Answer
Estimated Concrete Volume
12.056 cubic yards
325.5 cubic feet
Estimated Weight of Concrete
21.64 tons
Covering 651 sq. ft. at 6" depthChange dimensions
Optional 10% extra concrete
for waste allowance
10% = 1.21 cubic yards
Total Concrete with 10% = 13.26 cubic yards
for waste allowance
10% = 1.21 cubic yards
Total Concrete with 10% = 13.26 cubic yards
Order Size
This order size is considered
Large
Large
How Many Concrete Bags?*
| 722 | 60lb Concrete bags |
| 541 | 80lb Concrete bags |
| 162.8 | Small wheelbarrow loads |
| 81.4 | Large wheelbarrow loads |
Concrete Truck for 31'x21' x6"
x1.21
1.21 Concrete Truck Loads (10 cu/yd Capacity)
Cost Estimate for 31'x21' x6"
Purchasing ready-mix concrete is by far the easiest way to mix concrete for medium to large projects and can even be used on smaller projects as well. We have provided a cost comparison between ready mix and DIY concrete premix bags to give you a rough ballpark estimate.
Bag Cost Estimate
Pre-mixed concrete bags cost on average $3.50 per 80lb bag. Using pre-mixed bags to cover 651 sq ft at a depth of 6", the estimated cost is $1,893.50
$1,893.50
for 541 x 80lb bags
Truck Cost Estimate
Ready-mixed concrete costs on average $108.22 per cubic yard delivered. Using a concrete truck to cover 651 sq ft at a depth of 6", the estimated cost is $1,304.65
7.9 x $17.00 = $134.30
$1,304.65 + $134.30 = $1,438.95
*6 inch pours and under.
**Cost assumes subbase and general prep is done.
Concrete trucks may also charge a "short load" fee for partially filled loads. Short load fees are charged at about $17 for every yard not used on the truck.
So for a 10 cu/yd Truck Load - 2.1 cu/yd concrete = 7.97.9 x $17.00 = $134.30
$1,304.65 + $134.30 = $1,438.95
$1,438.95
Pros Do Everything*
| $3,255.00 | $5.00 sq ft Low End** |
| $3,906.00 | $6.00 sq ft |
| $4,557.00 | $7.00 sq ft |
| $5,208.00 | $8.00 sq ft |
| $6,835.50 | $10.50 sq ft High End*** |
*6 inch pours and under.
**Cost assumes subbase and general prep is done.
Concrete Extras
A well-compacted subbase provides a strong foundation for concrete to lay on. We recommend you contact your nearest concrete supplier for their recommendations on whether you need a subbase, base depth, and rock type.
With a brief look, a 31x21 area at 6 inches deep, you would need approximately 17.12 tons or 12.06 cubic yards of gravel.
Concrete reinforcing is also recommended in high traffic areas and medium to large areas. Wire mesh on average costs $0.56 per sq ft and fiber mesh costs $0.13 per sq ft.
So for your 651 sq ft area, this may roughly cost $364.56 for wire mesh, $1,953.00 for thicker wire rebar mesh and $84.63 for fiber mesh.
*Reinforcing for 10 inch pours and under.How to Calculate Concrete Amount for 31x21 x6"
31 * 21 = 651 sq ft
6 / 12 = 0.5 ft depth
651 * 0.5 = 325.5 cu ft
325.5 / 27 = 12.055555555556
= 12.056 cu/yd
How to Calculate Concrete Weight
12.055555555556 * 3590 = 43279.44 lbs
Density of concrete used 2130 kg/m3or 133 lbs/ft3.
6 / 12 = 0.5 ft depth
651 * 0.5 = 325.5 cu ft
325.5 / 27 = 12.055555555556
= 12.056 cu/yd
How to Calculate Concrete Weight
12.055555555556 * 3590 = 43279.44 lbs
Density of concrete used 2130 kg/m3or 133 lbs/ft3.
31 ft x 21 ft x 6" Concrete Summary
How much concrete do I need for an area of 31 ft x 21 ft x 6" depth? 12.056 cu. yds.
How many concrete bags would I need for a 31 ft x 21 ft x 6" slab? 541 x 80lb Concrete bags.
How much does it cost to pour a 31'x21' x6" slab? Ready-mix costs approx $1,438.95.
How much does it cost to hire a contractor to concrete a 31'x21' x6" slab? A pro costs between $3,255.00 and $6,835.50.
How do you calculate concrete volume? Formula ((width x length) x (depth in inches / 12)) / 27 = total cubic yards. See our how to here
How many concrete bags would I need for a 31 ft x 21 ft x 6" slab? 541 x 80lb Concrete bags.
How much does it cost to pour a 31'x21' x6" slab? Ready-mix costs approx $1,438.95.
How much does it cost to hire a contractor to concrete a 31'x21' x6" slab? A pro costs between $3,255.00 and $6,835.50.
How do you calculate concrete volume? Formula ((width x length) x (depth in inches / 12)) / 27 = total cubic yards. See our how to here
This Page is Calculated for the Following: 31 ft x 21 ft x 6", 31x21x6, 651 sq. ft., 31 x 21, 31x21, 31x21 x6", 31'x21'x6", 31'x21' x6"
This Concrete calculator can be used for a slab, floor, garage, block, wall, driveway, patio, countertop, footings, foundation, pool or basement, and most rectangular areas.
This Concrete calculator can be used for a slab, floor, garage, block, wall, driveway, patio, countertop, footings, foundation, pool or basement, and most rectangular areas.