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newSchoolWorks.com › VoTechWorks › Building & Construction › Construction (general) › Materials Estimating for Construction › Lesson 4
BLD-CONS02-09 · Lesson 4 · 10 clock hours · lab

Concrete and Masonry Take-Off

Objective. Students will calculate concrete volume (slabs, footings, walls) and masonry unit quantities (CMU block and brick) from foundation and detail drawings, applying correct waste allowances and converting to supplier order units.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why Accurate Take-Offs Matter

Before a single yard of concrete is poured or a single block is set, someone has to calculate exactly how much material to order. Order too little and the pour stops mid-slab—a serious defect. Order too much and the excess concrete is wasted, often at significant cost. A concrete and masonry take-off is the process of reading construction drawings and converting dimensions into supplier order quantities. Done correctly, it protects both the schedule and the budget.

Reading the Drawings

Take-offs start at the drawings. A foundation plan is a top-down view showing the outline of the building, slab areas, footing locations, and pier locations. An elevation drawing shows a wall face from the side, revealing height, coursing, and openings. Before you calculate anything, confirm the drawing scale, locate the north arrow, and identify each element you will estimate: slabs, continuous footings, pier footings, CMU walls, and any brick veneer. Use a scale rule to verify spot dimensions against printed notes—drawings are sometimes plotted at a non-standard size.

Concrete Volume: The Core Formulas

Ready-mix concrete is ordered by the cubic yard (CY). One cubic yard equals 27 cubic feet. All dimensions must be in feet before you divide by 27.

Rectangular slab on grade:

> Volume (CY) = (Length × Width × Thickness) ÷ 27

A 4-inch slab thickness converts to 0.333 ft (4 ÷ 12).

Continuous (strip) footing:

> Volume (CY) = (Length × Width × Depth) ÷ 27

For a perimeter footing, measure the centerline length all the way around to avoid double-counting corners.

Pier (isolated) footing:

> Volume (CY) = (Length × Width × Depth) ÷ 27, then multiply by the number of piers.

Calculate each element separately, then sum them. This makes checking and corrections easy.

Concrete Waste Allowance

Readymix trucks cannot deliver a fraction of a yard cleanly, and some concrete is always lost to over-excavation, form irregularities, and spillage. Standard practice is to add 5–8% to the calculated volume before placing the order. For residential and light commercial work, 5% is common on straightforward pours; 8% is used when forms are complex or subgrade conditions are uncertain. Always round up to the nearest quarter yard when writing the order—never round down.

Writing a Ready-Mix Order

A concrete order specifies more than just cubic yards. The supplier needs:

Recording these details on a formal order form creates a paper trail if a dispute arises about what was delivered.

Masonry Unit Take-Off: CMU Block

Concrete masonry units (CMU) are ordered by the piece. Standard 8-inch CMU (nominally 8 in × 8 in × 16 in, including the mortar joint) covers approximately 1.125 blocks per square foot of wall face when laid in standard running bond with 3/8-inch mortar joints. In practice, estimators commonly round to 1.125 blocks/SF or use the simplified figure of 1.0 block per SF and then apply a waste factor—know which approach your employer or instructor uses and be consistent.

Steps for a CMU take-off:

1. Calculate gross wall face area (height × length) for each wall section.

2. Subtract openings (doors, windows) to get net wall area.

3. Multiply net area by 1.125 blocks/SF to get the base block count.

4. Add 5% for breakage (multiply by 1.05), then round up to the nearest whole block.

Masonry Unit Take-Off: Brick Veneer

Standard modular brick (nominally 2-5/8 in × 3-5/8 in × 7-5/8 in with a 3/8-inch mortar joint) covers approximately 6.75 bricks per square foot of wall face in running bond. Apply the same logic: calculate net face area, multiply by 6.75, add 5% waste, round up.

Safety Notes for the Lab

This is an office/classroom lab, but the habits you build here carry to the field. When you later work with ready-mix concrete:

For the lab itself, handle sharp-edged drawings and scale rules carefully and keep work surfaces clear.

Order of Operations — Best Practice

1. Mark up each element on the drawing with a colored pencil as you measure it—do not measure the same element twice.

2. Record every dimension in a take-off worksheet before entering any formula.

3. Compute element by element, then sum.

4. Apply waste last, after summing all elements.

5. Double-check unit conversions (inches to feet, feet to yards).

A take-off that is neat and organized can be reviewed and corrected; a take-off scribbled on a napkin cannot.

Key terms9

Take-offThe process of reading construction drawings and quantifying materials needed for a project, used as the basis for ordering and pricing.
Cubic yard (CY)The standard unit for ordering ready-mix concrete; equal to 27 cubic feet. All concrete volume calculations must be converted to this unit before ordering.
SlumpA field measurement of fresh concrete workability, expressed in inches; a higher slump indicates a wetter, more fluid mix.
Mix designThe specified combination of cement, aggregate, water, and admixtures for a concrete pour, usually defined by minimum compressive strength at 28 days (psi).
Concrete masonry unit (CMU)A standard hollow or solid concrete block used in wall construction; the nominal 8×8×16-inch unit is the most common and is ordered by piece count.
Waste allowanceA percentage added to the calculated material quantity to account for breakage, spillage, cutting loss, and minor field variation; typically 5–8% for concrete and 5% for CMU or brick.
Net wall areaThe gross face area of a wall section minus the area of all openings (doors, windows); the correct base for a masonry unit take-off.
Continuous (strip) footingA linear concrete footing that runs along the perimeter or beneath a load-bearing wall; volume is calculated using centerline length to avoid double-counting corners.
Running bondA masonry pattern in which each unit is offset by half a unit horizontally from the course above and below; the most common pattern for CMU and brick veneer.

