How do I calculate footing size?

Divide the total column load (plus a small self-weight allowance) by the soil's safe bearing capacity to get the required area, then take the square root for a square footing. For 500 kN on 150 kN/m² soil, that is about 3.67 m², or a 1.95 x 1.95 m footing.

What is safe bearing capacity?

It is the maximum pressure the soil can carry safely. It ranges from about 75 kN/m² for soft clay to 900+ for rock. The real value for your site must come from a soil test, not a textbook table.

Does this design the footing reinforcement?

No. This tool only estimates the footing footprint (plan size). Depth, reinforcement, shear checks and settlement must be designed by a structural engineer per IS 456. Footings are safety-critical.

What size footing for a 2-storey house?

It depends entirely on the column loads and soil, which vary by design and site, so there is no single answer. Estimate the load per column, enter it with your soil's bearing capacity, and always confirm with an engineer.

Footing Size Calculator — Isolated Column Footing (India)

How footing size is estimated

An isolated (pad) footing spreads a column's load over enough soil that the pressure stays within what the ground can safely carry. The required plan area is simply the total load divided by the safe bearing capacity (SBC) of the soil. This tool adds a ~10% allowance for the footing's own weight and backfill, then converts the area into a length and breadth (square by default), rounded up to a buildable size, and checks that the resulting soil pressure stays within the SBC.

This is a sizing estimate, not a design. A real footing design also fixes the depth, the reinforcement (both ways), and checks one-way and two-way (punching) shear, bending, and settlement — all using factored loads per IS 456 and an actual geotechnical report for the SBC. Never build a footing from this number alone; use it to sanity-check sizes and discuss with your engineer.

Safe bearing capacity by soil

SBC is the safe pressure a soil can carry, and it varies enormously: soft clay may be only 75 kN/m², medium sand around 200, dense gravel 450, and rock 900 or more. These textbook values are indicative starting points only — the real SBC for your site comes from a soil test, and using a wrong (especially too-high) value is dangerous because the footing would be undersized.

Worked example

For a column carrying 500 kN on medium clay (SBC 150 kN/m²): with a 10% self-weight allowance the load is 550 kN, so the required area is 550 ÷ 150 = 3.67 m², giving a square footing of about 1.95 × 1.95 m. The actual pressure under that footing is about 145 kN/m², just within the 150 limit. For the concrete and steel in that footing once sized, use the column & footing material calculator.

Footing Size Calculator

Footing inputs

Estimated footing size

How footing size is estimated

Safe bearing capacity by soil

Worked example

Footing size — common questions