> ## Documentation Index
> Fetch the complete documentation index at: https://calcs.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Design a Spread Footing (IBC 2024)
> Design isolated spread footings to ACI 318-19 per IBC 2024 (ASCE 7-22): bearing, flexure, one-way and punching shear, and development length.
Column loads link directly from the calculations above, so changes propagate to the footing automatically. Design isolated spread footings to ACI 318-19 per IBC 2024. Results cover bearing capacity under service loads, flexural design, one-way shear, two-way (punching) shear, and development lengths.
Learn how to design a simple residential concrete spread footing in Calcs.com, including specifying soil properties, load, footing size, and reinforcement.
## Method & scope
| Property | Detail |
| ---------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | IBC 2024 (ACI 318-19 and ASCE 7-22) |
| Regions | United States |
| What it checks | Bearing pressure and stability, Uplift safety factor, Flexural capacity (ACI 318-19, Cl. 22.2), One-way (beam) shear (ACI 318-19, Cl. 22.5), Two-way (punching) shear (ACI 318-19, Cl. 22.6), Development of reinforcement (ACI 318-19, Cl. 25.4), Column-footing interface bearing (ACI 318-19, Cl. 22.8) |
#### See the exact clause
Every check in this calculator links back to its governing clause in ACI 318-14. Open the **Formula Reference** panel on any result and select the clause reference to read it. See [Viewing Clauses from Inside a Calculator](/docs/running-calculations/standards-and-codes/viewing-clauses-from-inside-calculator).
#### Calculation method
The Spread Footing (IBC 2024) calculator designs isolated rectangular spread footings to ACI 318-19 as referenced by IBC 2024, with ASD and LRFD load combinations from ASCE 7-22 (Ch. 2). Service loads govern soil bearing and stability; factored loads govern the reinforced-concrete strength design. It handles concentric and eccentric (moment) loading and checks the full set of geotechnical and concrete limit states.
##### Bearing pressure and stability
Service-level column loads are combined through the ASCE 7-22 ASD combinations and resolved into a soil bearing pressure profile under the footing. Under moment, an iterative procedure covers the partial-contact (Zone 2) eccentricity case where part of the footing lifts off the soil:
**utilization = q\_max / q\_allow ≤ 1.0**
where q\_allow is the allowable gross bearing capacity. Overturning and sliding are checked as factors of safety against user-set minimums:
**FS\_overturning = M\_resisting / M\_overturning ≥ FS\_min**
**FS\_sliding = (mu × N) / V ≥ FS\_min**
both evaluated on the X and Y axes.
##### Uplift safety factor
Net uplift from wind or seismic combinations is resisted by the footing and soil self-weight:
**FS\_uplift = W\_resisting / T\_net ≥ FS\_min**
The column self-weight is not counted in the uplift resistance.
##### Flexural capacity (ACI 318-19, Cl. 22.2)
Factored bending moments at the face of the column are computed on each axis and compared to the reduced flexural capacity of the reinforced section:
**utilization = M\_u / (phi × M\_n) ≤ 1.0**
checked for X-axis and Y-axis bottom reinforcement. Where the bottom bars cannot develop, the calculator also evaluates whether a plain-concrete section passes. Negative bending (top reinforcement) capacity is checked on both axes for uplift or eccentric cases.
##### One-way (beam) shear (ACI 318-19, Cl. 22.5)
One-way shear demand is taken at a distance d from the column face and compared to the concrete shear strength (no shear reinforcement is assumed):
**utilization = V\_u / (phi × V\_c) ≤ 1.0**
##### Two-way (punching) shear (ACI 318-19, Cl. 22.6)
Punching shear is checked on the critical perimeter located d/2 from the column face:
**utilization = v\_u / (phi × v\_c) ≤ 1.0**
with v\_c taken as the governing of the code expressions (aspect ratio, perimeter ratio, and the base term).
