Estimate allowable and ultimate pile capacity by soil type. Calculates skin friction and end bearing components using simplified formulas. For preliminary assessment only — a licensed geotechnical engineer must perform site-specific design.
Pile installation accuracy starts with proper layout. A Spectra SP60 or Trimble SPS986 rover keeps pile positions within tolerance.
Shop Express Tools →This calculator uses a simplified static pile capacity model. Total ultimate capacity is the sum of skin friction resistance along the pile shaft and end bearing at the pile tip.
Unit skin friction (fs) and unit end bearing (qp) values are representative estimates for each soil type. Actual values depend on soil density, water content, pile material, and installation method. A geotechnical report with site-specific boring data and in-situ testing is required for final design.
| Soil Type | Unit Skin Friction (ksf) | Unit End Bearing (ksf) | Typical Use |
|---|---|---|---|
| Loose Sand | 0.05–0.15 | 5–15 | Low capacity; avoid if possible |
| Dense Sand | 0.20–0.40 | 40–80 | Good for driven piles |
| Soft Clay | 0.05–0.20 | 3–8 | Friction pile; watch settlement |
| Stiff Clay | 0.20–0.40 | 10–20 | Adequate skin friction |
| Gravel | 0.25–0.45 | 60–100 | Excellent end bearing |
Values are representative ranges. Actual values must be determined by a licensed geotechnical engineer from site borings and testing.
Pile capacity estimates are used during early project planning and bid preparation to determine whether the specified pile size and length are consistent with the soil conditions. Estimators use preliminary calculations to anticipate pile quantities and lengths before geotechnical reports are finalized. Field superintendents use capacity references when reviewing pile installation records to flag anomalies in driving resistance (blow count) relative to expected capacity.
During construction, capacity is typically verified through dynamic pile testing (PDA — Pile Driving Analyzer) or static load tests per ASTM D1143. Wave equation analysis (WEAP) is also commonly used to correlate blow count to capacity during production driving. This calculator does not replace those methods.
Ultimate pile capacity is the theoretical maximum load the pile can carry before failure — the sum of skin friction resistance along the pile shaft and end bearing resistance at the pile tip. Allowable capacity is the ultimate capacity divided by a safety factor, typically 2.0 to 3.0. Allowable capacity is what engineers specify in pile schedules and what contractors use for load limits in the field.
Skin friction (also called shaft resistance) is the resistance developed along the surface of the pile shaft as it interacts with surrounding soil. In cohesive soils (clay), this is related to undrained shear strength. In granular soils (sand, gravel), it depends on the lateral earth pressure and interface friction angle. Skin friction typically contributes the majority of pile resistance in long friction piles embedded in uniform soil.
End bearing capacity is the resistance developed at the pile tip as it bears against the soil or rock below. It depends on the tip area and the bearing capacity of the soil at depth — dense sands, gravels, and rock produce high end bearing; soft clays produce low end bearing. Short piles bearing on competent material are often designed as end bearing piles. Long piles in soft soils are typically friction piles.
Safety factor selection depends on the quality of subsurface information, pile testing program, and engineer judgment. SF = 2.0 is appropriate when static load tests confirm capacity. SF = 2.5 is standard for most driven pile designs without load testing. SF = 3.0 is conservative and used when soil data is limited or conditions are uncertain. The geotechnical engineer of record specifies the design safety factor — do not apply this calculator for structural design without engineering review.
This calculator provides preliminary estimates using simplified unit skin friction and end bearing values for common soil types. It does not account for pile installation method, soil stratification, pore water pressure, group effects, negative skin friction, pile material (concrete vs. steel vs. timber), or depth-dependent lateral pressure. A licensed geotechnical engineer performing a site-specific analysis with actual boring data and CPT results will produce substantially more accurate results. Use this tool for quick order-of-magnitude estimates only.
The formulas used approximate behavior of driven or bored friction and end bearing piles in typical soil conditions. The calculator does not distinguish between pile material types (concrete, steel H-pile, pipe pile, timber, micro-pile) or installation method (driven vs. drilled). Different pile types develop resistance differently — steel H-piles have lower perimeter area than concrete round piles of similar size. For specific pile types, apply the appropriate unit resistance values from your geotechnical report.