Calculate the concrete volume required for isolated, rectangular, or square footings.
How to Use the Footing Calculator
Choose the footing type — for a square footing, width is set equal to length automatically.
Enter length, width, and depth in feet, plus the number of identical footings.
Click "Calculate" to see the concrete volume per footing and in total.
Worked Example: Footings for a Small House
Suppose the drawing shows 12 square footings, each 5 ft × 5 ft with a 1 ft thick slab. Choose "Square", enter 5 for length, 1 for depth and 12 for the number. Each footing is 5 × 5 × 1 = 25.00 cu.ft and the total is 300.00 cu.ft, or about 8.50 m³ after dividing by 35.315.
All dimensions here are in feet, unlike the beam and column calculators where the cross-section is entered in inches. A 15-inch thick footing should be entered as 1.25, not 15.
Remember the PCC Bed
Reinforced footings are normally cast on a thin layer of plain cement concrete (PCC), a lean mix that gives a clean, level base and keeps the steel off the soil. The bed is usually a few inches thick and extends a little beyond the footing on every side. Its exact size and mix are given in the drawings.
Calculate it as a second, separate run. For a 3-inch bed projecting 3 inches on each side of a 5 × 5 ft footing, enter 5.5 × 5.5 × 0.25 ft: about 7.56 cu.ft per footing, or 90.75 cu.ft for all twelve. Keep this total apart from the RCC figure because the two use different mixes.
Sloped (Trapezoidal) Footings
This calculator handles footings with straight vertical sides. Many isolated footings have a rectangular base slab topped by a sloping portion that narrows towards the column. For those, work out the two parts separately:
Base slab: length × width × base thickness, which you can get from this calculator.
Sloping part: h ÷ 3 × (A1 + A2 + √(A1 × A2)), where h is the height of the slope, A1 the bottom area and A2 the top area.
Example: a 5 × 5 ft base 0.5 ft thick gives 12.5 cu.ft. Above it, a slope 0.75 ft high tapers to a 1.5 × 1.5 ft top, so A1 = 25, A2 = 2.25 and √(25 × 2.25) = 7.5. The slope holds 0.25 × 34.75 ≈ 8.69 cu.ft, making about 21.19 cu.ft per footing. Treating the whole thing as a 1.25 ft thick block would give 31.25 cu.ft, overestimating by about 10 cu.ft per footing.
Before You Order Concrete
Footing size and depth below ground depend on the load and the soil's bearing capacity, which is why they must come from a structural engineer, ideally after a soil test.
Excavation is larger than the footing. Pits are dug wider to leave working space for formwork and fixing steel, so do not use the concrete volume to estimate digging or earth removal.
Footings of different sizes, which are common where corner columns carry less load than interior ones, should each be calculated as their own group.
The column stub from the top of the footing up to plinth level is not part of this result. Include it with the Column Calculator.
Frequently Asked Questions
Volume per footing (cu.ft) = Length × Width × Depth. For a 5 ft × 5 ft × 1 ft footing, that is 25 cu.ft. Multiply by the number of footings for the total.
A square footing has equal length and width. A rectangular footing has different length and width. "Isolated" describes a single, independent footing under one column (which may itself be square or rectangular) — the volume math is the same either way.
No. Run the calculator a second time with the PCC dimensions, which are usually slightly larger than the footing and only a few inches thick. Keep the two totals separate, because PCC uses a leaner mix than the reinforced footing.
Use this tool for the flat base slab, then add the sloping part using h ÷ 3 × (A1 + A2 + √(A1 × A2)), with A1 and A2 as the bottom and top areas of the slope. Entering the full height as a solid block overstates the concrete.
Divide inches by 12 to get feet. A 12-inch footing is 1 ft, 15 inches is 1.25 ft and 18 inches is 1.5 ft. For metric drawings, 1 metre is about 3.281 ft, so a 450 mm footing is about 1.48 ft.