Learning how to calculate concrete yardage is the first skill every estimator picks up, and it is also where many concrete bids quietly go wrong. The volume formulas are easy. What costs money is everything around them: double-counted intersections, rebar that was priced by the pound but never measured, formwork treated as an afterthought, and a waste factor that nobody can explain. This guide takes you through a complete concrete takeoff in the order a working estimator does it, with formulas, conversion factors and a full worked example.
If you would rather have the quantities prepared from your drawings, our concrete estimating services deliver volumes, reinforcing and formwork by element, ready to price. If you want to understand the method first, keep reading.
What a concrete takeoff really includes
A concrete takeoff is not one number. It is at least five quantities that move together: concrete volume in cubic yards, reinforcing steel by size and weight, formwork in square feet of contact area, accessories and embedded items by count or length, and finishing by area and class. Each is priced differently and each is installed by different labor. A takeoff that reports only cubic yards is a material list, not an estimate.
For a broader view of how concrete fits with masonry and the rest of the structure, see our overview of concrete and masonry estimating for USA contractors. This post goes deeper on the math.
Step 1: Gather the right documents
Concrete information is spread across the set. Pull these before you measure anything:
- Structural general notes, which give concrete strengths, cover, lap lengths, bar grades and curing or testing requirements.
- Foundation plan, framing plans and sections, which give element sizes and elevations.
- Footing, column, beam and wall schedules, which give sizes and reinforcing by mark.
- Architectural and civil drawings, for slab edges, pads, curbs, sidewalks, equipment bases and site concrete.
- Specifications, usually in Division 03, for mix designs, finish classes, joints, admixtures and tolerances.
Compare the structural sheets with the architectural ones. Slab depressions for tile, housekeeping pads under equipment and sloped slabs at drains often appear on only one discipline. Our guide to reading construction plans for estimating shows how to cross-check sheets so these items are not missed.
Step 2: Calculate concrete volume by element
Work in cubic feet, then divide by 27 to get cubic yards. Keep each element type on its own line, since forming, reinforcing and placement methods differ. Convert all dimensions to feet before multiplying: 6 inches is 0.5 feet, 8 inches is 0.667 feet.
Slabs on grade
Volume = length x width x thickness. A 6,000 square foot slab at 6 inches thick holds 6,000 x 0.5 = 3,000 cubic feet, or 111.1 cubic yards. Remember thickened edges, turn-down footings and trench or equipment pits, which add volume beneath the nominal thickness. Where the slab is sloped, use the average thickness.
Footings
Continuous footings: width x depth x total length. A footing 24 inches wide and 12 inches deep is 2 square feet in cross-section, so every linear foot is 2 cubic feet. Spread footings: length x width x depth x count, taken from the footing schedule by mark. Do not forget stepped footings, where the depth changes.
Walls and piers
Walls: length x height x thickness. Take the height from the top of footing to the top of wall, not floor to floor. Piers and square columns: width x depth x height x count. Round columns and piers: pi x radius squared x height. Subtract large openings, but leave small block-outs undeducted if your convention is to ignore them.
Beams, elevated slabs and slabs on metal deck
Beams are measured below the slab, so take depth minus slab thickness to avoid double counting. Slabs on metal deck need the volume above the deck plus the volume in the flutes. Deck manufacturers publish concrete volume per square foot for each profile and gauge, and using the published figure is more accurate than guessing an average.
Intersections and deductions
Where footings meet columns, or walls meet footings, volume is easy to count twice. Pick a rule, such as columns measured from the top of the footing, and apply it everywhere. Deduct recesses, sleeves and block-outs only when they are large enough to matter.
Step 3: Add waste and convert to orderable yards
The measured volume is the net volume. The concrete you order is larger because of over-excavation, uneven subgrade, form deflection, spillage and pump or chute losses. Many estimators start with an allowance of about 5 to 10 percent and adjust by element: sloppy trench footings poured against earth lose more than a flat slab placed on a smooth base. Your own records of ordered versus placed volume are the best source for this number.
