MATERIALFOREMAN · SHEET C-002 · CONCRETE WORKS
CALC-002 · DRAWING NO. C-002 · REV A

Concrete calculator.

Drafted to scale · cited sources · honest numbers

Size a slab, footing, round column, or a whole job of mixed pours. Enter dimensions and get cubic yards, 80 lb bag count, ready-mix truck loads, and a delivered-cost range from national-baseline pricing. Add pours and the calculator sums them, then rounds once at the total.

◈ DRAFTING PANEL · CONCRETE TAKEOFF · N.T.S. SHEET C-002 · REV A
Redline · scope notice Materials volume only. Does not size reinforcement, evaluate subgrade or frost depth, or check structural loads. Load-bearing footings and columns require engineered design. Verify with ACI 332 or a licensed engineer before any structural pour.
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Note 01 · Field Procedure

How to measure each pour

  1. Pick the shape for each pour. Slab and footing are length times width times thickness. Round columns and sonotubes are diameter times height. Square columns are width times depth times height.
  2. Measure slab length and width in feet, inside the forms. Measure thickness in inches, from the top of the compacted gravel base to the top of the form board.
  3. For a round column, measure the tube diameter in inches and the finished height in feet. For a footing, the depth is the inches value and the length runs in feet.
  4. Break the job into pours. A slab on four pier footings is five pours: run the slab as one, each footing as its own, and let the calculator sum them.
  5. Check the subgrade for a crown. If the middle dips, add half an inch to slab thickness. The crown is the top reason a DIY pour runs short.
  6. Round once, at the job total. The calculator adds every pour first, then applies waste, so stacking pours never over-orders.
Note 02 · Equation

The formula

yd³  =  ( Σ V )  ÷  27  ×  ( 1 + waste ÷ 100 )
V (slab)L × W × (T ÷ 12); length and width in feet, thickness in inches
V (round)π × (diameter ÷ 24)² × height
V (square)(W ÷ 12) × (D ÷ 12) × height
27cubic feet per cubic yard
Bag count uses 0.6 ft³ per 80 lb bag, Quikrete DS 1101. Waste applies once to the summed volume, never per pour.
Note 03 · Sanity Ranges

Typical pours

T Use case Notes
4"Slab: patio, shed, garage floorNon-structural, light foot and car traffic.
6"Slab: residential drivewayPassenger cars. Rebar or wire mesh required.
8" diaRound: deck post footingSonotube. Height runs to local frost depth.
12" diaRound: porch pier, structuralLoad-bearing. Engineer-designed and permitted.
Note 04 · References

Sources

Authorities cited on this sheet
  1. ACI 332-20: Residential Code Requirements for Structural Concrete · American Concrete Institute. Minimum thicknesses, reinforcement schedules, and aspect-ratio limits for residential concrete. The ACI store page is the canonical link.
  2. Quikrete 80 lb Concrete Mix Technical Data Sheet (DS 1101) · Yield 0.6 ft³ per 80 lb bag, the basis for the bag-count line on the spec slip.
  3. IRC R403.1.4 Footing Depth and Frost Protection · 2021 International Residential Code, free public viewer at ICC. Footings must bear below the local frost line; the depth is the regional variable that sets column and footing height.
  4. NRMCA Concrete in Practice information series · National Ready Mixed Concrete Association reference library on ready-mix delivery, truck capacity, short-load fees, and pour preparation.
Note 05 · Field Manual

What the sheet count does not tell you

A 24 by 24 garage slab, worked out

Take a two-car garage slab: 24 feet by 24 feet, poured 4 inches thick. That is 576 square feet of plan area. Multiply by the thickness in feet (4 inches is 0.333 feet) and the raw volume is 192 cubic feet, or 7.1 cubic yards. Add the 10 percent waste the trade orders by default and you land at 7.8 yards. One ready-mix truck covers it with room to spare.

The same slab in 80 lb bags runs 352 bags. That number ends the bag-versus-truck debate on anything this size. Nobody hand-mixes 352 bags. The bag line on the spec slip earns its place on the small pours where it is a real choice, not on the slab.

Bags or ready-mix, and where the line sits

The crossover is about one cubic yard. Below it, bagged concrete wins on price and hassle: no short-load fee, no truck to schedule, mix what you need. A cubic yard is roughly 45 bags of 80 lb mix, and mixing 45 bags by hand is a long, ugly day. Most crews rent a tow-behind mixer past half a yard.

Above a yard, ready-mix takes over. Plants set a minimum, usually 1 to 3 yards, and charge a short-load fee below it, commonly $50 to $150. If the job lands at 2 yards, price both: the truck plus the short-load fee against the bag count plus a mixer rental. The calculator flags the threshold so the math is not a surprise at the plant.

Footings and columns: frost depth runs the height

A round column or a pier footing is sized by the load above it and the frost line below it. Diameter comes from the structure; height comes from your local frost depth. Footings have to bear on soil below the frost line or they heave. In northern Minnesota that is 60 inches or more; on the Gulf Coast it can be zero. Your building department publishes the local number, and IRC R403.1.4 is the section that requires it.

This calculator sizes the concrete volume for a column or footing you have already specified. It does not size the footing for a load. Anything holding up a roof, a beam, or a deck ledger is engineered work. Get the dimensions from a stamped drawing or your inspector, then come back here for the yardage.

Run the whole job as one takeoff

A real pour is rarely one shape. A slab sits on a thickened edge or on pier footings; a porch has a slab and three columns. Running the calculator once per piece and rounding each up to the next bag or the next quarter-yard over-orders every time. Stack the pours instead. Add each shape, let the calculator sum the volume, and round once at the bottom. The difference on a five-pour job is most of a wasted bag pallet or a half-yard of mud you are paying to haul off.

Note 06 · Common Questions

Common questions

How much concrete do I need?
Measure each pour, enter it above, and the calculator returns cubic yards, 80 lb bag count, and ready-mix truck loads. A 24 by 24 by 4 inch slab needs about 7.8 cubic yards with 10 percent waste. For anything structural, get the dimensions from a stamped drawing first.
How many 80 lb bags of concrete make a cubic yard?
About 45. One 80 lb bag yields 0.6 cubic feet per Quikrete DS 1101, and a cubic yard is 27 cubic feet, so 27 divided by 0.6 is 45 bags. A 60 lb bag yields 0.45 cubic feet, which works out to 60 bags per yard.
How many yards of concrete fit in a truck?
A full ready-mix truck carries up to about 10 cubic yards. Most plants set a 1 to 3 yard minimum and add a short-load fee, commonly $50 to $150, on smaller deliveries.
Is it cheaper to use bags or order ready-mix?
Under about a cubic yard, bags win on price and hassle. Over a yard, ready-mix is cheaper per yard and far less work, even with the short-load fee on small loads. The crossover sits around one yard, roughly 45 bags of 80 lb mix.
PROJ MATERIALFOREMAN
SHT C-002 / 014
REV A · 2026-06-06
DRAWN MF