Soil Bearing Capacity Calculator

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Soil Bearing Capacity Calculator

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Estimate soil bearing capacity for different soil types and moisture levels. Includes safety factor and maximum safe load calculation. Free geotechnical calculator.

Unit System:

Soil Type

Moisture Level

Safety Factor *

Range: 1.5-5.0 (typical 2.0-3.0)

Footing Width (m) - Optional

Enter to calculate maximum safe load

Footing Length (m) - Optional

Enter to calculate maximum safe load

Results

Bearing Capacity

OK

Base Capacity

150.00 kN/m²

Sand (moist)

Allowable Capacity

60.00 kN/m²

Safety factor: 2.5

Warnings

This is a BASIC ESTIMATOR only. Actual bearing capacity MUST be determined through professional soil testing and geotechnical analysis.
Always consult a qualified geotechnical engineer before construction.

Capacity Breakdown

Soil Type

Sand

Moisture Level

Moist

Base Capacity

150.00 kN/m²

Safety Factor

2.5

Soil Type Comparison

Base capacity (moist)

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Soil Bearing Capacity Calculator — Complete Geotechnical Guide

Estimate ultimate and allowable bearing capacity for isolated, strip, and raft foundations using Terzaghi, Meyerhof, and IS 6403 methods. Includes settlement checks for safe geotechnical design.

FOS = 3

Typical safety factor for footings

≤ 25 mm

Max settlement for isolated footings (IS 1904)

150–300 kPa

Allowable SBC of medium-dense sand

1943

Year Terzaghi published his bearing capacity theory

How Soil Bearing Capacity is Determined

Ultimate bearing capacity (q_ult) is the maximum pressure per unit area at which the soil beneath a footing will shear and fail — the classic Terzaghi failure mechanism where a punching or general shear wedge forms under the footing and the surrounding soil heaves. The allowable bearing capacity (q_a) divides this by a factor of safety (typically 2.5–3.0) to account for uncertainties in soil data, load estimation, and construction variability.

However, ultimate capacity is only half the story. In many soils — particularly soft clays, loose sands, and fills — the foundation will reach intolerable settlement long before shear failure. IS 1904 limits isolated footing settlement to 25 mm and differential settlement to 20 mm for buildings on sand; for raft foundations, 65 mm total and 25 mm differential. Serviceability often governs in soft soils even when the bearing capacity safety factor is comfortable.

Field investigation informs the design: the Standard Penetration Test (SPT) N-value correlates empirically to bearing capacity and relative density of sand; the Cone Penetration Test (CPT) gives continuous stratigraphy; laboratory triaxial and direct shear tests measure the cohesion c and friction angle φ needed for Terzaghi / Meyerhof equations. Never rely on table values alone for structural foundations — always verify with site-specific borings or trial pits.

Design Checklist

✔Confirm soil classification (IS 1498 / USCS / AASHTO)

✔Obtain SPT N-values or CPT qc at footing level

✔Determine water table depth (reduces effective stress)

✔Select footing type: isolated / strip / raft / pile

✔Calculate q_ult using Terzaghi or Meyerhof method

✔Apply FOS 2.5–3.0 → allowable SBC

✔Check settlement: total ≤ 25 mm, differential ≤ 20 mm

✔Review net vs gross bearing capacity distinction

Bearing Capacity Formulas

Terzaghi's general shear (strip footing)

q_ult = c·Nc + q·Nq + 0.5·γ·B·Nγ
where q = γ·Df (overburden pressure)

Nc, Nq, Nγ are Terzaghi bearing capacity factors (functions of φ). For square footings: 1.3cNc + qNq + 0.4γBNγ. For circular: 1.3cNc + qNq + 0.3γBNγ. Valid for general shear only (dense sand / stiff clay).

Meyerhof general formula (IS 6403)

q_ult = c·Nc·Fcs·Fcd·Fci
       + q·Nq·Fqs·Fqd·Fqi
       + 0.5·γ·B·Nγ·Fγs·Fγd·Fγi

F_s = shape, F_d = depth, F_i = inclination correction factors. IS 6403 recommends Meyerhof factors with Indian practice modifications. More versatile than Terzaghi — handles inclined loads, sloped ground, and eccentric loads.

