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    Concrete Needed for a 3 × 3 feet Slab 4 inches Thick

    Concrete Calculator
    Pour a slab of
    ft
     ×
    ft
    and a thickness of
    in

    How much concrete do I need for a 3 × 3 feet slab?

    Answer

    Pouring a 3 × 3 feet slab 4 inches thick takes
    0.11 cubic yards

    That is 3 cubic feet, or 5 bags of 80 lbs dry mix. Ordering ready mixed instead, ask for 0.13 cubic yards — the 10% NRMCA advises on top of the plan volume.

    How the Volume Is Worked Out

    Cubic yards = width × length × inches ÷ 324

    The 324 is exact, not a fudge factor: a cubic yard is 27 cubic feet, so spread one inch thick it covers 27 × 12 = 324 square feet. No density is involved, which is why the volume is the part of this answer that is exact — the weight further down is not.

    3 × 3 feet = 9 square feet

    9 square feet × 4 inches

    ≈

    0.11 cubic yards

    (= 3 cubic feet)

    Bags or a Mixer

    Bags and ready mixed concrete are two ways to buy the same volume, and this page prints both. A bag of 80 lbs yields 0.6 cubic feet, so this slab is 5 bags — 400 lbs of dry mix to carry, mix and place before it starts to set.

    Part bags are rounded up, always. Half a bag cannot be bought, and running one bag short in the middle of a pour is worse than a wasted trip: the fresh concrete sets against the concrete already down and leaves a cold joint. One cubic yard takes 45 bags, and a truck mixer holds 8–12 cubic yards (NRMCA, Concrete in Practice, CIP 31) — which is where bags stop making sense.

    3 × 3 feet at Other Thicknesses

    Thickness is an input, and every row below is a page of its own — set it in the form or follow a link. A footpath, a patio or a shed floor is normally 4 inches; a slab a car stands on goes 5 to 6 inches over a compacted base.

    Thickness Concrete Cubic feet Bags Weight
    3 inches0.0833 cubic yards2.25 cubic feet4 bags315 lbs
    4 inches0.11 cubic yards3 cubic feet5 bags416 lbs
    5 inches0.14 cubic yards3.75 cubic feet7 bags529 lbs
    6 inches0.17 cubic yards4.5 cubic feet8 bags643 lbs
    8 inches0.22 cubic yards6 cubic feet10 bags832 lbs

    What This Much Concrete Weighs

    0.11 cubic yards of concrete weighs about 416 lbs — 0.21 tons — at 3,780 lbs per cubic yard. That figure is the unit weight the QUIKRETE Concrete Mix data sheet (Product No. 1101, revised October 2022, Table 1) gives as 140 lbs per cubic foot, measured to ASTM C138.

    One number, not a range — and that is what the source gives. The data sheet says «approximately», so this is a nominal, not a measurement of your mix. Three limits come with it: it is ordinary normal-weight concrete on dense aggregate, so lightweight mixes weigh far less and reinforcement adds the weight of the steel; it is the density of the fresh placed concrete, not of the dry bag; and it belongs to one packaged product, so ready mixed concrete of another recipe lands near it rather than on it.

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    How Much Concrete for a 3 × 3 ft Slab?. A 3 × 3 feet slab 4 inches thick is 9 square feet and takes 0.11 cubic yards of concrete — 5 bags of 80 lbs.
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    Concrete by Slab Size at 4 inches Thick

