Concrete Takeoff Guide: Cubic Yards, Rebar, Formwork, and Slab Math

A concrete takeoff is the full count of every cubic yard, pound of rebar, and square foot of formwork on a job. This guide walks you through the whole process in plain English, from reading the plans to shipping a tight bid. Whether you are new to estimating or you have been at it for twenty years, you will pick up something useful.

1. What a Concrete Takeoff Is

A concrete takeoff is a measured list of all the concrete work on a project. It answers three questions: how much concrete do we need, how much steel goes inside it, and how much forming material holds it in place. Think of it like a grocery list for a huge cake: you need the batter (concrete), the frame that holds the shape (formwork), and the reinforcement that keeps it from falling apart (rebar or wire mesh).

The output of the takeoff becomes the foundation of your bid. Get the quantities wrong and the bid is wrong, even if your unit prices are perfect. That is why estimators spend more time on takeoff than on pricing.

The three quantities you always need

• Volume in cubic yards (CY). This is what the ready-mix truck delivers.
• Reinforcement in pounds (lbs) or tons. This is rebar, welded wire mesh, and sometimes post-tension cable.
• Formwork in square feet of contact area (SFCA). This is the wood, steel, or aluminum that holds the concrete until it cures.

2. Reading the Plans

Concrete work is called out on the structural drawings, usually labeled S-1, S-2, S-3, and so on. The architectural drawings (A-series) show you where the walls and floors go, but the structural drawings tell you exactly how thick, how tall, and what steel is inside.

Sheets you will open every time

• S-1 General Notes. Concrete strength (typically 3000 psi for slab on grade, 4000-5000 psi for structural), rebar grade (Grade 60), cover requirements, and lap lengths.
• S-2 Foundation Plan. Shows footings, piers, grade beams, and slab edges in plan view.
• S-3 Footing / Column / Wall Schedules. Tables that tell you the size and reinforcement of each marked element.
• S-4 and up, Framing Plans. Elevated slabs, beams, and decks.
• Details. Typical footing details, wall sections, slab edge details, and embed locations.

Start with the schedules, then the plan

Always read the schedules first. They are like a key to a map. A footing schedule might say F1: 4'-0" x 4'-0" x 12" thick with (5) #5 bars each way. Now when you see the tag F1 anywhere on the foundation plan, you know exactly what it is.

3. Cubic Yard Math

Concrete is sold by the cubic yard. One cubic yard equals 27 cubic feet. Almost every volume calculation you do will end with dividing cubic feet by 27.

The universal formula

Volume (CY) = Length (ft) x Width (ft) x Thickness (ft) / 27

Remember to convert inches to feet. A 6-inch slab is 0.5 ft thick. A 4-inch slab is 0.333 ft. An 8-inch wall is 0.667 ft. Punch this in wrong and your quantity is off by a factor of 10 or more.

Slab on grade

For a simple rectangular slab, multiply the two plan dimensions by the thickness and divide by 27. Example: a warehouse floor 120 ft by 80 ft at 6 inches thick. 120 x 80 x 0.5 / 27 = 177.8 CY.

If the slab has thickened edges or interior thickenings, calculate those separately and add them. Do not forget slab depressions for floor drains or equipment pads.

Footings

Spread footings are boxes. Length x width x thickness, divide by 27, multiply by the count. Continuous footings (also called strip footings or wall footings) are long prisms. Total linear feet x width x thickness / 27.

Walls

Wall volume is length x height x thickness / 27. Subtract openings larger than 8 square feet (doors, big windows, equipment openings). Openings smaller than that are usually left in the gross quantity because you need the concrete anyway for the buck-out forms.

Columns, piers, and pilasters

Count each one on the plan. Multiply the plan dimensions by the height (top of footing to bottom of slab or top of wall). For round columns, use Pi x radius squared x height / 27.

4. Rebar Takeoff

Rebar (short for reinforcing bar) is the steel inside the concrete that takes tension loads. Concrete is strong in compression but weak in tension. Rebar fixes that.

Bar sizes and weights

Rebar is sized in eighths of an inch. A #4 bar is 4/8 or 1/2 inch in diameter. A #8 bar is 1 inch. Here are the weights you will use all day:

• #3 = 0.376 lb/ft
• #4 = 0.668 lb/ft
• #5 = 1.043 lb/ft
• #6 = 1.502 lb/ft
• #7 = 2.044 lb/ft
• #8 = 2.670 lb/ft

The three-step method

1. Read the schedule to find bar size and spacing (for example, #5 at 12 in. on center each way).
2. Calculate linear feet. For a 20 ft by 30 ft slab at #5 at 12" O.C. each way: 20 bars running 30 ft long plus 30 bars running 20 ft long = 600 + 600 = 1,200 linear feet.
3. Convert to weight. 1,200 ft x 1.043 lb/ft = 1,252 lbs. Add 5-8% for laps and waste = about 1,330 lbs.

