semkuConcrete calculator
Enter dimensions and quantities to total concrete volume and estimate bags.
Calculation rules
Slab volume is length × width × thickness. Round column volume is π × radius² × height. Solid stairs with equal steps use width × tread depth × rise × steps × (steps + 1) / 2. Multiply each piece by its quantity, then add the volumes; 1 cu yd = 27 cu ft and 1 cu ft = 0.028316846592 m³.
Each bag count is the total volume divided by the typical yield for that bag size, rounded up to a whole bag.[1] Each size is a separate estimate; check the yield on the bags you buy.
Extra concrete is added only at the percentage you enter. No allowance for compaction or site losses is added automatically. Volume displays are rounded once to two decimal places; positive volumes below 0.01 display as <0.01. Bag counts use the unrounded volume, with π approximated to 40 decimal places for round columns.
Frequently asked questions
- How much concrete does a 10 ft by 10 ft slab need at 4 in thick?
- With one slab and no extra concrete, the volume is 1.23 cu yd, 33.33 cu ft or 0.94 m³. The estimated bag counts are 112 of the 40 lb size, 75 of the 60 lb size or 56 of the 80 lb size.[1]
- Can I combine different shapes?
- Yes. Add each slab, round column or set of stairs as a piece, enter its quantity and use the combined total.
- What kind of stairs does this calculate?
- Solid stairs with equal rises and tread depths, filled down to a level base. Landings and hollow spaces are not part of this stair formula.
- Is extra concrete included in the bag counts?
- Yes, when you enter an extra percentage. Leaving it blank or at zero adds none; bag counts are rounded up after the extra volume is included.
Bag yield source
[1] Typical yield per bag: 40 lb ≈ 0.30 cu ft; 60 lb ≈ 0.45 cu ft; 80 lb ≈ 0.60 cu ft.
Yield data checked:
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Calculations run in your browser without sending your calculation inputs or results to the server. See “Privacy on this page” for information about access data.