Get a full bill of materials for any concrete element — concrete, rebar, formwork and base gravel — with ready-mix or bag counts, reinforcement weights, and cost estimate in one pass.
- Slab & Footing
- Wall & Column
- Beam & Pad
- Ready-Mix or Bags
- Rebar Weight
- Full Cost Estimate
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Bill of materials
What a Construction Material Estimator Does
A concrete volume calculator tells you how much concrete to order. A material estimator goes further: it produces the full bill of materials for an element — concrete, reinforcement, formwork and base gravel — with quantities and cost, so you can send one order to one supplier and start the work.
Concrete
Volume in cubic yards, plus a truck or bag count depending on the supply method. Ready-mix is ordered in cubic yards with a 10–11 yard minimum per truck.
Reinforcement
Rebar weight in pounds, based on a reinforcement ratio for the element type and level. Typical residential work uses 60–100 lb/yd³.
Formwork
Contact area for formwork in square feet, converted to 4×8 plywood sheets and form oil quantity. Only applies to elements with exposed sides.
Base gravel
Volume and weight of compacted base gravel under the element. Typical depth is 4 inches under slabs and footings, more for soft subgrade.
A slab on grade needs far less steel than a structural column. Using a single blanket rebar ratio across all elements is the most common estimating error — it under-orders rebar on columns and beams, and over-orders it on slabs. This estimator applies a specific ratio to each element type and lets you raise or lower it with the reinforcement level selector.
Concrete Ordering: Ready-Mix vs Bags
The two supply methods have very different cost profiles and different minimums. Choosing wrong is the most expensive single mistake in material estimating.
| Factor | Ready-mix (cubic yards) | Pre-mixed bags (80 lb) |
|---|---|---|
| Order unit | Cubic yard (1 yd³ = 27 ft³) | Bag (0.6 ft³ yield per 80 lb bag) |
| Price range | $140–$200 per yd³ delivered | $6–$9 per 80 lb bag |
| Volume per load | 10–11 yd³ per truck | ~45 bags per yd³ |
| Minimum order | 1–2 yd³ (small load fee) | 1 bag |
| Best for | Jobs over 2 yd³ | Jobs under 2 yd³ or difficult access |
| Placement speed | Fast — 30–60 min per truck | Slow — manual mixing |
| Consistency | Factory batched, verified | Depends on water added on site |
Break-even is around 2 cubic yards. Below 2 yd³, bags are usually cheaper and more practical. Above 2 yd³, ready-mix wins on cost, consistency and speed. Ready-mix also carries a short-load fee below 3 yd³ in most markets.
Reinforcement Ratios by Element Type
Reinforcement ratios are the fastest way to estimate rebar weight before a full structural design is available. These ratios are the standard industry values used on residential and light commercial work in pounds of steel per cubic yard of concrete.
| Element | Light (lb/yd³) | Standard (lb/yd³) | Heavy (lb/yd³) | Notes |
|---|---|---|---|---|
| Slab on grade | 30 | 60 | 100 | Mesh at light; #4 @ 12" both ways at standard |
| Strip footing | 60 | 100 | 150 | 2–4 longitudinal bars plus ties |
| Pad footing | 70 | 110 | 160 | Two-way mat at bottom |
| Retaining wall | 80 | 130 | 190 | Vertical and horizontal mats, both faces |
| Column | 120 | 180 | 260 | 4–8 vertical bars plus ties at spacing |
| Beam | 100 | 150 | 220 | Top and bottom bars plus stirrups |
When in doubt, order the standard ratio. Heavy ratios are for seismic zones, tall retaining walls and high-load columns. Light ratios are for temperature and crack control in lightly loaded slabs. Every ratio should be confirmed against the structural drawings before fabrication.
Formwork Estimating
Formwork is the largest single cost on many cast-in-place concrete jobs — often 40–60% of the total. It is also the easiest to under-estimate because it depends on exposed surface area, not concrete volume.
Slab on grade
Formwork only at the perimeter. Area = 2 × (length + width) × thickness. A 20×15 ft slab at 4 inches needs about 23 sq ft of formwork.
Strip footing
Both long sides are formed. Area = 2 × length × thickness. A 60 ft footing at 8 inches thick needs about 80 sq ft of formwork.
Column
All four sides are formed. Area = 2 × (A + B) × height. A 12×12 inch column, 10 ft tall, needs about 80 sq ft of formwork per column.
Beam
Two sides plus the bottom. Area = (length × width) + 2 × (length × depth). A 24 ft beam at 12×18 inches needs about 96 sq ft of formwork.
Worked Example — 20 ft × 15 ft Slab on Grade at 4 in
| Material | Calculation | Quantity | Cost @ reference price |
|---|---|---|---|
| Concrete volume | 20 × 15 × 0.3333 ÷ 27 | 3.70 yd³ | $592 (@ $160/yd³) |
| With 5% waste | 3.70 × 1.05 | 3.89 yd³ | — |
| Rebar (standard) | 3.89 × 60 lb/yd³ | 233 lb | $198 (@ $0.85/lb) |
| Formwork | 2 × (20 + 15) × 0.3333 | 23.3 sq ft | ~$35 (plywood) |
| Base gravel (4 in) | 20 × 15 × 0.3333 ÷ 27 | 3.70 yd³ | $100 (@ $27/yd³) |
| Total material cost | ~$925 | ||
Notice the pattern: concrete is roughly 65% of the material cost, rebar is 20%, base gravel is 10%, and formwork is under 5%. That ratio holds for most residential concrete elements, which is why small errors in concrete volume matter far more than small errors in formwork.