Round to the way concrete is actually delivered. Ready-mix trucks commonly carry loads of around 10 cubic yards, and suppliers may charge short-load fees on small deliveries, along with fees for extra time on site. Pricing by the cubic yard without these add-ons understates small pours.
Step 4: Calculate rebar and reinforcing
Reinforcing is measured in linear feet by bar size, then converted to weight. Standard weights per linear foot are:
- #3: 0.376 lb
- #4: 0.668 lb
- #5: 1.043 lb
- #6: 1.502 lb
- #7: 2.044 lb
- #8: 2.670 lb
For a slab with bars at a given spacing each way, a quick method is: bars per foot of width = 12 divided by the spacing in inches, then multiply by the length for each direction. At 12 inches on center each way, every square foot of slab carries 2 linear feet of bar. A 5,000 square foot slab with #4 at 12 inches each way needs 10,000 linear feet, which weighs 10,000 x 0.668 = 6,680 pounds before laps and waste.
Add for laps, hooks, bends and cutting waste. Lap lengths come from the structural notes and are usually written as a number of bar diameters, so a longer bar needs a longer lap. Many estimators add a flat percentage for laps and waste on slabs and walls, and measure footings, beams and columns bar by bar from the schedules. Also count supports: chairs, bolsters and spacers, tie wire, and dowels where slabs tie into walls or footings. Welded wire reinforcement is measured in square feet with side and end laps, not by weight.
Step 5: Calculate formwork
Formwork is measured as square feet of contact area, abbreviated SFCA: the surface of concrete that touches the form. This is often the largest labor item in a concrete package, so it must be measured on its own.
- Walls: length x height x 2 faces, plus end forms and bulkheads at pour breaks.
- Footings: side forms equal perimeter x depth, unless the footing is poured against earth.
- Columns: perimeter x height.
- Elevated slabs: the soffit area plus edge forms.
- Beams: bottom and two sides.
- Slab on grade edges: linear feet of edge form by height.
Then decide on reuse. A wall form that is used eight times costs far less per use than a one-time form for a unique element, so the number of repetitions affects the price. Forming systems for tall walls, curved work or architectural finishes need their own rates. Add stripping, cleaning, bracing, shoring and reshoring, which are easy to leave off.
Step 6: Count accessories, joints and finishing
- Vapor barrier and base course under slabs, in square feet.
- Anchor bolts, embeds, sleeves, inserts and dowels, counted by mark.
- Control joints, isolation joints and sawcuts, in linear feet, with sealants where specified.
- Waterstops and expansion joint material in linear feet.
- Curing compound or curing methods, in square feet.
- Finishing by area and class: broom, float, steel trowel, or polished, with hardeners, sealers and tolerances where the spec calls for them.
- Grout under base plates and equipment.
Step 7: Equipment, placement and testing
Placement method changes cost. A slab placed directly from the truck chute costs less than concrete pumped to a third-floor deck or lifted by crane and bucket. Price pumps, line setup, crane time, finishing crews, power trowels, saws and screeds. Add cold-weather or hot-weather measures where the schedule requires them, and include concrete testing and special inspection if they are in your scope. The American Concrete Institute at concrete.org publishes the standards that most specifications reference, so check which ones the project cites.
Labor is where the margin is won or lost. For production rates, burdens and crew builds, read our guide to construction labor cost estimating.
A full worked example
These numbers are illustrative. A small warehouse has a 60 x 100 foot slab on grade, 6 inches thick, with a continuous perimeter footing 24 inches wide and 12 inches deep, and an 8-inch foundation wall 4 feet high on top. The perimeter is 2 x (60 + 100) = 320 linear feet.
- Slab: 6,000 sq ft x 0.5 ft = 3,000 cu ft, or 111.1 cu yd.
