Foundation Load Calculator

Total your building loads and size the footing for your soil, plus wind uplift and anchoring for sheds.

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Roof dead load, 15 psf x 17.0 ft255 plf
Roof snow, 30 psf x 17.0 ft510 plf
Floor dead load, 1 floor at 10 psf x 8.0 ft80 plf
Floor live load, 1 floor at 40 psf x 8.0 ft320 plf
Wall, 10 psf x 9 ft90 plf
Footing self-weight, 12 x 8 in100 plf
Total line load1,355 lb per ft
Footing width12 in (IRC minimum 12 in)
Footing thickness8 in (IRC minimum 6 in)
Bearing pressure1,355 of 1,500 psf allowable
Concrete0.25 cu yd per 10 ft of footing

Turn these numbers into a build plan.

  • 1,355 plf line load
  • 12 x 8 in footing
  • 2.5 cu yd concrete
Soil bearing90% of allowable
Show the formulas

Strip footing: line load w = sum of (load psf x tributary width) + wall weight, then width B = w / (allowable bearing - footing weight). Pier: area A = P / (allowable bearing - footing weight), side = square root of A.

Next: the concrete and forms in the concrete footing calculator, bars and laps in the footing rebar calculator, and deck piers in the deck footing size calculator.

Next you will need

Concrete Footing CalculatorFooting Rebar Calculator

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Project plan · built from your numbers

12 in wall footing for a 1-story house

A load of 1,355 lb per foot on clay, silt, sandy clay (1,500 psf) needs a footing 12 in wide and 8 in thick, 2.5 cu yd for 100 ft.

Materials
$687
Time
1 to 2 weeks with inspection
Level
Advanced
5 steps 4 tools 3 materials
  1. 1

    Confirm soil and frost depth

    Ask the building department for the frost depth and presumptive soil bearing, or get a soil test.

  2. 2

    Lay out and dig

    Set batter boards and strings, then dig to undisturbed soil below frost.

  3. 3

    Form and reinforce

    Set forms 12 in apart and place rebar on chairs with 3 in cover.

01 · Your numbers
Line load
1,355 plf
Footing
12 x 8 in
Concrete
2.5 cu yd
Est. cost
$687
02 · The plan

5 steps · 4 tools · 3 materials

2 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

Your plan is 60% built. Save it.

3/5

12 in wall footing for a 1-story house

Finished in 1 to 2 weeks with inspection · $687 DIY

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Worked examples

  1. One-story frame house on clay. 32 ft deep, 30 psf snow, crawlspace: 1,355 lb per ft, so a 12 x 8 in footing at 1,355 psf on 1,500 psf soil.
  2. Two-story brick veneer on sand. 2,565 lb per ft on 3,000 psf soil: 12 x 8 in.
  3. 10 x 12 shed, 115 mph. Velocity pressure 24.5 psf, uplift 2,702 lb, lateral 2,987 lb: 4 helical anchors.

Soil bearing capacity

Presumptive allowable bearing, IRC Table R401.4.1
SoilAllowable bearing
Clay, silt, sandy clay1,500 psf
Sandy or silty gravel2,000 psf
Sand, gravel3,000 psf
Sedimentary rock4,000 psf
Crystalline bedrock12,000 psf

Footing width by house and soil

This calculator, 32 ft deep house, 30 psf snow, framed floors, 8 in footing. IRC R403.1: never under 12 in wide or 6 in thick.
HouseClay 1,500Silty gravel 2,000Sand 3,000
1 story, light frame12 in12 in12 in
1 story, brick veneer14 in12 in12 in
2 story, light frame16 in12 in12 in
2 story, brick veneer22 in16 in12 in
3 story, light frame20 in16 in12 in
3 story, brick veneer30 in22 in14 in

Footings go below the frost line, which runs from a few inches in the South to 4 ft or more up north; ask the building department. Then size the pour with the concrete footing calculator and the steel with the footing rebar calculator. Decks and porches: deck footing size and deck beam span. Columns: concrete column calculator.

When you need an engineer

More than two stories, expansive clay, fill or a slope, a point load over about 10,000 lb, a retaining wall, or a building department that asks for stamped drawings. Background on how bearing capacity is worked out is on Wikipedia.

Foundation load calculator FAQ

How do I calculate the load on a foundation?

Add the loads that reach each foot of wall: roof dead and snow load times half the roof span, each floor's dead and live load times its tributary width, and the wall's own weight. Add the footing's weight and divide by the soil's allowable bearing to get the width.

How wide should a footing be for a 2-story house?

For a 32 ft deep house with 30 psf snow, our math gives 16 in on clay for light frame and 22 in with brick veneer; on sand and gravel it drops to 12 in. IRC Table R403.1 sets the prescriptive minimums, and local code governs.

What is soil bearing capacity and how do I find mine?

The pressure the soil can carry without settling too much. Without a soil test, codes allow presumptive values: 1,500 psf for clay, 2,000 for silty gravel, 3,000 for sand and gravel. Your building department may set the local value.

Do I include snow load?

Yes, the roof snow load from your local code (often 20 to 70 psf, much more in the mountains). The calculator adds it to the roof's dead load.

Strip footing or piers?

Strip footings carry walls continuously and suit houses with basements or crawlspaces. Piers carry posts at points and suit decks, porches, sheds and pier-and-beam houses.

How thick should a footing be?

At least 6 in under the IRC, and at least as thick as it projects past the wall for unreinforced concrete. 8 to 12 in is common.

How much wind uplift does a shed see?

A 12 x 10 ft shed in open terrain at 115 mph sees about 2,702 lb of net roof uplift after counting 60% of its weight, which is why sheds need 4 or more anchors.

When do I need an engineer?

Over two stories, on expansive clay or fill, on slopes, for point loads over about 10,000 lb, retaining walls, or whenever the building department asks. This calculator is for planning.

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