Concrete material standards are set by ASTM C94 (ready-mixed concrete) and ACI 318 (structural concrete design). Reinforcement follows ASTM A615 (deformed and plain carbon-steel bars), ASTM A706 (low-alloy for seismic), and BS 4449 for UK and European markets. Formwork pressure and safety follow ACI 347. Base gravel is specified under AASHTO M147 and ASTM D2940.
Concrete runs about 65% of the material cost on most residential elements. Rebar is about 20% at 60–150 lb/yd³. Base gravel adds 10% at 4 inches depth. Formwork is often the hidden cost — 40–60% of the total installed cost but only 5% of the material cost. Always add 5% waste on concrete, 10% on rebar (for cutting and lap losses), and 15% on formwork plywood (for cutting and reuse depletion).
People Also Ask
How do I estimate construction materials for a concrete slab?
Start with the slab volume: length × width × thickness (in feet) ÷ 27 gives cubic yards. Add 5% for waste. Then estimate rebar at 30–100 lb per cubic yard depending on load, formwork at the perimeter only, and base gravel at 4 inches depth under the full slab area. The calculator above runs all four in one pass.
How many pounds of rebar per cubic yard of concrete?
It depends on the element. Slab on grade: 30–100 lb/yd³. Strip footing: 60–150. Pad footing: 70–160. Retaining wall: 80–190. Column: 120–260. Beam: 100–220. Column and beam ratios are highest because they carry bending and axial load rather than just distributing it.
Should I order ready-mix concrete or bags?
Ready-mix for anything over 2 cubic yards. Bags for anything under 2 yards, or for tight-access sites where a truck cannot reach. Ready-mix runs $140–$200/yd³ delivered and arrives in 10–11 yard trucks. Bags run $6–$9 each and yield 0.6 ft³ per 80 lb bag (about 45 bags per cubic yard).
How much does a cubic yard of concrete cover?
One cubic yard (27 cubic feet) covers: 324 sq ft at 1 inch thick, 162 sq ft at 2 inches, 108 sq ft at 3 inches, 81 sq ft at 4 inches, 54 sq ft at 6 inches, or 41 sq ft at 8 inches. Divide 324 by the thickness in inches to get the coverage at any depth.
How do I estimate formwork for a concrete element?
Formwork area equals the surface area of concrete that touches the form. Slab on grade: only the perimeter edges. Strip footing: both long sides. Column: all four sides. Beam: two sides plus the bottom. A good rule is 1 sq ft of formwork for every 1 sq ft of exposed concrete surface, plus 15% for cutting waste and plywood depletion.
How much does concrete cost per cubic yard in 2026?
Ready-mix concrete runs $140 to $200 per cubic yard delivered in most US markets. The spread comes from region, mix design (3,000 psi vs 5,000 psi), aggregate availability and delivery distance. Small loads under 3 yards carry a short-load fee of $50–$150. High-strength or specialty mixes cost $40–$80/yd³ more.
What is the minimum concrete order?
Most ready-mix plants will deliver as little as 1 cubic yard, but they charge a short-load fee below 3–4 yards because the truck has to make the trip for a partial load. Some plants have a minimum of 2 cubic yards. Below 2 yards, bags are usually cheaper even with the labour of mixing on site.
How much gravel goes under a concrete slab?
The standard base is 4 inches of compacted gravel under a residential slab on grade. Soft or expansive subgrade may need 6 inches. The gravel volume equals slab area × base depth, and the weight is about 1.4 tons per cubic yard (or 2,800 lb per cubic yard for compacted 3/4-inch crushed stone).
Does the calculator include labour or equipment?
No. This estimator covers materials only — concrete, rebar, formwork and base gravel. Labour, equipment, pump truck, finishing and inspection costs are separate and can easily double or triple the total. For a rough rule, installed concrete work typically runs 2–3× the material cost in North America.
What psi concrete do I need?
For residential slabs on grade: 3,000–3,500 psi. Driveways: 3,500–4,000 psi. Footings: 2,500–3,000 psi. Columns and structural beams: 4,000–5,000 psi. Higher psi means more cement per yard and higher cost, so match the mix to the element. Always confirm with the structural drawings.
How much waste should I add to a concrete order?
5% for straightforward slabs and footings on firm subgrade. 10% for complex shapes, elevated work, or when the pump truck has to prime with a slurry that gets dumped. 15% when pouring against soil that may absorb water or when the formwork has gaps. Under-ordering means a cold joint when the second truck arrives 45 minutes late — worse than the small extra cost of over-ordering.
Can I use this estimator for a foundation, wall or column?
Yes. The calculator handles six element types: slab on grade, strip footing, pad footing, retaining wall, column and beam. Each uses the correct volume formula, formwork area rule and reinforcement ratio for that element. This is the difference between a generic volume calculator and a real material estimator — the reinforcement and formwork change significantly between a slab and a column of the same volume.
Is this calculator free and does it store my data?
Yes and no. Every calculation runs entirely in your browser — nothing is sent to a server, nothing is stored. Your inputs are not saved anywhere. The only thing remembered is the rating counter, which uses your browser's local storage and never leaves your device.
Related Calculators
References
- ASTM C94 / C94M — Standard Specification for Ready-Mixed Concrete. ASTM International.
- ACI 318 — Building Code Requirements for Structural Concrete. American Concrete Institute.
- ASTM A615 / A615M — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement. ASTM International.
- ACI 347 — Guide to Formwork for Concrete. American Concrete Institute.
- AASHTO M147 — Standard Specification for Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses. American Association of State Highway and Transportation Officials.
Confirm element dimensions, concrete strength and reinforcement details against the structural drawings and local code before ordering. Material quantities from this estimator are for planning only.