Post / Column
Concentrated Load (lbs)
Calculate the total load on any concrete footing using tributary area, live load & dead load — then instantly find the required footing size, concrete volume, and bag count. IBC 2021 & ASCE 7-22 compliant.
Enter your structure type, tributary area & soil conditions to calculate footing load, required size & concrete needed.
Posts 8'×8' apart: 64 sq ft interior, 32 sq ft edge, 16 sq ft corner.
IBC Table 1607.1 — Residential Deck. Edit if your project differs.
Dead load = weight of structure itself (framing, decking, roofing, etc.)
A concrete footing load is the total vertical force (in pounds or kips) that a single footing must safely transfer from the structure above it into the supporting soil below. Every footing in a building — whether under a deck post, a house wall, or a garage column — collects load from a defined area of the structure called the tributary area. The footing must be wide enough so the resulting soil pressure (load ÷ footing area) does not exceed the soil's allowable bearing capacity. Underestimating footing loads is one of the leading causes of differential settlement, cracked foundations, and structural distress in residential construction across the USA.
Live Load (LL): Variable loads from occupants, furniture, snow, and equipment. For a residential deck, IBC Table 1607.1 requires 40 PSF live load. Dead Load (DL): The permanent weight of the structure itself — framing, sheathing, roofing, finishes, and the footing's own weight. A typical wood-framed floor has a dead load of 10–20 PSF. The total design load = Live Load + Dead Load, then multiplied by the tributary area to get pounds per footing. Visit asce.org for ASCE 7-22 load tables.
The tributary area is the floor or roof area that "feeds" its load to one specific footing. For an interior deck post in an 8'×8' grid, the tributary area is 64 sq ft. Edge posts share 32 sq ft; corner posts carry 16 sq ft. Multiply this area by the total load in PSF to get the load per footing in pounds.
If the footing load exceeds the soil bearing capacity, the footing punches into the ground — a failure mode called bearing failure or settlement. In clay-heavy soils (common in the Southeast, Oklahoma, and Texas), this can happen slowly over years. The fix is either a larger footing, deeper footing to reach better soil, or a helical pier system designed by an engineer.
Soil bearing capacities from IBC Table 1806.2 are presumptive values — meaning they are conservative estimates without a soil test. A 1.5× safety factor provides a reasonable buffer for variability in soil conditions, construction tolerances, and future load increases such as a roof addition, hot tub, or extra stories. For foundations, a 2.0× factor is more common.
The concrete footing load calculator uses the tributary area method — the standard approach for residential footing design in the USA under IBC 2021 and IRC 2021. The process has three steps: calculate the total load in pounds, size the footing to keep soil pressure below the allowable bearing capacity, and then calculate the concrete volume needed.
The load values in this calculator (40 PSF deck live load, 20 PSF dead load, etc.) are based on IBC 2021 Table 1607.1 and IRC R301.5 minimum values. Your local jurisdiction may require higher loads — particularly for snow loads in northern states, where ground snow loads can range from 20 PSF in Washington State to 100+ PSF in parts of New Hampshire, Vermont, and Alaska per ASCE 7-22 Figure 7.2-1. Always check with your local building department and use a city-specific concrete calculator for local conditions.
The table below shows typical live load and dead load values by structure type based on IBC 2021 Table 1607.1, IRC 2021 R301.5, and ASCE 7-22. These are the values pre-loaded in the calculator above. Use these as your starting point and adjust for your specific materials and local code requirements.
| Structure Type | Live Load (PSF) | Dead Load (PSF) | Total Design Load | Code Reference | Notes |
|---|---|---|---|---|---|
| Residential Deck | 40 PSF | 15 PSF | 55 PSF | IBC Table 1607.1 | Most common residential footing load |
| House Floor (Residential) | 40 PSF | 20 PSF | 60 PSF | IRC R301.5 | Includes framing, subfloor & finishes |
| Garage / Carport | 50 PSF | 20 PSF | 70 PSF | IBC 1607.1 | Vehicle load governs; 50 PSF minimum |
| Shed / Light Storage | 20 PSF | 10 PSF | 30 PSF | IRC R301.5 | Light storage use only |
| Flat Roof | 20 PSF | 15 PSF | 35 PSF | IBC 1607.11 | Add ponding allowance in flat climates |
| Roof — Moderate Snow Zone | 30 PSF | 15 PSF | 45 PSF | ASCE 7-22 | Pg 20–35 PSF ground snow (PA, OH, WA) |
| Roof — Heavy Snow Zone | 55 PSF | 15 PSF | 70 PSF | ASCE 7-22 | New England, N. Midwest — up to 100+ PSF |
| Pergola / Gazebo | 20 PSF | 10 PSF | 30 PSF | IRC R301.5 | Open structure; wind uplift may govern |
| Commercial / Assembly | 100 PSF | 25 PSF | 125 PSF | IBC 1607.1 | Requires licensed engineer — use as reference only |
The tributary area is the most misunderstood input in footing load calculations. It is simply the portion of the floor or roof area whose load is "collected" and delivered to one specific post or footing. The easiest way to find tributary area is to draw lines halfway between adjacent posts — the enclosed rectangle is the tributary area for the center post.