Allowable bearing capacity & safe load

q_a = q_ult / FOS   (typically FOS = 3.0)
P_safe = q_a × A_footing
A_footing = column load / q_a

Net bearing capacity: q_net = q_ult − γDf. For existing footings already embedded, use net values. For new footings, use gross q_ult / FOS. Always check both gross and net to be conservative.

Settlement (elastic — Bowles)

S_i = q·B·(1−μ²)/E_s · I_w
S_i ≤ 25 mm (isolated), ≤ 65 mm (raft)

μ = Poisson ratio (0.3 sand, 0.45 clay), E_s = soil modulus (MPa), I_w = influence factor (shape/rigidity). Consolidation settlement in clay: S_c = Cc·H/(1+e₀) × log[(σ₀+Δσ)/σ₀]. Consolidation often governs over shear in soft clays.

Soil Types — Typical Bearing Capacities

Soil Type	Allowable SBC (kPa)	SPT N-value	φ (degrees)	Behaviour
Hard / dense rock (basalt, granite)	3000–10000	N/A (rock)	—	Elastic — no shear failure; settlement negligible
Soft rock (sandstone, limestone)	600–3000	N/A	—	Elastic; check for jointing and dissolution features
Dense sand / gravel (well graded)	300–600	> 50	38–45°	General shear; settlement in mm range; water table critical
Medium-dense sand	150–300	10–50	30–38°	Moderate bearing; settlement in 25–50 mm range
Loose sand / fill	50–150	< 10	< 30°	Local/punching shear; settlement often governs; liquefaction risk
Stiff clay (cu > 100 kPa)	150–300	15–30	φ = 0 for undrained	Undrained bearing controls short-term; consolidation long-term
Medium clay (cu 50–100 kPa)	75–150	5–15	φ = 0 undrained	Significant consolidation settlement; needs surcharge timing
Soft clay (cu < 50 kPa)	< 75	< 5	φ = 0 undrained	Settlement governs; piled or raft foundation usually required

Source: IS 1904:1986, BS EN 1997-1:2004, NAVFAC DM-7. Tabulated values are for preliminary design only; site-specific investigation is mandatory for all structural foundations.

History of Geotechnical Engineering

1773

Charles-Augustin de Coulomb publishes his earth pressure theory, including the wedge failure mechanism and the equation τ = c + σ tan φ (cohesion + friction), which remains fundamental to soil mechanics two and a half centuries later. Coulomb was designing retaining walls for French military fortifications.

1856

Henry Darcy publishes his law of flow through porous media (Q = kAi), establishing the mathematical framework for groundwater flow and consolidation. Darcy's Law underpins all seepage, drainage, and pore-pressure analysis in geotechnical engineering.

1909

Probable year of the first systematic use of the Standard Penetration Test (SPT) in the United States, developed by engineers at the Raymond Concrete Pile Company. The SPT N-value remains the most widely used in-situ soil test globally, correlating to bearing capacity, relative density, and liquefaction susceptibility.

1925

Karl von Terzaghi publishes Erdbaumechanik (Soil Mechanics), founding soil mechanics as a scientific discipline. He introduces effective stress (σ' = σ − u), consolidation theory, and the first rigorous bearing capacity analysis. Terzaghi is universally regarded as the "father of soil mechanics."

1943

Terzaghi publishes Theoretical Soil Mechanics, including his landmark bearing capacity equations (q_ult = cNc + qNq + 0.5γBNγ) for strip footings with general shear failure. George Meyerhof later extends these (1951, 1963) to include shape, depth, and inclination factors, creating the IS 6403 framework used today.

1994–2004

Eurocode 7 (EN 1997) is developed and published, harmonising geotechnical design across Europe with a limit-state design approach (ULS + SLS) replacing allowable stress design. Partial factors replace global FOS = 3; Design Approach 1/2/3 offers alternative load-resistance factoring. Most European countries now use EC7 as the primary geotechnical design code.

