Strip footing concrete calculator

For a continuous footing or trench with the same width and depth throughout the measured run.

Total run

The total length belonging to the chosen section, measured so corners and junctions are not counted twice.

Width and depth

The dimensions of the concrete cross-section, not the wall above it.

One constant cross-section per calculation. Calculate sections of different sizes separately and combine their required quantities.

• Net concrete, added extra, required volume and net volume per metre or foot of run.

A measured total run, after accounting for junctions.

Cross-section = width × depth. Net = section × run; required = net × 1.10.

For a closed rectangular strip of constant width, multiplying the outside perimeter by the strip width counts the corner areas twice. Use the concrete footprint: outside rectangle minus inside rectangle.

Worked example: outside concrete-face dimensions 8 × 6 m, strip width 0.4 m and concrete depth 0.3 m. Inner dimensions: 7.2 × 5.2 m. Concrete area = 8 × 6 − 7.2 × 5.2 = 10.56 m². Net volume = 10.56 × 0.3 = 3.168 m³.

For this loop, enter 26.4 m as the total run in Pro²: 2 × ((8 − 0.4) + (6 − 0.4)). Keep width 0.4 m and depth 0.3 m. The app multiplies the entered run, width and depth; it does not correct outside dimensions for you. Apply any chosen allowance after the net volume.

This shortcut applies only to a rectangular loop with uniform width and depth, without internal strips. For junctions, changing widths or stepped depths, split the actual concrete into non-overlapping parts. The example checks quantity, not foundation design.

Ready-mix planning uses the required volume and a truck capacity you enter. Bagged mix uses the finished yield of one bag; bag weight alone does not determine it. Whole bags and loads round up. Optional cost uses your price per volume or per bag.

Bag-count example for a separate slab: 0.660 m³ divided by an assumed yield of 0.020 m³ per bag gives 33 bags. This yield is an example input, not a specification for every 40 kg or 50 kg bag. Check the selected product.

Metric and imperial entry are supported. In these examples, lengths are converted to metres before multiplication; displayed volumes are rounded to three decimals. The arithmetic retains the unrounded value.

The extra percentage is a chosen allowance for this estimate. It is not a required building-code value. Geometry estimates quantity; it does not select concrete strength, foundation depth or reinforcement.

There is no automatic corner or intersection deduction. A stepped footing needs separate sections; this is not a bearing-capacity calculation.

Can I enter an outside perimeter?

Only if you have converted it to a run that represents the concrete volume without overlap. The app multiplies the length you supply.

What if the trench is wider in places?

Estimate those regions separately or use a justified measured allowance. A percentage cannot describe their shape.