Concrete Calculator

How much concrete do I need? Pick a shape, enter dimensions, get yards, bags and cost.

Project Details
Enter your measurements and requirements
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Results
Calculated estimates for your project
Concrete needed1.36 cu yd (36.7 cu ft, 1.04 m³)
Premix bags62 x 80 lb, 82 x 60 lb, 98 x 50 lb or 123 x 40 lb
Ready-mix order1.50 cu yd (rounded up to the next 1/4 yd). A short-load fee likely applies below the plant minimum
WeightAbout 5,500 lb
Bagged cost$403
Ready-mix cost$423 incl. delivery and short-load fee
Cheaper optionBags, by $20. Mixing 62 bags is a lot of work past about 1 yd.

How much to buy

Low, 5% waste
59 bags or 1.50 yd
Typical, 10% waste
62 bags or 1.50 yd
High, 15% waste
64 bags or 1.50 yd

Formula: 33.3 cu ft / 27 = 1.23 cu yd, plus 10% waste. Bags at 0.6 cu ft per 80 lb.

  • Ready-mix rounds up to the next 1/4 yard.
  • Waste covers spillage and an uneven base.

Turn these numbers into a build plan.

  • 10 x 10 ft slab
  • 1.23 yd³ volume
  • 1.5 yd order
Materials List
Recommended materials and quantities
Concrete62 bags, 80 lb

Irregular patio or driveway? Draw it in the concrete slab calculator. Mixing by hand? The concrete mix calculator gives cement, sand, gravel and water.

Next you will need

Footing Rebar CalculatorConcrete Mix CalculatorGravel Calculator (Tons and Cubic Yards)

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Project plan · built from your numbers

Concrete slab, 10 x 10 ft

A 100 sq ft slab poured 4 in thick: 1.23 cubic yards of concrete (order 1.5 yd with 10% extra). Covers base prep, forms, reinforcement, finishing, and curing.

Materials
$514
Time
1 weekend
Level
Intermediate
8 steps 9 tools 7 materials
  1. 1

    Plan, locate, and permit

    Call 811 for utility locates. Many towns want a permit for slabs that support a structure or sit near a property line, so check before ordering concrete.

    • 811 utility locate
    • Check permit needs
    • Plan slope away from buildings, 1/8 in per ft
  2. 2

    Excavate and compact the base

    Dig out 10 x 10 ft to 8 in below finished height. Add 4 in of gravel (1.23 yd³) and compact in two lifts.

    • Remove sod and soft soil
    • Spread gravel in 2 in lifts
    • Compact each lift
  3. 3

    Build the forms

    Set 6 form boards around the 40 ft perimeter on stakes every 3 ft. Square them by matching diagonals and set the slope with a string line.

    • Diagonals equal
    • Stakes outside the forms, below the top edge
    • Slope set for drainage
01 · Your numbers
Slab
10 x 10 ft
Volume
1.23 yd³
Order
1.5 yd
Est. cost
$514
02 · The plan

8 steps · 9 tools · 7 materials

5 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

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Concrete slab, 10 x 10 ft

Finished in 1 weekend · $514 DIY

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Borrow these 9 tools from neighborsFull how-to guide: Pour a concrete slab

How to calculate concrete

The formula is V = L x W x D / 27, with every dimension in feet, for cubic yards. Round shapes use 3.14 x radius² x depth instead.

  1. Measure in feet. Measure the length and width in feet and the thickness in inches. Divide the inches by 12: 4 in is 0.333 ft.
  2. Multiply for cubic feet. Volume = length x width x thickness. A 10 x 10 ft slab at 4 in is 10 x 10 x 0.333 = 33.3 cu ft.
  3. Divide by 27 for cubic yards. There are 27 cu ft in a cubic yard, so 33.3 / 27 = 1.23 cu yd.
  4. Add waste and convert to bags. Add 5 to 10% for spillage and uneven ground, then divide cubic feet by 0.60 for 80 lb bags or 0.45 for 60 lb bags (56 x 80 lb before waste).
Worked exampleVolume80 lb bags60 lb bags
10 x 10 ft slab, 4 in thick1.23 cu yd5675
Twelve 12 in tubes, 4 ft deep1.40 cu yd6384

Concrete reference tables

Recommended thickness and strength by use
UseThicknessTypical PSI
Sidewalk, walkway4 in2,500 to 3,000
Patio, shed floor4 in3,000
Garage floor4 to 5 in3,500
Driveway (cars)5 to 6 in4,000
RV pad, heavy trucks6 to 8 in4,000+
Footing8 to 12 in2,500 to 3,000
Cubic yards per 100 sq ft
ThicknessCubic yards80 lb bags
4 in1.2356
5 in1.5470
6 in1.8584
8 in2.47112
Bags per cubic yard
Bag sizeYieldBags per yard
40 lb0.30 cu ft90
50 lb0.38 cu ft72
60 lb0.45 cu ft60
80 lb0.60 cu ft45

Bags or ready-mix?

Bagged premix costs more per yard but has no delivery or minimum. Ready-mix plants often charge a short-load fee under 3 to 5 yards, so the crossover sits near 1 cubic yard. Order ready-mix rounded up to the next quarter yard; running short mid-pour leaves a cold joint.

Concrete calculators by project

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Concrete calculator FAQ

How much concrete do I need for a 10x10 slab?

A 10 x 10 ft slab 4 in thick is 1.23 cubic yards (33.3 cu ft), about 56 bags of 80 lb before waste. At 6 in thick it is 1.85 cubic yards.

How many bags of concrete make a yard?

About 45 bags of 80 lb, 60 bags of 60 lb, 72 bags of 50 lb or 90 bags of 40 lb. An 80 lb bag yields roughly 0.60 cubic feet.

How do I calculate concrete for stairs?

Each step is a block: width x tread depth x its height above the ground. Add them up (or use width x run x rise x n(n+1)/2), add the top landing, then convert to yards. Three 7 x 11 in steps 4 ft wide take about 0.48 cubic yards. The concrete steps calculator also handles landings and gravel fill.

How much concrete for a sonotube?

A 12 in tube holds 0.785 cu ft per foot of depth, so a 4 ft tube is 3.1 cu ft, about 6 bags of 80 lb. Twelve of them is 1.40 cubic yards (63 bags).

How much gravel goes under a slab?

Most slabs sit on 4 in of compacted crushed stone, 6 in for driveways or soft soil. For a 10 x 10 slab that is about 1.2 cubic yards of base, or roughly 1.7 tons.

What is a monolithic slab?

A slab and its perimeter footing poured in one piece, with the edge thickened to 12 in or more. Choose "Thickened edge" on the slab shape to add the footing volume, or use the concrete slab calculator for a full plan.

Should I use ready-mix or bagged concrete?

Bags win for small pours under about 1 cubic yard. Above that, ready-mix is usually cheaper and far less work, even with a short-load fee. The calculator compares both at your prices.

How long does concrete take to cure?

Walk on it after 24 to 48 hours, drive light vehicles on it after 7 days, and it reaches design strength at 28 days. Keep it damp or covered for the first week.

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