Do not forget

• Lap splices. Bars come in 20 or 60 ft lengths. Long runs need splices, usually 40 bar diameters.
• Bends and hooks. Corners, ties, and hooks add length. Use a bar bending schedule if provided.
• Chairs and bolsters. These hold rebar at the right height. Count them as a lump sum or per 100 sq ft.
• Accessories. Tie wire, dowel baskets, and sleeves all add to the material bill.

5. Formwork (SFCA) Takeoff

Formwork is the temporary mold that holds wet concrete. It is measured in SFCA, which stands for Square Feet of Contact Area. SFCA is the surface of the concrete that actually touches the form.

Wall formwork

A wall 100 ft long and 10 ft tall, poured full height, has 1,000 sq ft on one face. But forms go on both sides, so SFCA = 2,000 sq ft.

Footing formwork

Footings usually only need forms on the sides, not the top or bottom. A continuous footing 100 ft long and 12 inches deep has 100 ft x 1 ft x 2 sides = 200 SFCA.

Slab edge

A 4-inch slab has a 4-inch edge. For a 100 ft long slab edge, SFCA = 100 x 0.333 = 33 sq ft. Small, but you still need to count it because someone has to build it.

Plywood and lumber

Standard form plywood is 4 ft x 8 ft (32 sq ft per sheet). You will generally reuse plywood 5-10 times on a job. Do not bid the full SFCA as new plywood. Crews price it as a rental or amortized cost.

6. Waste Factors and Add-Ons

A waste factor is a percentage you add to the neat (exact) quantity to cover spillage, overpour, trimming, and errors. Skip this and you will run short on pour day, which is a very expensive problem.

Standard concrete waste factors

• Slab on grade: 5-10% (lower if subgrade is flat and compacted, higher if rough)
• Footings: 8-12% (the bottom of the trench is never perfectly level)
• Walls: 3-5% (tight forms control waste well)
• Elevated slabs: 3-5% (decks are usually controlled)
• Small pours, pads, curbs: 10-15% (lots of little losses add up)

Do not forget pump loss

If you are using a concrete pump, the pump line holds roughly 1 cubic yard. That concrete is wasted at the end of the pour. Add it to your order.

Rebar waste

Use 5% for simple straight runs and 8-10% for heavily reinforced items like mat foundations or beams.

7. AI Concrete Takeoff

Traditional takeoff means opening a PDF viewer with a digital measuring tool like Bluebeam or On-Screen Takeoff, then clicking along every edge of every footing, slab, wall, and column. A 20,000 sq ft building can take an experienced estimator 8 to 16 hours.

AI concrete takeoff flips that. You upload the plan set. The software reads the drawings, identifies structural elements using computer vision and language models, and produces a full quantity list in minutes.

What PILRS does for a concrete takeoff

• Reads the foundation plan, structural schedules, and details automatically.
• Identifies footings, piers, slabs, walls, columns, and grade beams.
• Calculates volume in CY, rebar in pounds, and formwork in SFCA.
• Applies waste factors you set in a template.
• Exports to CSV, Excel, or directly into a bid form.

Why estimators still review the output

AI gets you 90-95% of the way there. A senior estimator still needs to check for non-standard details, owner-specific notes, and judgment calls on waste. The big win is time. What was 12 hours becomes 1 hour of review.

8. Bid Day Checklist

Before you send the bid out, run through this list. It will catch more mistakes than anything else.

1. Did you include every footing type on the schedule? Cross-check count.
2. Did you pick up slab thickenings at column lines and bearing walls?
3. Did you add rebar for all dowels between footings and walls or slabs and walls?
4. Did you include slab-on-grade vapor barrier and subbase if in your scope?
5. Did you add pump yardage, cold-weather protection, or hot-weather admixtures if required?
6. Did you include curing compound, sealer, and saw cutting for control joints?
7. Did you include an allowance for embeds, anchor bolts, and column base plates set by your crew?
8. Did you check the spec section 03 30 00 for any finish, flatness (FF/FL), or tolerance requirements that affect labor?