Start with the right measurement
Concrete ordering is easiest when a pour is split into measurable rectangles. Enter the finished dimensions, repeat the shape with quantity, and add an allowance you can explain rather than hiding it in a rounded result.
How to use this calculator
- 01Length, width, depth: Finished dimensions for one slab, footing, column, or rectangular section.
- 02Quantity: Number of identical sections.
- 03Waste allowance: An explicit percentage for uneven bases, spillage, and ordering practice.
You get calculated volume and planned volume separately, plus converted cubic metres or bag counts where supported. Supplier order units and bag yields are estimates; confirm the product label or dispatch minimum.
Units: Imperial depth is entered in inches while length and width are in feet. Metric dimensions use metres and centimetres as labelled. Never enter inches as feet.
How the calculation works
Volume = length × width × depth × quantity. Planned volume = volume × (1 + waste%).A 10 × 12 ft slab, 4 in thick, is 40 ft³ or 1.48 yd³ before waste.
Worked examples
Slab order
- Convert 4 in depth to 0.333 ft.
- Multiply 10 × 12 × 0.333 = 40 ft³.
- Divide by 27 for 1.48 yd³; add 8% waste for about 1.60 yd³.
Result: Order units depend on the supplier: ready-mix is commonly sold by cubic yard, while bag counts use the selected yield.
Repeated footings
- Enter one 2 ft × 2 ft × 0.75 ft footing.
- Set quantity to 6 for six identical pads.
- Apply the allowance after the six-footing volume is calculated.
Result: The quantity field keeps repeated pads visible and auditable instead of making one oversized rectangle.
How to measure
- 01Measure the finished inside dimensions of the pour.
- 02Take several depth readings where the base is uneven.
- 03Split L-shapes, steps, and columns into non-overlapping rectangles and add them.
Common mistakes to avoid
- Entering inches as feet
- Forgetting repeated footings
- Ordering exactly the theoretical volume
Safety note
Concrete can burn skin and eyes. Wear gloves, boots, eye protection, and follow the ready-mix or bagged-product safety data sheet.
Limits of this estimate
Bag yields are typical planning values—40 lb: 0.30 ft³, 60 lb: 0.45 ft³, 80 lb: 0.60 ft³. Product yield and site conditions vary.
Frequently asked questions
How much waste should I add?
Five to ten percent is a common planning range, but base accuracy, access, and pour shape can change it.
Does this cover irregular shapes?
Split the shape into rectangles and calculate each section.