- Footing: 2 sq ft x 320 ft = 640 cu ft, or 23.7 cu yd.
- Wall: 320 ft x 4 ft x 0.667 ft = 853.3 cu ft, or 31.6 cu yd.
- Net total: 166.4 cu yd.
- With 7 percent waste: 166.4 x 1.07 = 178.1 cu yd, which is about 18 truckloads of 10 yards.
Formwork, assuming footing side forms and both wall faces:
- Footing sides: 2 x 320 ft x 1 ft = 640 SFCA.
- Wall faces: 2 x 320 ft x 4 ft = 2,560 SFCA.
- Total: 3,200 SFCA, before end forms, bulkheads and openings.
Reinforcing, assuming #4 at 12 inches each way in the slab and three continuous #5 bars in the footing:
- Slab: 6,000 x 2 = 12,000 ft x 0.668 = 8,016 lb.
- Footing: 3 x 320 = 960 ft x 1.043 = 1,001 lb.
- Subtotal: 9,017 lb. With 10 percent for laps and waste: 9,919 lb, or about 4.96 tons.
Wall reinforcing, dowels, anchor bolts, vapor barrier, joints, finishing and labor are then added as their own lines. This is how a concrete package turns from a volume into a price.
Items that are commonly missed
- Thickened slab edges, pits, sumps and trenches that add volume.
- Housekeeping pads, equipment bases and curbs shown only on mechanical or architectural sheets.
- Stair and ramp concrete, and the forming they need.
- Dowels, starter bars and anchor bolts.
- Sawcutting, joint fill and slab curing.
- Shoring, reshoring and stripping of elevated work.
- Pump, crane, testing and cold-weather costs.
Common concrete takeoff mistakes
- Reporting cubic yards only and skipping formwork and reinforcing as separate quantities.
- Counting volume twice at footing, column and wall intersections.
- Using a flat waste factor on every element regardless of how it is placed.
- Mixing inches and feet in a formula.
- Pricing rebar by weight with no allowance for laps, hooks and supports.
- Ignoring the reuse count on forms, which swings formwork cost widely.
- Leaving out short-load fees, pump charges and weekend premiums.
More errors like these, and how they affect bid accuracy, are covered in our list of common construction estimating mistakes, and the basics of organizing quantities are in our material takeoff guide. For excavation and site work that comes before the pour, see sitework estimating and takeoff.
Frequently asked questions
How many cubic yards of concrete do I need for a 20 x 20 slab that is 4 inches thick?
The area is 400 sq ft. At 4 inches (0.333 ft) thick, that is 133.3 cu ft, or 4.94 cu yd. With 10 percent waste, order about 5.4 cubic yards.
How do I convert cubic feet to cubic yards?
Divide by 27, because a cubic yard is 3 ft x 3 ft x 3 ft.
How much does a cubic yard of concrete weigh?
Normal-weight concrete weighs roughly 150 pounds per cubic foot, so about 4,000 pounds per cubic yard. This matters for trucks, pumps and temporary support of elevated pours.
What waste factor should I use for concrete?
Many estimators use about 5 to 10 percent, with higher allowances for trenches poured against earth and lower ones for flat slabs on a smooth base. Compare ordered and placed quantities on past jobs to set your own.
Is rebar included in the concrete price?
Not unless the estimate says so. Reinforcing, formwork, finishing and accessories are usually separate lines. Always state in the bid what is included.
Should formwork be measured by contact area or by volume?
Contact area. Forming labor follows the surface that touches the concrete, not the volume, so measure square feet of contact area for every element.
Get a concrete takeoff prepared from your drawings
We extract concrete volumes, reinforcing, formwork, joints, accessories and finishing by element, so you can apply current supplier pricing and your own crew rates. See our concrete estimation service, our general quantity and material takeoffs, or the full list of estimating services by trade. For the units and conversions used throughout this post, read our guide to takeoff units of measure and conversions.