semku

Concrete calculator

Enter dimensions and quantities to total concrete volume, bags and mix materials.

Piece 1
Shape
Enter the slab's length, width and thickness. Enter the radius from the center to the edge and the column height. Use equal rises and tread depths for solid stairs filled to a level base. Count the equal steps; each tread adds one rise in height. Enter how many identical pieces to include. Choose ft or in; in an ft field, you can enter 12' 6" or 12 ft 6 in in one box.
Total concrete (cu yd)
1.23 cu yd
Total concrete (cu ft)33.33 cu ft
Total concrete (m³)0.94 m³
40 lb bags112
60 lb bags75
80 lb bags56
Bag estimates use typical yield per bag.[1]
Leave blank or enter 0 for no extra concrete.

Cement, sand and gravel

Mix ratio by volume (cement : sand : gravel)
Parts by volume; 1 : 2 : 3 is a typical ratio for concrete.[2]
Weight of one cement bag; 94 lb is a common size.[2]
Weight of one cubic foot of loose cement; a 94 lb sack is defined as 1.0 cu ft.[3]
Enter a dry-volume factor, or leave blank for no adjustment.
Cement bags (94 lb)
6
Cement5.56 cu ft · 522.22 lb
Sand11.11 cu ft · 0.41 cu yd
Gravel16.67 cu ft · 0.62 cu yd

For gravel, sand, soil and mulch volumes, use the Cubic yard calculator.

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.

Cement, sand and gravel use the total concrete volume above, including any extra percentage, multiplied by the dry-volume factor when you enter one. Each material gets its share of the parts; cement weight is cement volume × bulk density, and cement bags are cement weight ÷ bag weight, rounded up to a whole bag. Volumes and weights are rounded once to two decimal places.[2][3]

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] Use Cement, sand and gravel to estimate mix quantities and cement bags.
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.

Manufacturer yield data (PDF)

Yield data checked:

Cement mix sources

[2] Typical concrete proportions by volume: 1 part portland cement, 2 parts sand, 3 parts gravel; cement sold in 94 lb bags.

Manufacturer portland cement data (PDF)

[3] A US sack of portland cement is the amount occupying a bulk volume of 1.0 cu ft, weighing 94 lb.

Sack definition (industry glossary)

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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.