Concrete Calculator estimates how much concrete a slab, footing or column needs, in cubic yards and cubic meters, plus how many premixed bags to buy. Pick a shape, enter its dimensions in US units (feet and inches) or metric (meters and centimeters), and set a quantity for multiple identical pours — say, four footings or six deck-post columns. The tool converts everything internally and works out volume with the right formula for each shape, including π × r² × h for a round column. It then divides that volume by a typical 60 lb or 80 lb bag yield and rounds up so you know how many bags to load. It is built for DIYers pouring a patio or fence-post footings, and for contractors sanity-checking a takeoff before ordering ready-mix or bagged concrete. Every calculation runs locally in your browser.
Features
Slab, footing and column modes with the correct volume formula for each shape
Switch between US units (feet/inches) and metric (meters/centimeters) with one toggle
Quantity field multiplies volume for several identical slabs, footings or columns
Results in both cubic yards and cubic meters side by side
60 lb and 80 lb bag counts calculated from standard bag yields and rounded up
Column volume uses π × r² × h for accurate cylindrical estimates
One-click copy of a plain-text summary of every result
Runs entirely in your browser — no project dimensions are uploaded
How to use the Concrete Calculator
Choose Slab, Footing or Column
Pick US or Metric units
Enter the shape's dimensions and how many identical pours you need
Read the cubic yards, cubic meters and bag counts, then copy the summary
Example
Input
Slab, 10 ft x 10 ft, 4 in thick, quantity 1
Output
1.23 cu yd (0.94 m³) — about 75 x 60 lb bags or 56 x 80 lb bags
10x10 ft at 4 in thickness = 33.33 cu ft, divided by a 27 cu ft cubic yard.
Common errors & troubleshooting
Slab thickness entered as 4 (feet) instead of 4 inches, giving a wildly oversized volume. — In US mode, thickness and depth fields are inches, not feet — a typical slab is 4 to 6 inches thick, not 4 to 6 feet.
Column result looks too small compared to a rectangular estimate. — Columns use π x r² x h, not width x height — a 12 in diameter column has only about a 0.79 sq ft cross-section, far less than a 1 ft square post.
Bought exactly the calculated number of bags and ran short. — The Concrete Calculator gives a baseline estimate — always add 5-10% for waste, spillage and uneven subgrade before ordering.
Not sure whether to buy 60 lb or 80 lb bags. — 80 lb bags yield more concrete per bag (about 0.6 cu ft vs 0.45 cu ft) so fewer bags are needed, but each bag is heavier to carry and mix.
Frequently asked questions
How does the Concrete Calculator estimate cubic yards?
It multiplies length x width x thickness for a slab or footing, or uses π x r² x height for a column, converts the result to cubic feet, then divides by 27 to get cubic yards.
Does the Concrete Calculator support metric measurements?
Yes. Toggle to Metric to enter large dimensions in meters and thickness or diameter in centimeters — the tool converts everything internally before computing volume.
How accurate are the bag counts from the Concrete Calculator?
Bag counts are based on typical yields of about 0.45 cubic feet for a 60 lb bag and 0.6 cubic feet for an 80 lb bag, rounded up to the next whole bag. Actual yield varies by brand and mix, so treat this as an estimate and confirm with your supplier before ordering.
Can the Concrete Calculator handle multiple footings or columns at once?
Yes. Set the quantity field to the number of identical footings, columns or slabs you are pouring and the volume and bag counts scale automatically.
What is the difference between a footing and a slab in this calculator?
Both use length x width x depth, but a footing is typically entered as a narrow strip (e.g. width and depth in inches) while a slab is a broad, thin pour with thickness in inches — pick whichever mode matches your project.
Is my project data sent anywhere when I use the Concrete Calculator?
No. All dimensions and results stay in your browser and are never uploaded to ArrayKit.
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