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Pile Capacity Calculator

N value for sand, cu for clay: shaft and base worked separately, then divided by a factor of safety.

Also known as pile load capacity · pile bearing capacity · driven pile capacity

Quick answer

With the default inputs: Pile diameter 0.6 m · Pile length 20 m · Soil type Sand etc.Allowable capacity 1508 kN

Use your own dimensions ↓

Inputs

blows/300mm
kPa

Result

Allowable capacity
1508kN
Perimeter1.885m
Base area0.2827m²
Unit shaft friction40.0kPa
Shaft capacity1508kN
Unit end bearing8000kPa
Base capacity2262kN
Ultimate capacity3770kN
Base share of total60%
MethodSPT (Meyerhof)
How this is worked out

Shaft and base resistance are computed separately because they mobilise at very different settlements: shaft friction peaks at roughly 0.5% of the diameter, end bearing needs 5-10% of the diameter to fully develop. Adding ultimate values and dividing once is therefore optimistic — practice applies a larger factor to the base or caps the unit end bearing. The SPT route uses fs = 2N kPa and qb = 400N kPa (Meyerhof); the clay route uses the alpha method with fs = alpha x cu (alpha typically 0.5) and qb = 9cu. These are preliminary correlations that scatter by about 30%, so a real design needs a static load test or dynamic testing. Correct N to N60 and to an effective overburden of 100 kPa before using it — uncorrected blow counts in loose saturated sand under-read and under-predict capacity. For pile groups, apply a group efficiency reduction below 3D spacing.

Next up: Bearing Capacity Calculator · Retaining Wall Stability Calculator

Formula

Perimeteru = π·D
Base areaAb = π·D²/4
Shaft, sandfs = 2N (kPa, cap 100)
Base, sandqb = 400N (kPa, cap 15000)
Shaft, clayfs = 0.5·cu
Base, clayqb = 9·cu
UltimateQu = fs·u·L + qb·Ab
AllowableQa = Qu / FS
600 mm diameter, 20 m long, sand with N = 20, factor of safety 2.5: perimeter 1.885 m, base area 0.2827 m², fs = 40 kPa giving 1508 kN shaft, qb = 8000 kPa giving 2262 kN base, 3770 kN ultimate and 1508 kN allowable, with the base carrying 60%.

Basis

FAQ

How do I calculate the capacity of a single pile?
Two parts. Shaft capacity is unit shaft friction times perimeter times length; base capacity is unit end bearing times base area. Add them for ultimate capacity and divide by the factor of safety, normally 2.5, for the allowable value. Unit values come from soil type: for sand use SPT and take fs = 2N kPa with qb = 400N kPa; for clay use fs = 0.5cu and qb = 9cu. Always benchmark the result against a load test before it goes into a construction drawing.
Is a 60% base share realistic?
For a short pile founded on a stiff layer, yes. For a long pile with a slenderness ratio above 25 it is a warning sign, usually meaning the N value is too high or the base sits on a sand layer with soft clay beneath. Check two things: at least 3D of competent soil below the base, otherwise the end bearing is lost to the soft layer beneath; and for high slenderness, reduce the base term for settlement rather than taking the full 400N.

What to calculate next

These jobs are done back to back on site — follow the steps to work through the whole sequence.

Foundations: when bearing capacity is not enoughStep 2 of 4

  1. 1Bearing Capacity Calculator
  2. 2Pile Capacity Calculator
  3. 3Pile Cap Calculator
  4. 4Bored Pile Concrete and Rebar Calculator

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Pile Capacity Calculator. 2026-10-25. https://jianzhujisuan.com/en/pile-capacity

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.