Worked examples4

1. A 4-inch slab on grade is 24 ft long and 20 ft wide. What volume of concrete must be ordered, including a 5% waste allowance? Round up to the nearest 0.25 CY.
  1. Convert thickness: 4 in ÷ 12 = 0.333 ft
  2. Calculate raw volume: 24 ft × 20 ft × 0.333 ft = 160.0 cu ft
  3. Convert to cubic yards: 160.0 ÷ 27 = 5.926 CY
  4. Apply 5% waste: 5.926 × 1.05 = 6.222 CY
  5. Round up to nearest 0.25 CY: 6.25 CY
Answer: Order 6.25 CY of concrete.
2. A perimeter strip footing is 12 in wide, 8 in deep, and runs along all four sides of a 24 ft × 20 ft building. Using centerline dimensions, what is the footing volume before waste?
  1. Convert footing dimensions: width = 12 in ÷ 12 = 1.0 ft; depth = 8 in ÷ 12 = 0.667 ft
  2. Calculate centerline perimeter: 2 × (24 + 20) = 88 ft (for a simple rectangular footing, centerline length equals the perimeter of the building outline when footing width is small relative to building size; use 88 ft here as given)
  3. Calculate volume: 88 ft × 1.0 ft × 0.667 ft = 58.7 cu ft
  4. Convert to cubic yards: 58.7 ÷ 27 = 2.174 CY
  5. No waste applied yet (will be added when summing all elements)
Answer: Footing volume before waste = 2.17 CY.
3. Two square pier footings, each 2 ft × 2 ft × 1 ft deep, are included in the foundation. What is their combined concrete volume in cubic yards?
  1. Volume of one pier: 2 ft × 2 ft × 1 ft = 4 cu ft
  2. Two piers: 4 × 2 = 8 cu ft
  3. Convert to cubic yards: 8 ÷ 27 = 0.296 CY
Answer: Combined pier volume = 0.30 CY (rounded to two decimal places).
4. A CMU block wall is 32 ft long and 8 ft tall with one door opening 3 ft wide × 7 ft tall. Using 1.125 blocks per SF and 5% breakage, how many blocks must be ordered?
  1. Gross wall area: 32 ft × 8 ft = 256 SF
  2. Door opening area: 3 ft × 7 ft = 21 SF
  3. Net wall area: 256 – 21 = 235 SF
  4. Base block count: 235 × 1.125 = 264.4 blocks
  5. Apply 5% breakage: 264.4 × 1.05 = 277.6 blocks
  6. Round up to nearest whole block: 278 blocks
Answer: Order 278 CMU blocks.

The math in this lesson3

Learners compute slab, perimeter-footing and pier volumes in cubic yards and CMU block counts with 5% breakage.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstration at the board: derive volume formulas for rectangular slabs, continuous footings, and pier footings; compute an example order including 5–8% over-order for concrete and 5% waste for CMU; discuss why ready-mix is ordered by the cubic yard and block is ordered by the piece. · Lab exercise — concrete: students receive a foundation plan with a 4-inch slab on grade, perimeter footings, and two interior piers; they calculate volume for each element separately, sum to total cubic yards, and add waste; they then write a mock ready-mix order specifying cubic yards, slump, and mix design (instructor provides a blank order form). · Lab exercise — masonry: students receive an elevation drawing of a CMU block wall (8-inch block, standard coursing); they calculate the number of blocks needed per square foot of wall face, multiply by the wall area, apply a 5% breakage factor, and produce a block order by count; a second tier adds a running-bond brick veneer calculation on the same wall.
Materials: Foundation plan and elevation drawings (instructor-prepared), concrete take-off worksheet, CMU/brick take-off worksheet, blank ready-mix order form, calculator, scale rule, ACI 332 reference guide (basic residential concrete construction, for context)
Check: Both completed take-off worksheets scored against answer key; concrete volume must be within 0.5 CY of key and block count within 5%; students who miss either threshold redo the calculation with instructor coaching before the next lesson.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Construction Technology – Materials Estimating
1. Ready-mix concrete is sold and ordered in which unit?
NCCER Construction Technology – Materials Estimating
2. A slab on grade measures 30 ft × 16 ft × 4 inches thick. What is the raw concrete volume in cubic yards (before waste)?
NCCER Construction Technology – Materials Estimating
3. When calculating the concrete volume for a perimeter strip footing, why should you use the centerline length rather than the outside perimeter?
NCCER Core – Construction Math
4. A standard waste allowance when ordering concrete for a straightforward residential slab is:
NCCER Construction Technology – Materials Estimating
5. A masonry take-off shows a wall with a gross face area of 400 SF and two window openings totaling 40 SF. Using 1.125 CMU blocks per SF and a 5% breakage allowance, how many blocks should be ordered?
NCCER Construction Technology – Materials Estimating
6. Which information is NOT typically required on a ready-mix concrete order form?
OSHA 10 – Construction Hazard Recognition
7. Fresh concrete poses which primary skin hazard that workers must protect against with gloves and boots?
NCCER Construction Technology – Materials Estimating
8. Approximately how many standard modular bricks are needed per square foot of wall face in a running-bond veneer (including mortar joints)?
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