Concrete Slab, Yardage, Bag & Cost Calculator
Use this highly optimized concrete calculator to determine volume, bags needed, weight, and price estimate for your project.
Project Settings & Contingency Margin
Standard 80lb bag yields 0.6 cu. ft. of concrete volume.
Used for concrete price calculator estimate.
Extra material for grade errors, spillage, etc.
Concrete Calculation Results (Including Contingency)
Please ensure all required fields have valid, positive values before calculating.
Concrete Calculator — Estimate Volume, Bags, Weight & Cost
Use FitForYard’s professional concrete calculator guide to estimate how much concrete you need for slabs, footings, driveways and post-holes. Includes simple formulas, step-by-step examples, bag and ready-mix estimates, weight and cost guidance — optimized for both homeowners and contractors.
Quick answer — How to calculate concrete
Measure Length × Width × Depth (all in feet) to get cubic feet. Then convert to cubic yards by dividing cubic feet by 27. Example: 10 ft × 10 ft × (4 in → 0.333 ft) = 33.33 ft³ → 33.33 ÷ 27 ≈ 1.23 cubic yards.
What is a concrete calculator?
A concrete calculator is a tool or guide that helps you convert project dimensions into the volume of concrete needed (usually in cubic yards), and then into bags or cost estimates. It handles shapes like slabs, pads, footings, cylinders (post holes) and walls.
Why use a concrete calculator?
- Avoid under-ordering or over-ordering concrete (save money and time).
- Plan deliveries and truck logistics using weight estimates.
- Compare bagged concrete vs. ready-mix pricing for smaller and larger jobs.
- Include a contingency margin to prevent shortages on pour day.
Core formulas & unit conversions (keep these handy)
Basic volume formula (all shapes)
Volume (cubic feet) = Length (ft) × Width (ft) × Depth (ft)
Convert to cubic yards: Cubic Yards = Cubic Feet ÷ 27
Common constants & yields
- 1 cubic yard = 27 cubic feet.
- Typical 80 lb bag yield ≈ 0.6 cubic feet of concrete (common Quikrete / bagged mixes). See product specifics on labels for exact yield.
- Typical 60 lb bag yield ≈ 0.45 cubic feet.
- Weight: one cubic yard of concrete ≈ 4,000 pounds (about 2 US tons) — varies slightly by mix and moisture content.
Which concrete calculators are included
This guide covers:
- Concrete slab calculator (patios, pads, driveways)
- Concrete footing / stem wall calculator
- Post-hole / cylinder (Sonotube) calculator
- Bagged concrete calculator (80 lb / 60 lb bags)
- Concrete weight & transport planning
- Concrete cost & price calculator (ready-mix vs bagged)
How to calculate concrete for a slab (step-by-step)
Follow these steps for a rectangular slab (patio, garage pad, small driveway):
- Measure Length (ft), Width (ft) and Thickness (inches).
- Convert thickness to feet: Thickness (in) ÷ 12 = Depth (ft).
- Compute volume in cubic feet: Length × Width × Depth (ft).
- Convert cubic feet → cubic yards: divide by 27.
- Round up and add contingency (5–10%) for waste and spillage.
Example: 10 ft × 10 ft slab at 4 in thickness
Depth = 4 ÷ 12 = 0.333 ft.
Volume (ft³) = 10 × 10 × 0.333 = 33.33 ft³.
Volume (CY) = 33.33 ÷ 27 = 1.23 cubic yards.
Tip: Add 5–10% contingency. For 1.23 CY, add 10% → 1.35 CY to order.
Calculating concrete for footings and walls
Footings are typically rectangular. Convert width and height from inches to feet, then multiply by length (ft) to get cubic feet, then divide by 27 for cubic yards.
Steps:
- W (in) ÷ 12 = W (ft); H (in) ÷ 12 = H (ft).
- Volume (ft³) = Length (ft) × W (ft) × H (ft).
- Volume (CY) = Volume (ft³) ÷ 27.
Post hole (cylinder) calculation — Sonotube & fence posts
For circular holes use cylinder volume formula (in feet):
Radius (ft) = (Diameter (in) ÷ 2) ÷ 12
Volume (one hole, ft³) = π × Radius² × Depth (ft)
Total Volume = Volume(one hole) × Number of holes → convert ft³ ÷ 27 for cubic yards.
Example: 12 in diameter × 3 ft deep post hole
Radius = (12 ÷ 2) ÷ 12 = 0.5 ft.
Volume (one) = 3.1416 × 0.5² × 3 ≈ 2.356 ft³.
Total for 4 holes = 2.356 × 4 = 9.425 ft³ → 9.425 ÷ 27 = 0.349 CY.
Bagged concrete vs. ready-mix — when to buy which
Bagged concrete (80 lb / 60 lb): Best for small projects (< 2 cubic yards) or repairs. Easier for DIY; increases labor time for mixing.
