Reading a set of concrete plans accurately is one of the most valuable skills a flatwork or foundation contractor can have. Miss a detail in the drawings and you're either under-bidding the job or pouring the wrong thing. This guide walks through the key elements of a concrete plan — scale, symbols, slab vs. footing identification, rebar callouts, and a practical takeoff workflow.
Start with the Title Block and General Notes
Before you look at any dimensions or details, find the title block — usually in the lower right corner of each sheet. It tells you:
- Project name and address — confirms you have the right set
- Sheet number and revision — always work from the latest revision; old sets get people in trouble
- Drawing scale — this is critical before you take a single measurement
- Engineer of record — who to call when something doesn't make sense
General notes, usually on the first structural sheet (S0.0 or S1.0), specify the concrete mix design, cover requirements for rebar, and any special curing or admixture requirements. Read these before touching the plan sheets — they govern everything.
Understanding Scale Notation
Architectural and structural drawings are reduced representations of the real thing. The scale tells you the ratio of drawing measurement to actual size.
| Notation | Meaning | Common use |
|---|---|---|
| 1/4" = 1'-0" | 1 inch on paper = 4 feet real | Residential floor plans |
| 1/8" = 1'-0" | 1 inch on paper = 8 feet real | Site plans, small commercial |
| 1" = 10' | Engineering scale, 1 in = 10 ft | Civil / site work |
| 3/4" = 1'-0" | 1 inch on paper = 16 inches real | Details and sections |
| NTS | Not to scale | Schematic or detail only — never measure |
Identifying Plan Symbols
Structural concrete drawings use a consistent set of symbols. Getting familiar with these saves time and prevents misreads.
Reading Rebar Callouts
Reinforcing steel is specified in a standard format. Once you know the pattern, you can decode any rebar callout quickly.
Bar Size
Rebar sizes in the U.S. are designated by number, representing eighths of an inch in diameter:
- #3 bar — 3/8" diameter, lightest common residential bar
- #4 bar — 1/2" diameter, standard residential and light commercial
- #5 bar — 5/8" diameter, heavier footings and walls
- #6+ — structural work, retaining walls, heavy foundations
Spacing Callout
Rebar is specified with bar size and spacing in both directions. Example:
#4 @ 18" EW (EACH WAY)
This means #4 bars at 18 inches on center, running in both directions. "EW" or "E.W." means the same bar pattern applies horizontally and vertically.
Sometimes you'll see different spacing per direction:
#4 @ 12" N-S, #4 @ 18" E-W
Cover Requirement
Cover is the distance from the outer face of the concrete to the nearest rebar. It's critical for corrosion protection. The general notes will specify required cover — common values:
- Slabs on grade: 3/4" to 1-1/2" (check local code)
- Footings cast against earth: 3"
- Exposed to weather: 1-1/2" to 2"
Slab Areas vs. Footings: How to Tell Them Apart
On a plan view (looking straight down), slabs and footings can look similar — both are bounded areas. Here's how to distinguish them:
- Solid boundary = slab edge. The slab is what you see — it's at finished grade.
- Dashed lines = hidden below grade. Footings are below the slab and shown dashed on the foundation plan.
- Hatching or fill pattern inside a shape typically indicates a concrete element in cross-section.
- Section tags (triangle or circle with a letter/number) point to a detail sheet showing the actual shape in cross-section. Always find and read the referenced section — the plan view doesn't show you depth.
Dimension Takeoff Workflow
A systematic approach prevents missed areas and double-counting. Here's a repeatable process for pulling quantities from a concrete plan:
Orient yourself first
Find north. Identify the building perimeter and main reference grid lines (usually labeled A, B, C... and 1, 2, 3...). Everything gets measured relative to the grid.
Identify all concrete elements
Make a list: slabs on grade, elevated slabs, strip footings, pad footings, grade beams, columns, walls. Don't assume you've found everything — check every sheet including sections and details.
Gather dimensions for each element
Use only dimensioned values — never scale from the drawing. For irregular shapes, break them into rectangles or triangles and sum the areas. Note the thickness from sections or notes for each element.
Calculate volume and reconcile
Convert each element to cubic yards: (length × width × thickness in feet) ÷ 27. Sum all elements. Cross-check your total against any volume schedule the engineer may have provided — discrepancies over 5% warrant a re-check.
Apply waste factor and order
Add your standard waste factor (typically 5–8% for slabs, up to 10% for footings due to irregular subgrade). Round up to the nearest quarter yard when calling the plant.
Common Mistakes to Avoid
- Working from an outdated revision. Always verify you have the current drawings before starting takeoff.
- Scaling off a PDF without confirming print scale. Use dimensioned numbers only.
- Missing thickened edges. Perimeter turndowns and thickened areas at load points add significant volume that the plan view doesn't make obvious.
- Ignoring the general notes. Mix design, cover, admixtures, and special requirements are all in the notes — not on the plan sheets.
- Treating a control joint as a pour break. Control joints are saw-cut joints to control cracking. Construction joints (actual pour breaks) are a separate detail and have different forming requirements.