An interior post in an 8'×8' grid carries load from all four surrounding bays. Tributary area = 8 ft × 8 ft = 64 sq ft. This is the highest-loaded footing position and governs footing sizing for most decks and post-frame buildings.
A post at the edge (perimeter) of a structure shares load from only two bays — one on each side. For an 8'×8' grid: 8 ft × 4 ft = 32 sq ft. Edge posts carry roughly half the load of interior posts, so they can use a smaller footing.
A corner post sits at the intersection of only one bay from each direction. For an 8'×8' grid: 4 ft × 4 ft = 16 sq ft. Corner posts carry the lightest loads. However, in many structures, corner posts also resist lateral (wind/seismic) forces — which may require larger footings regardless of gravity load.
For two- and three-story structures, each story's floor load adds to the footing. A two-story house with 60 PSF per floor and 100 sq ft tributary area generates 12,000 lbs per footing. Always multiply by the number of floors above — footings at the base carry the cumulative weight of everything above.
Snow loads per ASCE 7-22 Figure 7.2-1 range from 0 PSF in Florida to 100+ PSF in parts of New Hampshire and Vermont. For roof-bearing footings in heavy snow zones (MN, WI, ME, NH, VT, AK), snow load is often the dominant design load — exceeding the live and dead loads combined.
A footing under a post receives a point load (concentrated at one location). A footing under a continuous wall receives a line load (pounds per linear foot). This calculator handles post/column point loads. For continuous wall footings, use the load per linear foot divided by the tributary length to get pounds per footing.
The table below shows the minimum round and square footing sizes required for common residential loads at various soil bearing capacities — based on IBC 2021 Table 1806.2 and a 1.5× safety factor. Use this as a quick sanity-check against your calculator results.
| Design Load (lbs) | Soil 750 PSF (Fill) | Soil 1,500 PSF (Clay) | Soil 2,000 PSF (Sand) | Soil 3,000 PSF (Common) | Soil 5,000 PSF (Gravel) |
|---|---|---|---|---|---|
| 1,000 lbs | 16" round / 14"×14" | 12" round / 10"×10" | 10" round / 10"×10" | 8" round / 8"×8" | 8" round / 8"×8" |
| 2,000 lbs | 24" round / 22"×22" | 16" round / 14"×14" | 14" round / 12"×12" | 10" round / 10"×10" | 8" round / 8"×8" |
| 3,000 lbs | 30" round / 28"×28" | 20" round / 18"×18" | 18" round / 16"×16" | 12" round / 12"×12" | 10" round / 10"×10" |
| 5,000 lbs | 38" round / 36"×36" | 26" round / 24"×24" | 22" round / 20"×20" | 16" round / 14"×14" | 12" round / 12"×12" |
| 8,000 lbs | 48" round / 44"×44" | 32" round / 30"×30" | 28" round / 26"×26" | 20" round / 18"×18" | 16" round / 14"×14" |
| 12,000 lbs | Engineer Required | 40" round / 38"×38" | 34" round / 32"×32" | 24" round / 22"×22" | 18" round / 16"×16" |
| 20,000 lbs | Engineer Required | Engineer Required | Engineer Required | 32" round / 30"×30" | 24" round / 22"×22" |
This calculator is designed for standard residential projects — decks, sheds, garages, and single-family homes up to 3 stories. You should always engage a licensed structural engineer if: (1) total load per footing exceeds 15,000 lbs; (2) your soil is fill, expansive clay, or has been disturbed; (3) the structure is in a high seismic zone (California, Pacific NW, parts of the Mountain West); (4) the building is commercial, multi-family, or over 3 stories; or (5) your local building department requires engineered drawings. No online calculator — including this one — replaces a licensed engineer for complex projects.
Project: 16'×20' deck in Columbus, OH. Posts at 8'×8' grid. Four interior posts, four edge posts, four corner posts. Soil: gravel/sand mix (3,000 PSF). Interior post: 64 sq ft × 55 PSF × 1.5 safety factor = 5,280 lbs design load → Required area: 5,280 ÷ 3,000 = 1.76 sq ft → 18" round Sonotube. Edge post: 32 sq ft × 55 PSF × 1.5 = 2,640 lbs → 12" round Sonotube. Corner post: 16 sq ft × 55 PSF × 1.5 = 1,320 lbs → 10" round Sonotube. See our patio concrete calculator for slab projects.
Trusted codes, standards, and tools for footing load calculations in the USA.
ASCE 7-22 (Minimum Design Loads for Buildings and Other Structures) is the definitive source for live loads, dead loads, snow loads, wind loads, and seismic loads used in US building design. All IBC 2021 load requirements reference ASCE 7-22.
Visit asce.orgThe International Building Code 2021 Table 1607.1 provides minimum live load values for all occupancy types, and Table 1806.2 gives presumptive soil bearing capacities used for footing sizing without a geotechnical report.
View IBC 2021 CodeThe American Wood Council's DCA6 Prescriptive Residential Wood Deck Construction Guide includes pre-engineered footing size tables for all 50 states — accounting for deck area, post spacing, and local snow loads. Free download available.
Visit awc.org