Quantity Takeoff Calculator
Material quantities from plan dimensions and specifications.
About this calculator
Element Type quietly changes what Depth/Thickness (in) MEANS, not just how it's used. For a slab or footing (Element Type 0), Depth/Thickness is exactly what it sounds like -- the pour thickness -- and Width (ft) is the plan width, so Length x Width x Depth gives a sensible slab volume. Switch to a wall (Element Type 1) and Depth/Thickness becomes the wall's HEIGHT instead (it drives both the vertical rebar length and the formwork area, which only make sense as a height); the calculator uses a separate Wall Thickness (ft) field for the wall's actual thickness in that mode, since a wall's thickness is a fundamentally different scale of number (typically a fraction of a foot) than a slab's plan width (typically tens of feet or more) -- one shared field with one shared valid range could not honestly represent both. Width (ft) itself is simply ignored in wall mode.
Unit Cost Per CY never touches quantities themselves: Net Concrete Volume, Rebar Weight, and Formwork Area are all inert against Unit Cost Per CY across its full 0-1000 declared range, since cost only multiplies the already-finalized Order Volume at the very end. Waste Factor is different -- it DOES touch quantities, not just cost: it scales both Order Volume and Rebar Weight directly (0% waste gives 14.81 CY / 1,108.9 lbs at default inputs; 30% waste gives 19.26 CY / 1,441.5 lbs), so it's Unit Cost Per CY alone that stays purely a pricing multiplier. Rebar Spacing never enters Formwork Area at all -- rebar and formwork are computed from entirely separate geometry (rebar from spacing and bar count, formwork from perimeter or face area and depth), so tightening rebar spacing changes Rebar Weight without moving Formwork Area by any amount, in either element mode.
Inputs
Results
Order Volume (CY)
15.56
Rebar Weight (lbs)
1,164.3
How to Use This Calculator
- Enter the element length in feet and the depth/thickness in inches from the structural drawings -- for a wall, Depth/Thickness is the wall's HEIGHT, not its thickness.
- Select the element type: 0 for a horizontal slab or footing, 1 for a vertical wall. This determines which width field is used.
- For a slab or footing, enter the plan Width in feet. For a wall, enter the wall's actual Thickness in feet in the separate Wall Thickness field (e.g. 0.67 ft for an 8 in wall) -- the Width field is ignored in wall mode.
- Enter the rebar size (#3–#11) and center-to-center spacing in inches.
- Set the waste factor percentage (typically 3–10%) and the concrete unit price per cubic yard -- waste factor scales quantities directly, while unit cost only affects the price.
- Read the concrete order volume in CY with waste included, total rebar linear feet and weight in lbs, formwork area in SF, and concrete material cost.
How the result changes with Length (ft)
| Length (ft) | Order Volume (CY) | Rebar Weight (lbs) |
|---|---|---|
| 20 | 7.78 | 589.2 |
| 30 | 11.67 | 876.8 |
| 60 | 23.33 | 1,739.5 |
| 100 | 38.89 | 2,889.8 |
What each input means
- Length (ft)
- Element length in feet.
- Width (ft)
- Slab/footing plan width in feet. Ignored in Wall mode (Element Type = 1) -- use the separate Wall Thickness field instead.
- Wall Thickness (ft)
- Wall thickness in feet, used only in Wall mode (Element Type = 1) -- e.g. 0.67 ft for an 8 in wall. Ignored in Slab/Footing mode. Concrete volume multiplies Length x this field x Depth/Thickness for walls.
- Depth / Thickness (in)
- Slab: thickness in inches. Wall: this field is wall HEIGHT in inches, not thickness -- it drives both formwork area and rebar bar counts for walls.
- Rebar Size (#3–#11)
- Rebar bar size number (e.g., #4 = 0.5 inch diameter).
- Rebar Spacing (in o.c.)
- Center-to-center rebar spacing in inches.
- Waste Factor (%)
- Waste allowance for concrete and rebar (typically 3–10%). Scales Order Volume and Rebar Weight directly, not just cost.
- Element Type (0=Slab, 1=Wall)
- 0 = slab or footing (horizontal, uses Width field). 1 = wall (vertical forms on both sides, uses Wall Thickness field instead of Width).
- Concrete Cost ($/CY)
- Ready-mix concrete cost per cubic yard delivered.
What each result means
- Net Concrete Volume (CY)
- Theoretical concrete volume without waste.
- Order Volume (CY)
- Concrete to order, including waste factor.
- Rebar Linear Feet
- Total linear feet of rebar needed.
- Rebar Weight (lbs)
- Total rebar weight including waste.
- Rebar Weight (tons)
- Rebar weight in short tons.
- Formwork Area (SF)
- Square footage of formwork needed.
- Concrete Material Cost ($)
- Ready-mix concrete cost based on order volume.
- Plan Area (SF)
- Slab/footing: true plan area (Length x Width). Wall: Length x Wall Thickness -- the wall's footprint if laid flat, not a wall face area, and a much smaller number than the wall's actual visible surface area.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersLength (ft) = 40, Width (ft) = 20, Depth / Thickness (in) = 6, Rebar Size (#3–#11) = 4 = 8 input(s) provided
- Calculate Order VolumeOrder Volume = netVolumeCY * wasteMultiplier15.56 = 15.56
- Calculate Rebar WeightRebar Weight = totalRebarWeight * wasteMultiplier1164.3 = 1164.3
- Calculate Net Concrete VolumeNet Concrete Volume = netVolumeCF / 2714.81 = 14.81
- Calculate Rebar Linear FeetRebar Linear Feet1660 = 1660
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
For a wall, what should I enter for thickness -- and does the Width field matter?
Use the separate Wall Thickness (ft) field, entered as a decimal -- e.g. 0.67 ft for an 8 in wall. Width (ft) is ignored entirely once Element Type is set to Wall; it only applies to slab/footing plan width. The two fields are kept separate specifically because a wall's thickness and a slab's plan width are different scales of number, and a single shared field can't validate sensibly against both at once.
Why does Depth/Thickness mean something different for a wall than for a slab?
For a slab or footing, Depth/Thickness is the pour thickness, matching its name. For a wall, the same field is used as the wall's HEIGHT instead, since that's what determines both the vertical rebar length and the two-face formwork area -- a wall's actual thickness is entered through the separate Wall Thickness field for that element type, not through Depth/Thickness.
Does raising the concrete unit cost change how much material the takeoff says I need?
No -- Unit Cost Per CY only multiplies the already-computed Order Volume to produce Concrete Material Cost at the very last step. Net Concrete Volume, Order Volume, Rebar Weight, and Formwork Area are all completely unaffected by unit cost across its full 0-1000 declared range.
What waste factor should I actually use for a typical slab pour versus a complex wall form?
Simple flatwork slabs commonly run a 3 to 5 percent waste allowance, while walls with more complex formwork, corners, and rebar congestion often need 8 to 10 percent or more, and every percentage point you enter here adds directly to both Order Volume and Rebar Weight, not merely to the estimated cost.
Why do I need to enter rebar spacing at all if it doesn't change my formwork material order?
Rebar Spacing exists purely to size the reinforcement mat -- how many bars fit across the element and how many linear feet of steel that requires -- since formwork is a separate structural system built from perimeter or face area and depth alone; entering an accurate spacing still matters for getting the rebar order right, even though it never moves the panel or lumber quantity implied by Formwork Area.
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