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Open toolConcrete Calculator
Estimate concrete volume for a rectangular slab from length, width, and thickness. Add an allowance and review cubic yards, feet, and metres.
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How Concrete Calculator works
Slab dimensions produce a base volume, then the allowance increases it.
Thickness in inches is divided by twelve before multiplying by length and width in feet. The base cubic-foot volume is increased by the entered allowance, then converted into cubic yards and cubic metres.
A simple rectangular slab estimate. Account separately for footings, uneven ground, forms, and supplier minimums.
How to use Concrete Calculator
The slab dimensions use feet for length and width, but inches for depth.
Enter slab dimensions and allowance
Enter length and width in feet, thickness in inches, and the extra allowance percentage. Measure a rectangular slab and keep the units distinct. A thickness copied in feet without conversion would use the wrong scale in this form.
Length
Calculate concrete volume with allowance
Select Calculate and read Concrete to order with allowance in cubic yards. The thickness is converted to feet before the slab volume is calculated. The allowance increases that base volume rather than representing a separately measured part of the slab.
1.48 yd³
Review volume units and excluded shapes
Check Cubic feet, Cubic metres, and Without allowance beside the main estimate. The first two use the adjusted volume; Without allowance shows the base slab quantity. Footings, uneven ground, forms, and supplier minimums need separate consideration.
Cubic feet
Estimate concrete for a rectangular slab
The result is most useful when the shape and thickness can be represented by one rectangle.
Estimate a rectangular pad
Use a hypothetical rectangular pad to calculate one slab volume from its dimensions and thickness. Check whether thickened edges or footings are included elsewhere in the project. The page cannot infer them from the rectangle entered.
Compare two slab depths
Keep length, width and allowance unchanged while comparing depth values. This isolates the volume effect of the thickness input. The result is a material quantity calculation and does not determine what thickness a structure should use.
Review the allowance separately
Run the dimensions with zero allowance, then with the allowance you intend to model. The base volume stays visible beside the adjusted amount. This helps distinguish the measured rectangle from the extra quantity assumed in the order estimate.
Concrete volume in cubic yards, feet, and metres
Compare adjusted volume, base volume, and the supporting unit conversions.
The main answer is cubic yards with the entered allowance. Cubic feet and cubic metres refer to the same adjusted volume. Without allowance refers to the original rectangle, so it represents a different quantity basis.
Displayed volumes are rounded. The page does not select supplier delivery increments, minimum orders or bag counts. Compare the estimated quantity with supplier arrangements separately before deciding how to order the material.
Check mixed units and extra shapes
Confirm dimension units and account separately for excluded shapes.
The most common input mismatch is using feet in the depth field or inches in the length fields. Match each value to its printed unit. Keep a dimension sketch with the estimate so the entered rectangle remains clear.
Uneven ground, footings and nonrectangular sections need separate treatment. This calculator does not assess structural requirements or site conditions. Its output is a simple volume estimate for the geometry and allowance supplied.
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Open toolUse Concrete Calculator
Estimate concrete volume for a rectangular slab from length, width, and thickness.
Concrete Calculator: common questions
Answers about using Concrete Calculator and understanding its results.
Why add extra concrete?
An extra allowance helps cover uneven surfaces and handling loss.
Does this include footings?
No. Calculate footings separately and add their volume.
Which result includes the allowance?
The main cubic-yard result and supporting cubic feet and metres include the extra allowance. Without allowance shows the unadjusted slab volume.
Can I use irregular slab shapes?
This form models one rectangular slab. Calculate separate rectangular sections or irregular volumes outside this tool and check their dimensions before ordering.