    SlabConcrete neededCubic feetBags of dry mix
    2 × 2 feet0.0494 cubic yards1.33 cubic feet3 bags
    2 × 3 feet0.0741 cubic yards2 cubic feet4 bags
    2 × 4 feet0.0988 cubic yards2.67 cubic feet5 bags
    3 × 3 feet0.11 cubic yards3 cubic feet5 bags
    4 × 4 feet0.2 cubic yards5.33 cubic feet9 bags
    4 × 6 feet0.3 cubic yards8 cubic feet14 bags
    4 × 8 feet0.4 cubic yards10.67 cubic feet18 bags
    6 × 6 feet0.44 cubic yards12 cubic feet20 bags
    6 × 8 feet0.59 cubic yards16 cubic feet27 bags
    8 × 8 feet0.79 cubic yards21.33 cubic feet36 bags
    8 × 10 feet0.99 cubic yards26.67 cubic feet45 bags
    8 × 12 feet1.19 cubic yards32 cubic feet54 bags
    10 × 10 feet1.23 cubic yards33.33 cubic feet56 bags
    10 × 12 feet1.48 cubic yards40 cubic feet67 bags
    10 × 14 feet1.73 cubic yards46.67 cubic feet78 bags
    10 × 15 feet1.85 cubic yards50 cubic feet84 bags
    10 × 16 feet1.98 cubic yards53.33 cubic feet89 bags
    10 × 20 feet2.47 cubic yards66.67 cubic feet112 bags
    12 × 12 feet1.78 cubic yards48 cubic feet80 bags
    12 × 16 feet2.37 cubic yards64 cubic feet107 bags
    12 × 20 feet2.96 cubic yards80 cubic feet134 bags
    12 × 24 feet3.56 cubic yards96 cubic feet160 bags
    14 × 14 feet2.42 cubic yards65.33 cubic feet109 bags
    15 × 15 feet2.78 cubic yards75 cubic feet125 bags
    15 × 20 feet3.7 cubic yards100 cubic feet167 bags
    16 × 16 feet3.16 cubic yards85.33 cubic feet143 bags
    16 × 20 feet3.95 cubic yards106.67 cubic feet178 bags
    16 × 24 feet4.74 cubic yards128 cubic feet214 bags
    20 × 20 feet4.94 cubic yards133.33 cubic feet223 bags
    20 × 30 feet7.41 cubic yards200 cubic feet334 bags
    20 × 40 feet9.88 cubic yards266.67 cubic feet445 bags
    24 × 24 feet7.11 cubic yards192 cubic feet320 bags
    24 × 30 feet8.89 cubic yards240 cubic feet400 bags
    25 × 25 feet7.72 cubic yards208.33 cubic feet348 bags
    30 × 30 feet11.11 cubic yards300 cubic feet500 bags
    30 × 40 feet14.81 cubic yards400 cubic feet667 bags
    30 × 50 feet18.52 cubic yards500 cubic feet834 bags
    30 × 60 feet22.22 cubic yards600 cubic feet1,000 bags
    36 × 36 feet16 cubic yards432 cubic feet720 bags
    40 × 40 feet19.75 cubic yards533.33 cubic feet889 bags
    40 × 50 feet24.69 cubic yards666.67 cubic feet1,112 bags
    40 × 60 feet29.63 cubic yards800 cubic feet1,334 bags

    Concrete Calculator

    This calculator works out how much concrete a slab needs: enter the two sides and the thickness and it returns the volume in cubic yards and cubic feet, the number of 80 lbs bags of dry mix, what the finished slab weighs and how much ground one cubic yard covers. For example, it can help you find out how much concrete do I need for a 3 × 3 feet slab? (The answer is: 0.11 cubic yards). Enter the sides (e.g. 3 × 3 feet), choose the unit and set the thickness — 4 inches by default, anything from 1–24 inches is accepted and gets its own page.
    Concrete Calculator
    Pour a slab of
    ft
     ×
    ft
    and a thickness of
    in

    FAQ

    How much concrete do I need for a 3 × 3 feet slab?

    Pouring a 3 × 3 feet slab 4 inches thick takes 0.11 cubic yards

    How many bags of concrete for a 3 × 3 feet slab?

    5 bags of 80 lbs: the slab is 3 cubic feet and one bag yields 0.6 cubic feet. Part bags are rounded up, because running one bag short mid-pour leaves a cold joint. That is 400 lbs of dry mix to carry and mix; a truck mixer holds 8–12 cubic yards.

    How much does a 3 × 3 feet concrete slab weigh?

    About 416 lbs — 0.21 tons. 0.11 cubic yards at 3,780 lbs per cubic yard, the nominal unit weight the QUIKRETE Concrete Mix data sheet gives for that mix, measured to ASTM C138 (140 lbs per cubic foot). It is one product's figure, not a norm for concrete as a category: structural lightweight runs well under it, and reinforcement adds the weight of the steel.

    How much concrete should I order for a 3 × 3 feet slab?

    Order 0.13 cubic yards rather than 0.11 cubic yards. NRMCA advises 4% to 10% over the volume calculated from plan dimensions, for waste, over-excavation and settlement (Concrete in Practice, CIP 31); this is the top of that band.

    How much area does one cubic yard of concrete cover at 4 inches?

    81 square feet, because a cubic yard spread one inch thick covers 324 square feet. Divide 324 by the depth in inches to get the coverage at any other thickness.

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