Learn · guide

How to use the pad footing calculator

Column loads in, a base and a bar mat out: what each input means, how to read the bearing pressure and the governing check, and when to press Optimise size.

All guides Inputs Result Calc sheet Walk-through Mistakes

1. What the calculator does

The pad footing calculator sizes and reinforces an isolated pad under a column. It checks the soil bearing pressure for the column loads and moments, then designs the base as reinforced concrete: bending each way, one-way (beam) shear, punching shear at the column face and at the critical perimeter, minimum steel, cover and bar spacing. It can also find the smallest base that passes.

The code routes are SANS 10100, BS 8110, Eurocode 2 / EC7 (EN 1992-1-1) and SANS 51992-1-1 (SA Eurocode, 2023 draft annex) / EC7. The bearing check uses an allowable bearing pressure on the SANS and BS routes; on the EN route the soil check follows EC7.

Pad footing calculator header with the PASS badge — The header: PASS 90 %, governed by durability (nominal cover). The tabs open the checks, drawing and calc sheet.

2. The inputs, group by group

Input	What it means	Typical value
Footing	A mark (F1...) and the design code.	F1, SANS 10100
Column loads	Characteristic loads at the column top: N, M_x, M_y, H_x, H_y for dead, live and wind. Take them from the column or beam reactions.	Dead N 550, live N 250 kN
Base	Width B along x, length L along y and depth h.	2.5 × 2.5 × 0.6 m
Column	Column size c_x × c_y; it sets the punching perimeter.	400 × 400
Soil	Allowable bearing pressure q_all from the geotechnical report.	150 to 300 kPa
Materials	Concrete f_cu and rebar f_y.	30 MPa, 450 MPa
Durability	Cover and exposure. A footing cast against the soil needs more cover than one cast on blinding.	50 mm, in contact with soil
Bars	The engine picks a mat each way. “Bars and starters” lets you set them and the column starters.	Y12 @ 125 each way

Pad footing inputs: column loads table, base, column, soil, materials, durability and bars — The inputs. The column loads table is characteristic, at the column top: one row for dead, live and wind.

3. How to read the result

The plan shows the base, the column and the bars each way; section A–A shows the column, the loads with their arrows, the base depth and the stub. Under it the soil bearing pressure diagram gives q_max and q_min. With a moment or a horizontal load the pressure is not uniform: q_max must stay under the allowable pressure, and q_min should stay above zero (no uplift under the base).

Footing plan, section A-A and the soil bearing pressure diagram — Plan, section A–A and the soil pressure. Here q_max is 179.9 kPa against an allowable 200 kPa.

The badge names the governing check. In the default example it is durability (nominal cover) at 90 %, not bearing or punching: worth knowing before you make the base bigger. Any check the engine could not run shows as NOT CHECKED; it is not a pass.

“Optimise size” searches for the smallest base B × L × h that passes, on the STATIX server. Use it for a first size, then round to sizes you can set out.

Design checks summary, optimise size and bending schedule card — Right column: the design checks, “Optimise size (min cost)” and the bending schedule card with “+ Add to a project”.

4. Calc sheet, drawing and schedule

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The bending schedule card reads: “Sign in (free): 3 schedules a month. CSV with a paid plan.” The reinforcement detail drawing and the export to STATIX 2D are part of the paid plan.

Reinforcement detail panel marked paid plan — The full reinforcement detail drawing, sections and bar editing are part of the paid plan.

Lower down, the verification table runs published pad footing examples through the same engine and shows the published value, the calculator value and the difference.

Verification table comparing published examples with the calculator — Verification: each published case, its source, the published value, the calculator value and the difference.

5. A 2-minute walk-through

Open the calculator. It starts with a 400 × 400 column carrying dead 550 kN and live 250 kN with small moments and shears, on a 2.5 × 2.5 × 0.6 m base and 200 kPa soil.
Read the badge: PASS 90 %, governed by the nominal cover. q_max is 179.9 kPa.
Press “Optimise size” and see how small the base can go. Look at what governs now: often bearing or punching.
Add a wind moment in the wind row and watch q_max and q_min spread apart.
Sign in for the calc sheet and the schedule, or press “+ Add to a project”.

6. Common mistakes

Ultimate loads in the loads table. The table takes characteristic loads; the engine builds the combinations.
An ultimate bearing value as the allowable pressure. Use the allowable (working) value from the geotechnical report on the SANS and BS routes.
Ignoring q_min. A negative value means part of the base lifts off the soil; make the base bigger in the direction of the moment.
Too little cover. Concrete cast against the soil needs more cover than concrete cast on blinding; set the exposure to match.
Adding the base weight twice. The engine adds the weight of the base itself (“Auto self-weight” in the results); the loads table takes the column loads only.

7. Where it fits

The column loads come from the RC column calculator or the beam reactions. On the project board a column drawn over a footing passes its load down when you save.

8. Learn more

Try it nowThe calculator opens with the walk-through inputs above. The result is free; sign in for the checks, calc sheet and schedule.
Open the pad footing calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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