Ready-mix by the yard: Best for larger pours — more economical (per yard) and faster for contractors. Typical minimum order or small-load fees may apply.
How many 80 lb bags for that 10×10×4 in slab?
1 standard 80 lb bag ≈ 0.6 ft³ of finished concrete (check bag label).
Total volume = 33.33 ft³ ÷ 0.6 ≈ 55.55 → round up = 56 bags.
Note: Bag yields vary by bag type and moisture; always verify the manufacturer’s yield on the product label.
Concrete cost calculator — October 2025 USA price guide
Concrete prices vary by region, PSI, additives, delivery distance and truck type. Use local supplier quotes for exact pricing. Typical October 2025 USA price ranges (material only) are:
- Standard ready-mix concrete: approximately $110 – $150 per cubic yard.
- Higher-strength or specialty mixes (e.g., 4,000 PSI, fiber, color): $150 – $180+ per cubic yard depending on options.
- Delivery / small-load fees: many suppliers add a small-load or delivery fee, and truck/volume surcharges (typical delivery costs may be $20–$50+ per yard or a flat small-load fee).
- 80 lb bag (retail) price: varies by retailer and region — typical retail range is ~$4–$7 per 80 lb bag (check current local store pricing).
How to estimate project cost
- Calculate required cubic yards (see examples above).
- Multiply cubic yards by local ready-mix price per CY.
- If using bags: calculate number of bags × retail price per bag.
- Add contingency (5–10%) + delivery and labor if applicable.
Cost example
Using our 10×10×4 in slab example (1.23 CY):
- If ready-mix is $130/CY: Material cost = 1.23 × $130 ≈ $160.
- If ordering bags and retail is $5.50 per 80 lb bag: 56 bags × $5.50 = $308 (material only).
Conclusion: For small DIY slabs, bagged concrete can be convenient but often more expensive per yard. For larger pours, ready-mix is usually cheaper overall and faster.
Weight planning & truck logistics
Use weight to plan truck capacity and site access. A rough planning number: one cubic yard ≈ 4,000 lb (about 2 US tons). Multiply by total CY ordered to estimate loaded weight and trucking needs.
Example: 5 CY ≈ 5 × 4,000 = 20,000 lb (≈ 10 tons) — confirm local truck limits and permit needs for heavy loads.
Contingency: why you should order extra
Always add a contingency margin (typically 5–10%) for spillage, uneven subgrade, over-excavation and finish adjustments. For complex sites or poor access, consider 10%+ depending on risk.
Use FitForYard’s Online Concrete Calculator
For instant estimates, use our interactive Concrete Calculator tool. It converts dimensions to cubic yards, bag counts and cost estimates, and includes contingency and delivery options.
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Frequently Asked Questions (FAQs)
Q: How do I calculate yards of concrete?
A: Multiply Length × Width × Depth (in feet) to get cubic feet, then divide by 27 to convert to cubic yards. Always add 5–10% contingency before ordering.
Q: How many 80 lb bags of concrete do I need for a 10×10 slab at 4 inches?
A: The 10×10×4 in slab uses ~33.33 ft³. With an 80 lb bag yield of ~0.6 ft³: Bags = 33.33 ÷ 0.6 ≈ 55.55 → round up to 56 bags (always verify bag yield).
Q: What does one cubic yard of concrete weigh?
A: Approximately 4,000 lb per cubic yard (about 2 US tons), though the exact weight depends on mix, aggregate and moisture.
Q: How much does ready-mix concrete cost?
A: National averages for October 2025 place standard ready-mix around $110–$150 per cubic yard; specialty or high-strength mixes often run $150–$180+ per yard. Always confirm local supplier pricing and delivery fees.
Q: Is it cheaper to use bags or order ready-mix?
A: For very small jobs (< ~2 CY), bags can be practical. For larger jobs (≥ 2–3 CY), ready-mix is usually more cost-effective per cubic yard and reduces labor time. Include delivery and small-load fees when comparing.
Q: Can I use this tool for driveways and foundations?
A: Yes — for driveways and foundations follow the slab or footing steps, choose the appropriate thickness (driveways commonly 6 in for residential) and add contingency. For structural foundations consult an engineer for reinforcement and PSI specifications.
Q: How do I calculate concrete for a post hole?
A: Convert diameter to radius in feet, compute cylinder volume (π × r² × depth), multiply by the number of holes, then convert cubic feet to cubic yards (÷27).
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Conclusion — Calculate concrete with confidence
FitForYard’s concrete calculator guide covers volume formulas, bag estimates, weight planning and realistic October 2025 USA price ranges. Use exact local supplier quotes for final ordering, add 5–10% contingency, and choose ready-mix for larger projects to save money and time.
Ready to calculate? Open FitForYard Concrete Calculator — enter your dimensions and get yardage, bags and quick cost estimates.