Codes & Standards

IS Code India

IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations (India)

The primary Indian standard for bearing capacity calculations. Adopts Meyerhof's general formula with shape, depth, and inclination correction factors. Covers strip, isolated, and raft foundations; includes SPT-based correlations for sand and SPT-to-cu correlations for clay. Mandatory for Indian construction.

Eurocode Europe

EN 1997-1:2004 — Eurocode 7: Geotechnical Design (Europe)

The European limit-state geotechnical design standard. Replaces global FOS with partial factors on soil strength and structural loads. Design Approaches 1, 2, and 3 give alternative partial factor sets. Annex D provides analytical bearing resistance formulae equivalent to Meyerhof. Used across 30+ European countries.

ASCE / NAVFAC USA

ASCE 7-22 & NAVFAC DM-7 (USA)

ASCE 7-22 provides load combinations for geotechnical design; NAVFAC DM-7 (Design Manual 7, Naval Facilities Engineering Command) is the US reference manual for soil mechanics and foundation engineering, with comprehensive bearing capacity tables, SPT correlations, and settlement charts widely cited in US practice.

Soil Bearing Capacity Myths vs Facts

Myth

If the soil doesn't sink when you walk on it, it can take any building load

Fact

Soil failure is not visible underfoot — a person exerts about 30 kPa (standing) to 150 kPa (stiletto heel), while a 10-storey building exerts 150–300 kPa over its full raft area. Soil that feels solid underfoot may be soft clay capable of only 50–75 kPa allowable pressure. Always investigate with borings — visual inspection cannot determine bearing capacity.

Myth

A higher FOS (factor of safety) is always safer

Fact

Increasing FOS beyond 3.0 increases foundation size and cost but does not improve safety if settlement governs. In soft clays, serviceability (settlement ≤ 25 mm) often controls long before shear failure. An oversized shallow footing on soft clay will still settle excessively. The correct response to poor soil is to change the foundation type (piles, raft), not simply raise FOS.

Myth

The water table depth has no effect once foundations are above it

Fact

The water table reduces effective stress in the soil below it, potentially halving the bearing capacity contribution of the depth term (qNq) and the width term (0.5γBNγ) if the water table is at or above footing level. IS 6403 requires correction factors for water table position. Even seasonal water table fluctuation must be considered — design for the worst-case water level.

Myth

SPT N-values directly give allowable bearing capacity

Fact

SPT N-values are correlated empirically to bearing capacity (e.g., Terzaghi & Peck chart, IS 6403 Table 1), but these correlations have wide scatter bands (±50%). The same N=20 value in a fine-grained or gravelly sand will give very different actual bearing capacity. SPT N-values are a screening tool; detailed laboratory tests (triaxial, consolidation) are needed for final design of important structures.

Frequently Asked Questions

What is the typical allowable bearing capacity of ordinary residential soil in India?▾

IS 1904:1986 and empirical data suggest: hard murum / laterite — 200–350 kPa; medium dense sand — 150–250 kPa; firm clay — 100–150 kPa; soft clay or black cotton soil — 50–75 kPa. For a typical 2-storey house, contact pressure is about 50–100 kPa — most soils can handle this, but differential settlement in expansive (black cotton) soil is the real risk, not bearing failure.

What is the difference between gross and net bearing capacity?▾

Gross bearing capacity is the total pressure at the base of the footing (including the weight of soil above footing level before excavation). Net bearing capacity subtracts the overburden pressure that existed before construction (net q_ult = gross q_ult − γDf). For new footings, use net values to avoid crediting soil weight that was always there. The distinction matters most for deep footings.

Why is a factor of safety of 3 commonly used for foundations?▾

FOS = 3 on ultimate bearing capacity is a long-established empirical value that implicitly covers: uncertainty in soil shear strength parameters (c and φ), spatial variability of soil, quality of site investigation, errors in load estimation, and construction tolerance. IS 6403 allows FOS = 2.5 when settlement analysis is done separately, as some safety reserve is already embedded in the settlement limit check.

