Concrete / Volume & material cost
Concrete Slab Calculator
Find how much concrete a rectangular slab or pad needs in cubic metres or cubic yards. Add your supplier’s rate for a concrete material estimate.
Estimate your slab or pad concrete
Start with the finished concrete dimensions. Add an allowance and supplier quote if needed.
Concrete dimensions
Use the finished concrete depth; exclude gravel and other sub-base layers.
Blank means 0%. Choose an allowance for your job; no standard percentage is assumed.
Enter your supplier's concrete-only rate. Leave blank for quantities only.
Currency labels do not convert exchange rates or supply local prices.
Concrete quantities
- Total concrete area
- 24 m²
- Net concrete volume
- 2.4 m³
- Net concrete volume in yards
- 3.139081486 yd³
- Allowance volume
- 0 m³
- Estimated ordering volume
- 2.4 m³
- Estimated ordering volume in yards
- 3.139081486 yd³
Concrete material cost
- Estimated material cost
- —
- Material cost per m²
- —
View copyable summary
ConstructGauge — Concrete Slab Calculator length: 6 m width: 4 m thickness: 100 mm Slab or pad count: 1 Total area: 24 m² Net concrete: 2.4 m³ / 3.139081486 yd³ Allowance (0%): 0 m³ Estimated order: 2.4 m³ / 3.139081486 yd³ Uniform rectangular slabs. Excludes labor, delivery, pumping, reinforcement, formwork and preparation. Confirm supplier order increments. Not structural design.
Method
How to calculate concrete for a slab
Measure the slab’s length and width, then enter the thickness specified for your project. Convert all three dimensions to the same length unit before multiplying. For several identical slabs, multiply by their count.
- Total area = length × width × slab count
- Net concrete volume = total area × thickness
- Allowance volume = net volume × allowance percentage ÷ 100
- Estimated ordering volume = net volume + allowance volume
- Concrete material cost = ordering volume × price per matching volume unit
These are rectangular geometry and arithmetic calculations, not structural design rules. The calculator uses metres internally and converts the results for display. One cubic yard is 0.764554857984 cubic metres. Displayed values are rounded; intermediate calculations are not.
Worked example
A 6 m × 4 m slab, 100 mm thick
Convert 100 mm to 0.1 m. The area is 24 m² and the net concrete volume is 2.4 m³. A chosen 5% allowance adds 0.12 m³, giving an estimated order of 2.52 m³.
At an illustrative rate of 150 per m³, the concrete material cost is 378, or 15.75 per m², in the same currency as the quote. This rate is an arithmetic example, not a current local price; 5% is not a prescribed allowance.
Working in feet and inches
A 12 × 12 ft slab at 4 in thick has an area of 144 ft². Its volume is 144 × (4 ÷ 12) = 48 ft³, or 1.777777… yd³. With no allowance and a quote of 180 per yd³, material cost is 320. Switching units converts the same physical slab and supplier rate.
Using the calculator for a concrete pad
A rectangular concrete pad with a uniform thickness uses the same length × width × thickness calculation as a slab. Enter the finished concrete dimensions shown on the project drawings, or measure between the inside faces of the forms. Thickness means the concrete depth; do not include a gravel sub-base or other layers beneath the concrete.
For an L-shaped pad, split the footprint into non-overlapping rectangles and calculate each section separately. Treat thickened edges as separate volumes so the main slab thickness is not counted twice.
Material cost versus installed slab cost
This estimate covers the concrete itself. A contractor’s installed price may also include excavation, sub-base, formwork, reinforcement, labor, pumping, finishing, delivery and taxes. Those items are outside this estimate. Compare quotes on the same basis and confirm minimum loads and order increments with your supplier.
Before requesting prices, use the ready-mix versus bagged concrete guide to prepare comparable quote requests and check access, mixing work and extra charges.
For a quantity schedule, use the net volume as the geometric concrete quantity and keep the ordering allowance separate. A formal BOQ may require additional project-specific measurement rules.
Concrete slab calculator FAQ
Can I use this as a concrete pad calculator?
Yes, for a rectangular pad with a uniform thickness. Enter its finished length, width and concrete depth. This calculates concrete quantity only; it does not choose the pad size, thickness, reinforcement or sub-base.
How much concrete do I need for a 20 × 20 ft slab?
You also need the thickness. At 4 in thick, the net volume is 400 × (4 ÷ 12) ÷ 27, approximately 4.9383 yd³. This is a quantity example, not a thickness recommendation.
What is the slab cost per square foot or square metre?
Enter your supplier’s price per cubic yard or cubic metre. The calculator divides the estimated material cost, including any volume allowance, by total slab area. This is not an installed-price estimate.
What waste percentage should I enter?
Choose it for your site conditions and ordering plan. Uneven formation, handling losses and measurement uncertainty can affect the order. The default is zero so no allowance is added without your input.
Can I calculate irregular slabs or thickened edges?
This version assumes identical rectangular slabs with uniform thickness. Calculate distinct rectangular sections separately without overlapping them. Thickened edges, openings and other shapes need separate measurements.
Does the currency selector provide US, Australian or UK prices?
No. It labels the rate you enter and the resulting cost. It does not fetch regional prices or convert currencies.
Does this calculate cement bags or reinforcement?
No. Concrete volume alone does not establish bag counts without a product yield, or reinforcement without a design. Use the product specification and project drawings for those quantities.
Calculation basis and source limits
The method derives from rectangular geometry, percentage allowance, and unit-price arithmetic. It does not select a structural thickness, concrete grade, or mix design. Confirm those inputs from your project specification.
Unit conversions use international feet, inches, and yards. See NIST’s SI conversion-factor reference for the conversion basis; it does not certify this calculator or its construction assumptions.