By the MassBid Estimation team · Reviewed by a senior estimator with 10+ years of experience · Published · Updated
In short
To estimate concrete, measure each footing, wall, column, beam and slab from the structural drawings, multiply length × width × thickness in feet to get cubic feet, and divide by 27 to get cubic yards. A 4 inch slab takes 1 cubic yard per 81 square feet. Add 4 to 10 percent for waste, uneven subgrade and form deflection, then take off the rebar in pounds, the formwork in square feet of contact area, and the finishing, vapor barrier and joints before pricing labor and material.
- Volume formula
- Length × width × thickness (ft) ÷ 27 = cubic yards
- 4 in. slab
- 81 sq ft per cubic yard
- 6 in. slab
- 54 sq ft per cubic yard
- Waste allowance
- 4 to 10% over plan dimensions (NRMCA)
- 80 lb bag
- About 0.60 cu ft, so 45 bags per cubic yard
- Formwork
- Square feet of contact area (SFCA)
- CSI division
- 03 Concrete: 03 10 forming, 03 20 reinforcing, 03 30 cast-in-place
What a concrete estimate measures
Concrete is drawn on the foundation plan, the framing plans, the sections and the schedules. Footing and column schedules give the sizes; the general notes give the mix strength, cover and reinforcing. A complete concrete takeoff measures:
- Concrete by element and by mix, in cubic yards: footings, grade beams, walls, columns, beams and slabs.
- Reinforcing steel bar by bar, converted to pounds, and welded wire fabric in square feet.
- Formwork in square feet of contact area: the faces of concrete that a form touches.
- Excavation and backfill for footings, in cubic yards.
- Vapor barrier and base course under slabs, in square feet.
- Finishing in square feet, and saw-cut or tooled joints in linear feet.
- Embeds, anchor bolts, dowels, waterstops and blockouts, each or in linear feet.
- Pumping, testing, curing, and hot- or cold-weather protection where the job needs them.
Concrete volume formulas for each element
Every concrete volume is length × width × thickness in feet, divided by 27 to turn cubic feet into cubic yards. Slab and wall thicknesses are usually given in inches, so divide them by 12 first.
| Element | Formula | Example | Cubic yards |
|---|---|---|---|
| Slab | Length × width × (thickness in. ÷ 12) ÷ 27 | 40 × 30 ft, 4 in. thick | 14.81 |
| Continuous footing | Length × width × depth ÷ 27 | 100 lin ft, 2 ft wide, 1 ft deep | 7.41 |
| Spread footing | Length × width × depth × number ÷ 27 | Ten 4 × 4 × 1.5 ft pads | 8.89 |
| Wall | Length × height × (thickness in. ÷ 12) ÷ 27 | 100 ft long, 8 ft high, 8 in. thick | 19.75 |
| Round column | 3.1416 × radius² × height × number ÷ 27 | Four 12 in. columns, 10 ft high | 1.16 |
| Rectangular column or beam | Width × depth × length ÷ 27 | 12 × 24 in. beam, 30 ft long | 2.22 |
Thickened edges, turndowns and slab depressions add up quickly and are the most common reason a slab estimate comes up short. Measure them as their own lines, from the slab sections.
How many square feet a cubic yard of concrete covers
A cubic yard is 27 cubic feet, so the slab area it covers is 324 divided by the thickness in inches. This table is the quickest check on a slab takeoff.
| Slab thickness | Sq ft per cubic yard | Cubic yards per 1,000 sq ft |
|---|---|---|
| 3-1/2 in. | 92.6 | 10.80 |
| 4 in. | 81.0 | 12.35 |
| 5 in. | 64.8 | 15.43 |
| 6 in. | 54.0 | 18.52 |
| 8 in. | 40.5 | 24.69 |
| 10 in. | 32.4 | 30.86 |
| 12 in. | 27.0 | 37.04 |
How much extra concrete to order
The National Ready Mixed Concrete Association recommends ordering 4 to 10 percent over plan dimensions for waste, over-excavation, form deflection and other contingencies. Small errors matter: a 4 inch slab poured just 1/8 inch thick is 3 percent short, or 1 cubic yard on a 32 yard order.
- Use the low end, around 4 to 5 percent, for repetitive work on a well-graded, compacted base.
- Use the high end, up to 10 percent, for footings dug in soil, irregular subgrade and small scattered pours.
- Elevated slabs on deflecting forms and slabs over granular fill need more than the plan volume suggests.
- On a ready-mix order, check the last two or three loads against what is left to pour, so the job does not wait for a short load.
Bags of concrete per cubic yard, for small pours
For a small pour, such as a pad, a post footing or a repair, premixed bags can be cheaper than a ready-mix truck. QUIKRETE publishes these yields for its concrete mix:
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 50 lb | 0.375 cu ft | 72 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
| 90 lb | 0.675 cu ft | 40 |
Rebar, formwork and the rest of the estimate
| Item | How it is measured | Unit |
|---|---|---|
| Reinforcing steel | Each bar's count, length, laps and hooks from the schedules and sections, × weight per foot: #4 = 0.668 lb, #5 = 1.043 lb, #6 = 1.502 lb. | Pounds or tons |
| Welded wire fabric | Slab area plus laps, by mesh style. | Square feet |
| Formwork | The faces the forms touch: slab edges, both sides of footings and walls, column faces, beam sides and soffits. | Sq ft of contact area |
| Excavation and backfill | Footing volume plus working room, less the concrete placed, for backfill. | Cubic yards |
| Vapor barrier | Slab area plus laps and turn-ups. | Square feet |
| Finishing | Slab area, by finish type: trowel, broom, exposed or polished. | Square feet |
| Joints | Saw-cut, construction and isolation joints, with sealant where specified. | Linear feet |
Rebar is where concrete estimates most often go wrong, because the amount per cubic yard varies widely from one element to the next. Measure it bar by bar from the drawings. Bar weights, lap lengths and a calculator are in the rebar sizes and weight chart.