What is punching shear failure vs general shear failure?▾

General shear failure (Terzaghi's classic mechanism): the footing pushes a wedge of soil downward; log-spiral failure surfaces develop; and the surrounding soil heaves upward. Occurs in dense sand and stiff clay. Punching shear failure: the footing sinks without a clear failure wedge; surrounding soil compresses vertically without heaving. Occurs in loose sand, soft clay, and deep footings. Local shear failure is an intermediate case. Terzaghi's original equations apply to general shear; use 2/3c and tan(2/3φ) for local/punching shear.

How does the water table depth affect the bearing capacity calculation?▾

IS 6403 requires reducing the unit weight of soil (to submerged weight γ' = γ_sat − 9.81 kN/m³) when: (a) the water table is at the foundation base — the Nγ term (width term) uses γ'; (b) the water table is within a depth B below the footing — a linear interpolation between full γ and γ' applies to the Nγ term; (c) the water table is above the footing — both Nq and Nγ terms use γ'. Water table at footing level can reduce bearing capacity by 35–50% in dense sand.

What is the minimum depth of a foundation as per IS 1080?▾

IS 1080:1985 specifies minimum foundation depth = 500 mm below natural ground level for residential buildings on ordinary soils. IS 1904 recommends: below frost depth (not applicable in most of India); below the zone of seasonal moisture change (typically 0.6–1.5 m in expansive soils); and below any loose fill or vegetable matter. Black cotton soil requires a minimum depth of 1.2–1.5 m to get below the shrink-swell active zone.

When is a raft (mat) foundation required instead of isolated footings?▾

IS 2950 recommends raft foundations when: (1) individual footing areas would cover more than 50% of the plan area; (2) differential settlement is expected to be large (soft clay, filled ground); (3) the structure is sensitive to differential settlement (storage tanks, turbine foundations); (4) soil bearing capacity is very low (< 50 kPa) and piles are not feasible; (5) adjacent structures constrain the excavation footprint. Raft distributes the total building load over the entire plan area, reducing contact pressure.

What is the safe bearing capacity of black cotton soil?▾

Black cotton soil (expansive Vertisol) has allowable SBC of 50–100 kPa in the dry state, but swells dramatically when wetted (up to 50% volume change) and shrinks on drying — creating large differential movements. IS 1904 recommends: found below the active zone (1.2–1.5 m minimum); use isolated footings connected by grade beams; treat sub-grade with lime or fly ash stabilisation; or use bored cast-in-situ piles extending to stable strata at 3–5 m depth.

How do I choose between Terzaghi and Meyerhof bearing capacity methods?▾

Terzaghi's equations are simpler and conservative — suitable for preliminary sizing and for footings under concentric vertical loads. Meyerhof's method (adopted in IS 6403) is more versatile: it handles eccentric loads (from moments), inclined loads (from wind, seismic), sloped ground, and better accounts for shape and depth. For final structural design, IS 6403 (Meyerhof-based) is the required Indian standard; Eurocode 7 Annex D uses a similar approach.

What is the relationship between SPT N-value and bearing capacity per IS 6403?▾

IS 6403 Table 1 gives safe bearing capacity for sand (for footings of width B = 0.3–3 m at depth Df = 0.5–2 m): N = 10 → q_s ≈ 100–150 kPa; N = 20 → 200–250 kPa; N = 30 → 300–350 kPa; N > 50 → 500+ kPa. These are conservative lower-bound estimates. Note that IS 6403 values include settlement check to 25 mm; you do not need to add a separate settlement factor for these table values. Apply water table correction if applicable.

What causes differential settlement and how can it be prevented?▾

Differential settlement occurs when different parts of the foundation settle by different amounts — caused by: (1) variable soil stiffness or layer thickness beneath the footprint; (2) adjacent footings with very different loads; (3) eccentric loading; (4) nearby excavation removing lateral support; (5) soil shrinkage/swelling (expansive clays). Prevention: uniform site investigation to characterise variability; equalize contact pressure across all footings; use raft or deep piles in variable soils; provide continuous reinforced grade beams linking isolated footings; avoid founding at different levels on sloping soil.