##### Development of reinforcement (ACI 318-19, Cl. 25.4)
The required development length of the flexural bars is checked against the length available from the critical section to the bar end, applying the standard modification factors. Excess reinforcement area is credited to reduce the required length, and top-bar development is checked separately.
##### Column-footing interface bearing (ACI 318-19, Cl. 22.8)
Bearing stress where the column lands on the footing is compared to the concrete bearing capacity, which is increased by the square root of the ratio of the supporting area to the loaded area (capped per code). Bearing dowels are sized where the interface bearing is exceeded.
##### Assumptions
The column is centered on the footing and designed separately. Compression reinforcement is not counted in bending strength, and no shear reinforcement is considered. For steel base plates, only concrete bearing under concentric load is checked; eccentric (moment) interface bearing is verified separately. The column self-weight is not counted in the uplift check.
## How to use it
The **Spread Footing calculator** (ACI 318-14, ACI 318-19, and IBC 2024 versions) computes sliding resistance using **base friction only**:
**Sliding resistance = μ × (P + W\_f)**
where **μ** is the lateral sliding coefficient between concrete and soil, **P** is the ASD axial load, and **W\_f** is the factored footing and soil self-weight. The sliding demand vs. resistance breakdown is shown when the results section is expanded.
**Passive earth pressure is not modeled** as a resistance term. There are no inputs for a passive pressure coefficient, embedment depth for passive resistance, or soil shear strength, and it is not listed in the assumptions.
If passive pressure is a significant contributor to sliding resistance for your design, you'll need to evaluate it separately outside the calculator and combine it manually with the calculator's friction resistance.
#### Design a Concrete Spread Footing to ACI 318-14
#### Uplift Safety Factor Check for Footings
## Common questions
The calculator designs the concrete section to ACI 318-19 as referenced by IBC 2024, with ASD and LRFD load combinations from ASCE 7-22 (Ch. 2). Service-level loads govern soil bearing and stability; factored loads govern the reinforced-concrete strength checks. This is the current edition for 2024 IBC projects.
Key inputs are footing width, length, and thickness, concrete strength and density, column width and length (or base plate dimensions) with any X and Y offset, allowable gross soil bearing capacity, depth and unit weight of soil over the footing, sliding friction coefficient, concrete cover, reinforcement yield strength and bar counts for each axis, and bearing dowels. Applied column loads (axial, moment, shear) can be entered manually or linked from a column calculation above.
It checks soil bearing pressure under service loads (including the partial-contact eccentric case), overturning and sliding factors of safety, an uplift safety factor, flexural capacity at the column face on both axes, one-way (beam) shear, two-way (punching) shear, development of the flexural reinforcement, and concrete bearing at the column-footing interface. Demand, capacity, and utilization are reported for each check.
Yes. Axial load plus biaxial moment is resolved into a bearing pressure profile, with an iterative procedure for the partial-contact (Zone 2) case where part of the footing lifts off the soil. Rectangular footings are supported, and reinforcement is checked independently on the X and Y axes.
Top reinforcement is checked for negative bending, which can arise under uplift or large eccentric moments that reverse the bending on part of the footing. Enter top bar counts and spacing, and the calculator evaluates negative-bending flexural capacity and top-bar development on both axes alongside the bottom-reinforcement checks.
Yes. If a column calculation sits above the footing in the same Calcs.com project, the axial force, moment, and shear at the column base link directly. When the column loading, section, or height changes, the footing automatically re-runs bearing, flexure, one-way shear, punching shear, and interface bearing with the updated reactions, no manual re-entry.
## Next steps
Design combined rectangular footings for two columns to ACI 318-19 per IBC 2024: bearing, overturning, sliding, flexure, shear and development length.
Design pier, pole and deck-post footings to ACI 318-19 per IBC 2024 (ASCE 7-22): embedment, bearing, bending, shear and uplift.
Design continuous wall footings to ACI 318-19 per IBC 2021 or IBC 2024. Results cover ultimate load, bearing capacity and serviceability.
How Calcs.com finds soil pressures on a spread footing under bending in both directions at once, and how to do the same by hand.
