Calculate footing concrete volume, check a foundation layout is square, and estimate cost — metric or imperial.
Footing type
A common planning range is 5-15%, but the right allowance for your project depends on trench/formwork accuracy and site conditions - it is not a universal figure.
Presets are planning examples only - actual yield varies by manufacturer and mix, so use your bag's stated yield for an accurate count.
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On the Footing Concrete tab, choose strip/continuous (optionally as multiple independent sections), pad/isolated (rectangular or circular), or circular pier/post hole footings, enter your dimensions, and get a net concrete volume, purchase/pour allowance, ordering volume and bag count. On the Squaring tab, check a single corner using the 3-4-5 (Pythagorean) method, or a full rectangle using both diagonals - the calculator shows you the differences without deciding pass or fail, unless you enter your own tolerance. Use the Cost tab with a ready-mix/bulk or bagged concrete price for a material cost estimate.
A strip (continuous) footing's volume is width × depth × length; if your footing isn't a uniform run, you can add multiple independent sections instead, each with its own dimensions, and they're summed together. A rectangular pad footing's volume is width × length × depth × quantity, a circular pad or pier's volume is π × (diameter÷2)² × depth × quantity.
A purchase/pour allowance (5-15% is a common planning range, but not a universal figure) is added on top of this net volume to account for spillage, uneven trench sides and over-excavation, giving an ordering volume. Divide the ordering volume by your concrete's bag yield to get a bag count - bag yield presets are planning examples only, so use your bag's actual stated yield where possible.
A strip (or continuous) footing runs the full length of a wall, spreading its load evenly along the ground beneath it. A pad (or isolated) footing is a single block of concrete supporting one point load, and can be rectangular/square or circular. A circular pier or post hole footing is typically deep and narrow, supporting a single post, deck pier or similar point load. Some foundation designs combine several of these: strip footings under load-bearing walls, pad footings under isolated posts or columns, and piers for decks or fences.
The 3-4-5 method is a practical application of the Pythagorean theorem: if one side from a corner measures 3 units and the adjacent side measures 4 units, the diagonal between their far ends must be exactly 5 units for the corner to be square, because 3² + 4² = 5². This calculator generalises the method to your actual measurements for a single corner, or lets you check a full rectangle using both diagonals - a layout can look square at one corner and still be a skewed parallelogram overall, which comparing both diagonals catches.
The calculator always shows your measured value(s) against the theoretical value, with the signed and absolute difference - it does not decide what counts as "close enough," since that depends on your project's own tolerance requirement. Enter your own tolerance if you'd like an automatic within/outside result.
The Cost tab prices your footing concrete either as bagged concrete (bag count × price per bag) or ready-mix/bulk (ordering volume in m³ or yd³ × price per unit volume) - these two pricing methods are never combined, since you'd only use one supply method for a given pour. Optional delivery/short-load fee, pump cost and other cost lines are added on top only if you enter them. This is a material-only estimate - it doesn't include excavation, formwork, reinforcement (rebar or mesh), vapour barriers, or labour. Get a local contractor quote for full project pricing.
Example 1 — Strip footing. A footing 0.4m wide, 0.3m deep, running 20m total: net volume = 0.4 × 0.3 × 20 = 2.4 m³. With a 10% purchase/pour allowance, that's an additional 0.24 m³, for an ordering volume of 2.64 m³, needing 245 bags of 25kg concrete (at a yield of ~0.0108 m³ per bag).
Example 2 — Foundation squaring. A rectangular layout with sides of 6m and 4m: the theoretical diagonal is √(6² + 4²) = √52 ≈ 7.2111 m. If your measured diagonal is 7.216m, the calculator shows a difference of about +0.005m for you to compare against your own project's tolerance.
A common mistake with footings is forgetting the purchase/pour allowance, which often leaves a project just short of enough concrete for the final section poured. Another is mixing up bagged and ready-mix pricing, or treating a partial ready-mix load the same as a full one without accounting for a short-load fee. For squaring, a frequent error is measuring the diagonal from the wrong reference points, or checking only one corner of a rectangular layout - a layout can be square at one corner but still be a parallelogram rather than a true rectangle, which is why checking both diagonals of the full rectangle is more reliable.
This calculator computes concrete volume from the dimensions you enter and checks diagonal measurements using the Pythagorean theorem - it does not determine footing width, depth, foundation type, or reinforcement (rebar or mesh) requirements for your specific soil bearing capacity, frost depth, structural loads, concrete strength grade, or settlement behaviour. It does not certify structural adequacy or building-code compliance. These must come from your engineered plans, local building code, or a structural engineer. Squareness tolerance (how close is "close enough") depends entirely on your project's specific requirements and is only applied if you enter your own tolerance value.
Multiply width × depth × length for a strip/continuous footing (or sum multiple independent sections), width × length × depth × quantity for rectangular pad footings, or π × (diameter÷2)² × depth × quantity for circular pads or piers. Use the Footing Concrete tab above with your dimensions for an automatic net volume, purchase/pour allowance and bag count.
The 3-4-5 method uses the Pythagorean theorem: if one side of a right angle is 3 units and the other is 4 units, the diagonal (hypotenuse) between their ends must be exactly 5 units for the corner to be a true 90 degrees. Use the Squaring tab above with your actual side lengths to calculate the theoretical diagonal for your foundation.
Measure two adjacent sides of your rectangular layout, then measure the diagonal between their far ends, and compare it to the theoretical diagonal from the Squaring tab above. For a full rectangle check, measure both diagonals - if they match each other and the theoretical value, the layout is a true rectangle. This calculator shows you the differences; it does not decide pass or fail for you unless you enter your own tolerance.
A strip (or continuous) footing is a long, narrow concrete footing that runs beneath a wall, distributing its load along the entire length. This is different from a pad (isolated) footing, which supports a single point load like a post or column.
A pad (or isolated) footing is an individual block of concrete that supports a single point load, such as a post, column or pier, rather than running continuously like a strip footing under a wall. Pads can be rectangular/square or circular.
This depends on your local frost depth, soil bearing capacity, and the load the footing carries - it varies significantly by region and project. Check your local building code or a structural engineer's specification rather than using a generic depth.
This depends heavily on foundation type, size, soil conditions, and local labour/material costs. Use the Cost tab above with your own ready-mix or bagged concrete prices for a material-only estimate specific to your project; get a local contractor quote for full project pricing.
A stem wall foundation has a short concrete wall built on top of a footing, raising the structure above ground level before the floor slab or framing begins - commonly used where additional height, drainage, or termite protection is needed compared to a slab-on-grade foundation.
This depends on the volume needed, site access, and local supplier minimums - ready-mix/bulk delivery is common for larger pours, while bagged concrete suits small footings or hard-to-access sites. The Cost tab above prices each method separately from your ordering volume or bag count - they are never added together.
No - it calculates concrete volume from dimensions you provide and checks a layout's diagonal measurements; it does not determine the footing size, depth or reinforcement your specific soil and structural load require. Get this from your engineered plans, local building code, or a structural engineer.
A square foundation ensures walls meet at true right angles, which is essential for framing, flooring, roofing and finishes to fit correctly - even a small error at the foundation stage compounds throughout the rest of the build.