

About this calculator

A deep foundation pile carries load through two mechanisms working together: end bearing, where the pile tip transfers force directly into a strong soil or rock layer, and skin friction, where the shaft's outer surface resists movement through the soil it passes through. The ultimate bearing capacity is the sum of these two contributions; dividing it by a factor of safety (typically 2 to 3, depending on soil investigation quality and local code) gives the allowable capacity that a structural engineer actually designs against.

This calculator takes a pile's dimensions along with end-bearing and skin-friction soil resistance values and returns both the ultimate and allowable load capacity. Geotechnical and structural engineers sizing deep foundations, foundation contractors reviewing a pile design before installation, and civil engineering students working through bearing-capacity problems use it to check that a proposed pile diameter and length can safely carry the structural loads above it before drilling or driving equipment ever gets mobilized.

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