Concrete Calculator
Calculate the volume of concrete needed for slabs, footings, and columns, plus an estimate of premixed bags required, in both US and metric units.
Enter the dimensions of a slab, footing, or column to calculate the concrete volume needed, shown in both US and metric units, along with an estimated bag count.
Weight of one premixed bag — defaults to a common 80 lb US bag. Switch units or enter your own bag's weight, since standard sizes vary by country and brand.
How This Calculator Works
For a rectangular slab or footing, volume equals length × width × thickness. Because thickness is usually given in inches or centimeters while length and width are given in feet or meters, this calculator converts thickness to the same unit before multiplying — a step that's easy to get wrong by hand.
For a round column or tube, volume equals π × radius² × height, where radius is half the diameter. This is the same formula used for cylindrical forms like Sonotube footings, piers, and fence posts.
The volume shown here is the exact geometric volume of the shape you entered. In practice, subgrade is never perfectly level, some mix is lost during placement, and formwork is rarely built to exact dimensions — most contractors order 5–10% more concrete than the calculated volume to avoid running short mid-pour.
Weight is estimated using a typical normal-weight concrete density of about 150 lb per cubic foot (2,400 kg per cubic meter). Bag count divides that total weight by the weight of a single bag — enter your bag's actual size in pounds or kilograms (usually printed on the packaging) for an accurate count, since standard bag sizes vary by country and brand.
Frequently Asked Questions
About this calculator
This calculator finds the volume of concrete needed for a rectangular slab or footing, or a round column or tube, from its dimensions. Results are shown in cubic feet, cubic yards, cubic meters, and liters at once, along with an estimated weight and the number of premixed bags required based on a bag size (in pounds or kilograms) you can adjust to match the product you're using.
- Slabs and footings — Calculate volume from length, width, and thickness for rectangular slabs, footings, and similar poured forms.
- Columns and tubes — Calculate volume from diameter and height for round columns, piers, and post footings.
- Multiple identical pours — Enter a quantity to calculate the total volume for several identical slabs, footings, or columns at once.
- US and metric results together — Every result is shown in cubic feet, cubic yards, cubic meters, and liters simultaneously, regardless of which unit system you entered dimensions in.
- Bag size in lb or kg — Estimate the number of premixed bags needed by entering your bag's weight in pounds or kilograms — defaults to a common 80 lb US bag, but you can switch units or enter any size.