Deck Footing Size Calculator

Inputs

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Gravity load carried by one footing or post location before the entered load factor.
lbf
Multiplier applied to the entered service load before comparing soil bearing.
Entered allowable bearing pressure for the supporting soil. The calculator does not choose this value.
psf
Used for selected-area utilization and concrete quantity.
Trial round footing or tube diameter to check.
in
Concrete thickness or depth for quantity only. Structural thickness/punching checks are outside this screen.
in
Number of similar footings for total concrete quantity.
footings
Normal-weight concrete is often around 2300-2400 kg/m^3.
lb/ft³

Results

Default result
Edit inputs
Required bearing area(A_req)
2.667ft²
Pass

Design load divided by entered allowable soil bearing.

Also computed

Required round diameter(D_req)22.11in

Diameter of a round footing with the required bearing area.

Required square width(B_req)19.6in

Side length of a square footing with the required bearing area.

Selected bearing area(A_sel)3.142ft²

Actual soil pressure(q_actual)Pass1,273psf

Below the entered allowable soil bearing.

Bearing utilization(U)Pass0.849

Actual soil pressure divided by entered allowable soil bearing.

Bearing load margin(P_margin)712.4lbf

712.4 lbf

Positive load margin against entered soil bearing.

Deck footing bearing preview: utilization 0.85, within entered soil bearingDeck footing bearing previewRequired area from load divided by entered allowable soil bearing.selected footing bearing areabearing utilization0.85soil pressure61.0 kPamargin3.2 kN
Method notes 4 notes
  • Required bearing area A_req = P*F/q_allow, with q_allow supplied by the user/project.
  • Round diameter D_req = sqrt(4*A_req/pi); square width B_req = sqrt(A_req).
  • Selected thickness/depth is used for concrete quantity only; this does not check frost depth, punching shear, uplift, lateral loads, post bases, reinforcement, settlement or permit requirements.
  • Pair this with the concrete-bag takeoff page if you need bag yield rounding for a purchased premix product.

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