Reading the results
The three outputs serve different steps of the job: the geometric volume checks the plan quantities, the +10% figure is what to order, and the weight helps with delivery and access planning.
| Result | What it represents | How it is used |
|---|---|---|
| Concrete volume | Exact geometric volume of the specified footing | Quantity check against plans |
| Volume with 10% waste | Geometric volume plus the standard trench-pour allowance | The figure to give the ready-mix supplier |
| Approximate weight | Volume × 2.4 t/m³ (normal-weight concrete) | Truck payloads, site access and load planning |
- Footing size is a structural decision, not an estimating one: width, depth, reinforcement and founding depth are set by the applicable building code (e.g., IRC Chapter 4 for US dwellings) and by soil bearing capacity — this calculator only converts specified dimensions into concrete quantity.
- Trenches poured directly against soil (without forms) typically consume more concrete than the plan dimensions suggest, because of over-excavation and irregular trench walls; the 10% allowance covers typical conditions, but poor soils can require more.
What is a concrete footing?
A footing is the widened base of a foundation that spreads a structure's loads onto the soil. A continuous or strip footing is a long rectangular prism of concrete running under a wall or a line of posts; its volume is simply its length multiplied by its cross-section (width × depth). Footing dimensions — width, depth and the depth of soil cover — are set by the applicable building code and the soil's bearing capacity, with frost depth governing how deep footings must sit in cold climates.
This calculator handles the quantity side of the job: once the footing dimensions are specified on the plans, it converts them into the cubic meters of concrete to order. Trenches cut in soil rarely have perfectly clean sides, so ordering with a waste allowance (10% is the convention used here) is standard practice — over-excavation, sloughing trench walls and uneven trench bottoms all consume extra concrete.
How to use this concrete footing calculator
- Enter the total footing length in meters — for a building perimeter, add up all the footing runs.
- Enter the footing width in centimeters (50 cm is a common residential strip-footing width).
- Enter the footing depth (vertical thickness of the concrete) in centimeters.
- Read the concrete volume, the order volume with 10% waste, and the approximate weight in tonnes.
The formula behind footing volume
The footing volume is length × width × depth, with width and depth converted from centimeters to meters. The order figure adds 10% for waste, and the weight multiplies the geometric volume by 2.4 t/m³, the typical density of normal-weight concrete.
Worked example: a footing run of 10 m at 50 cm wide and 30 cm deep contains 10 × 0.50 × 0.30 = 1.5 m³ of concrete. With 10% waste the order volume is 1.65 m³, and the placed concrete weighs about 1.5 × 2.4 = 3.6 tonnes.
Common mistakes
- Entering width or depth in meters when the field expects centimeters — a 0.5 entry in the width field means 0.5 cm, not 50 cm.
- Measuring footing length wall-by-wall and double-counting the corners where perimeter runs meet — measure the centerline of the footing loop.
- Ordering the exact geometric volume for a trench pour — uneven trench bottoms and sloughing sides routinely consume 5–10% extra concrete.
- Sizing the footing from this calculator — footing width, depth and reinforcement must come from the building code or an engineer's design, based on the loads and soil conditions.
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How much concrete do I need for a 10 meter footing?
A 10 m strip footing that is 50 cm wide and 30 cm deep contains 10 × 0.5 × 0.3 = 1.5 m³ of concrete. With the standard 10% waste allowance, order about 1.65 m³.
How deep should a concrete footing be?
Footing depth is set by the applicable building code and local conditions — footings must bear on suitable soil below the frost line in cold climates, and minimum thickness and width depend on the loads and soil bearing capacity. The IRC provides prescriptive minimums for US dwellings; an engineer designs footings outside prescriptive limits.
Why add 10% waste to a footing pour?
Footing trenches cut in soil have irregular walls and bottoms, and over-excavation is common, so the actual concrete consumed almost always exceeds the plan volume. A 10% allowance is the standard convention for trench pours; formed footings in stable soil may need less.
How much does footing concrete weigh?
Normal-weight concrete weighs about 2.4 tonnes per cubic meter, so a 1.5 m³ footing weighs roughly 3.6 tonnes in place. Reinforced concrete is commonly taken as about 2.5 t/m³.
Does this calculator work for pad footings and post footings?
It computes any rectangular prism, so an individual rectangular pad works by entering its length, width and depth. For round post footings (sonotubes), a post-hole concrete calculator using the cylinder formula is the better tool.
Kaynaklar
- International Code Council (ICC) — International Residential Code (IRC), Chapter 4 (Foundations): prescriptive footing size, depth and frost-protection requirements.
- ACI 332 — Residential Code Requirements for Structural Concrete: residential footing and foundation-wall provisions.
- Portland Cement Association (PCA) — Design and Control of Concrete Mixtures: concrete density and quantity-estimating practice.