Concrete volume calculator
Choose an element and enter its size to get the neat volume, an order quantity with waste, the form contact area and, for small pours, the number of 80 lb bags. It is meant for checking a takeoff or pricing one element; a building needs every element measured from the drawings.
Concrete volume calculator
- Concrete, neat
- 14.81 cu yd
- Concrete to order
- 15.56 cu yd (with 5% waste)
- Form contact area
- 47 sq ft
- Or 80 lb bags, for small pours
- 701
Volume is length × width × thickness in feet ÷ 27. Forms are the edge of a slab, both sides of a footing or wall, and the round face of a column; footing ends, bulkheads and blockouts are not included. An 80 lb bag of premixed concrete yields about 0.60 cu ft, so 45 bags make a cubic yard. Rebar, mesh, vapor barrier and finishing are measured separately.
A real concrete estimate, line by line
These are the totals by material from a concrete estimate we delivered for a one-story fire station in Florida of about 14,200 square feet, with footings, walls, columns, beams and slabs. Lines of the same material are combined across all elements, and the unit cost is labor plus material.
| Item | Quantity | Cost | Unit cost |
|---|---|---|---|
| Concrete in place, 3000 and 4000 PSI | 702 CY | $296,613 | $422.53 per CY |
| Reinforcing steel | 52,380 LB | $105,788 | $2.02 per LB |
| Footing excavation | 587 CY | $35,488 | $60.46 per CY |
| Formwork | 10,801 SF | $21,386 | $1.98 per SF |
| Backfill | 412 CY | $17,779 | $43.15 per CY |
| Vapor barrier under slabs | 15,283 SF | $17,148 | $1.12 per SF |
| Precast concrete window sills | 382 LF | $10,610 | $27.77 per LF |
| Welded wire fabric | 7,084 SF | $10,442 | $1.47 per SF |
| Saw-cut joints with sealant | 1,233 LF | $4,408 | $3.58 per LF |
Reinforcing averaged about 75 pounds per cubic yard on this building, but it varied widely between the footings, walls and slabs, which is why it was taken off bar by bar. On an 8,300 square foot multi-story building in California, with a mat foundation and elevated slabs, concrete trade cost was $846,899, or $102.52 per square foot. The line items are on the concrete estimating page, and the full pages are on the samples page.
Common concrete estimating mistakes
- Measuring a slab at its nominal thickness and missing thickened edges, turndowns and depressions.
- Pricing rebar as pounds per cubic yard from another building instead of from the schedules.
- Pricing formwork as a percentage of the concrete instead of by contact area.
- Ordering the neat volume with no allowance for waste, subgrade and form deflection.
- Leaving out the vapor barrier, base course, joints and sealant.
- Pricing every mix the same when footings, slabs and elevated work call for different strengths.
- Forgetting the pump, testing, and hot- or cold-weather protection.
Getting a concrete takeoff done for you
We prepare concrete and rebar takeoffs and estimates for concrete contractors, rebar fabricators and general contractors in every state, usually in 24 to 48 hours, priced to the project's ZIP code, with marked-up drawings and an editable Excel workbook. See concrete estimating services or send the drawings for a free quote.
Common questions
Multiply length × width × thickness, all in feet, to get cubic feet, then divide by 27. A 40 by 30 foot slab, 4 inches thick, is 40 × 30 × 0.333 = 400 cubic feet, or 14.81 cubic yards before waste.
81 square feet at 4 inches thick, 64.8 at 5 inches and 54 at 6 inches. The rule is 324 divided by the thickness in inches.
The National Ready Mixed Concrete Association recommends 4 to 10 percent over plan dimensions for waste, over-excavation, form deflection and other contingencies, more for footings in soil and small scattered pours.
About 45. An 80 lb bag of QUIKRETE Concrete Mix yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet. With 60 lb bags it is 60, and with 40 lb bags 90.
In square feet of contact area: the faces of concrete the forms touch. For a wall that is both sides, length × height × 2; for a slab on grade, the edge perimeter × thickness; for a beam, the sides and the soffit.
It depends on the element, the mix and the location. On a Florida fire station we estimated, concrete in place averaged about $422 per cubic yard, labor plus material, before rebar, formwork, earthwork and markups.
It varies too much by element to use a ratio for bidding. As one data point, the fire station in this guide averaged about 75 pounds per cubic yard overall. Take rebar off bar by bar from the schedules.
Division 03 Concrete. Forming is 03 10 00, reinforcing 03 20 00, cast-in-place concrete 03 30 00, finishing 03 35 00 and precast 03 40 00.