How do I account for seismic effects on soil bearing capacity?▾

IS 1893:2016 Clause 6.3.5 requires checking for liquefaction of saturated sandy soils (SPT N < 15) in seismic zones III–V. Liquefaction causes complete loss of bearing capacity during strong shaking. For non-liquefiable soils, IS 1893 allows increasing allowable SBC by 25% for short-duration seismic loads (since sustained overload is not the mechanism). Deep sandy fills below the water table in seismic zones may require ground improvement (dynamic compaction, stone columns) regardless of static bearing capacity.

References

IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations, BIS
IS 1904:1986 — Code of Practice for Design and Construction of Foundations in Soils: General Requirements, BIS
Terzaghi, K. (1943) — Theoretical Soil Mechanics, John Wiley & Sons
Meyerhof, G.G. (1963) — "Some Recent Research on the Bearing Capacity of Foundations," Canadian Geotechnical Journal 1(1):16–26
EN 1997-1:2004 — Eurocode 7: Geotechnical Design — Part 1: General Rules, CEN
Das, B.M. (2021) — Principles of Foundation Engineering, 9th Ed., Cengage Learning

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Soil Bearing Capacity Calculator

Calculate soil bearing capacity using Terzaghi & Meyerhof methods. Get allowable pressure, safety factors & foundation recommendations. Free geotechnical tool.

Methodology, sources & limitations

This calculator uses a published formula and the values entered in the calculator to generate the result.

Formula: q_u = c'Nc + γDfNq + 0.5γBNγ (Terzaghi's equation)
Jurisdiction & units: Intended for US, IN, EU, GB, AU. Supports both units where applicable.
Assumptions & limitations: Results are preliminary estimates based on the inputs you provide. Confirm material properties, loads, local codes, and final designs with a qualified professional.
Review status: Formula and automated QA completed June 21, 2026; independent professional review is pending. Next scheduled review: September 21, 2026.

Validation sources

IS 6403
Terzaghi (1943)

Soil Bearing Capacity Calculator — Answer & Method

Calculate safe bearing capacity of soil for foundation design.

Formula: Soil Bearing Capacity

q_u = c'Nc + γDfNq + 0.5γBNγ (Terzaghi's equation)

- = See calculator (various)

Example Calculation

Use the Soil Bearing Capacity Calculator for accurate calculations.

Important limitation

Use this as a preliminary estimate and verify project-specific inputs, codes, and designs with a qualified professional.

Key Facts

Terzaghi's bearing capacity equation is the foundation of modern geotechnical design.

Sources & Validation

IS 6403Terzaghi (1943)

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Soil Bearing Capacity Calculator

Results

Soil Bearing Capacity Calculator — Complete Geotechnical Guide

How Soil Bearing Capacity is Determined

Design Checklist

Bearing Capacity Formulas

Soil Types — Typical Bearing Capacities

History of Geotechnical Engineering

Codes & Standards

IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations (India)

EN 1997-1:2004 — Eurocode 7: Geotechnical Design (Europe)

ASCE 7-22 & NAVFAC DM-7 (USA)

Soil Bearing Capacity Myths vs Facts

Frequently Asked Questions

References

Related Calculators

Design Safe Foundations with Confidence

Soil Bearing Capacity Calculator

Methodology, sources & limitations

Validation sources

Soil Bearing Capacity Calculator — Answer & Method

Formula: Soil Bearing Capacity

Example Calculation

Important limitation

Key Facts

Sources & Validation

Related Calculators

See Also

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Retaining Wall Calculator

Soil Bearing Capacity Calculator

Results

Soil Bearing Capacity Calculator — Complete Geotechnical Guide

How Soil Bearing Capacity is Determined

Design Checklist

Bearing Capacity Formulas

Soil Types — Typical Bearing Capacities

History of Geotechnical Engineering

Codes & Standards

IS 6403:1981 — Code of Practice for Determination of Bearing Capacity of Shallow Foundations (India)

EN 1997-1:2004 — Eurocode 7: Geotechnical Design (Europe)

ASCE 7-22 & NAVFAC DM-7 (USA)

Soil Bearing Capacity Myths vs Facts

Frequently Asked Questions

References

Related Calculators

Design Safe Foundations with Confidence