Concrete Calculator
🧱 Concrete Calculator
Concrete slab calculator, concrete bag calculator, and concrete yard calculator in one tool — with step-by-step math.
✅ Planning estimate only. Always round up and confirm bag yield/ready-mix minimums with your supplier.
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🧮 Calculation steps (your values)
- Enter your dimensions, then click Calculate.
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Concrete Calculator FAQs
These FAQs are general guidance. For exact ordering rules, confirm with your local supplier.
Q1: How much concrete do I need for a 10×10 slab?
A 10×10 ft slab that’s 4 in thick needs about 33.3 ft³ of concrete. That’s 33.3 ÷ 27 = 1.23 yd³ (cubic yards). With a typical 10% waste factor, order about 1.36 yd³. (Always round up to what your supplier can deliver—many deliver in 0.25 yd increments.)
Q2: How do I calculate concrete in cubic yards from feet and inches (with steps)?
Use this quick method: (1) Convert thickness from inches to feet: in ÷ 12. (2) Compute volume in cubic feet: Length(ft) × Width(ft) × Thickness(ft). (3) Convert to cubic yards: ft³ ÷ 27 = yd³. Example: 12 ft × 10 ft × (4 in ÷ 12) = 40 ft³ → 40 ÷ 27 = 1.48 yd³ (then add 5–15% waste if needed).
Q3: How many 80lb bags of concrete are in one cubic yard?
One cubic yard is 27 ft³. An 80lb bag yields roughly 0.60 ft³, so 27 ÷ 0.60 ≈ 45 bags per cubic yard. Bag yields vary slightly by brand (including popular mixes like Quikrete), so treat this as an estimate and keep a couple of extra bags for small jobs.
Q4: How many bags of concrete do I need for 100 square feet at 4 inches thick?
100 sq ft × 4 in thick = 100 × (4 ÷ 12) = 33.3 ft³.
Approximate bag counts (before waste):
80lb bags: 33.3 ÷ 0.60 ≈ 56 bags
60lb bags: 33.3 ÷ 0.45 ≈ 74 bags
Add 5–10% for waste (and round up to whole bags).
Q5: How much concrete do I need for a 12×12 slab at 4 inches thick?
Convert thickness: 4 in = 0.333 ft. Volume = 12 × 12 × 0.333 = 48 ft³. That’s 48 ÷ 27 = 1.78 yd³. With 10% waste, order about 1.96 yd³ (often rounded to 2.0 yd³ depending on supplier increments and site conditions).
Q6: How do I calculate concrete for a round slab or circular column?
Use the cylinder formula: Volume = π × (Diameter ÷ 2)² × Height/Thickness. Keep units consistent. Example (round slab): 10 ft diameter, 4 in thick → radius = 5 ft; thickness = 0.333 ft. Volume = 3.1416 × 25 × 0.333 ≈ 26.2 ft³ = 0.97 yd³ (then add waste).
Q7: What waste factor should I add when ordering concrete (ready-mix or bags)?
Common guidance is:
5% for simple pours with level subgrade and tight forms
10% for typical residential slabs, walkways, and driveways
10–15% for irregular shapes, uneven excavation, beginners, or hard-to-reach placement
If you’re ordering ready-mix, it’s usually safer to round up slightly to avoid running short mid-pour (cold joints can weaken the finished work).
Q8: Should I use bagged concrete or ready-mix concrete for my project?
A practical rule:
Bagged concrete works best for small pours (often under ~0.5–0.75 yd³) like fence posts, small pads, small repairs.
Ready-mix is usually better for ~1 yd³ or more (patios, driveways, larger slabs) because it’s faster, more consistent, and often cheaper per cubic yard once you factor in labor/time.
Also consider access: if a truck can’t get close, you may need a pump or many wheelbarrow trips.
Q9: How much does concrete cost per cubic yard (and what affects price)?
In many areas, ready-mix concrete commonly ranges from $125 to $200+ per yd³ (delivery and minimum-load fees may apply). Installed costs (with labor, forming, base prep, finishing) can be much higher and vary by region and site complexity. Price depends on mix strength (psi/MPa), distance to plant, short-load fees, additives (fiber, accelerator/retarder), reinforcement, and finishing type (broom vs stamped).
Q10: What is the M20 concrete mix ratio (1:1.5:3), and how much cement do I need for 1 m³?
M20 is often shown as a nominal 1:1.5:3 ratio (cement:sand:aggregate) and is commonly used for many residential applications (where permitted by local codes/specs). A widely used estimating reference for 1 m³ of M20 is about: Cement ~403 kg, Sand ~604 kg, Aggregate ~1,208 kg, Water ~181 L (actual requirements vary with moisture, aggregate size, and design mix specs). For structural work, follow engineered mix designs and local standards rather than nominal ratios.
Q11: How many 50kg bags of concrete mix make 1 cubic meter (1 m³)?
A 50kg bag of concrete mix typically yields about 0.017 m³ (varies by brand). So 1 m³ ÷ 0.017 ≈ 58 bags. Use this as an estimate and confirm the yield printed on your specific bag.
Q12: How do I use the “US” vs “Others” tabs in this concrete calculator?
Use US if you’re ordering in cubic yards (yd³) and estimating typical 40/60/80 lb bags and US-style rounding (often 0.25 yd³ increments). Use Others if you prefer cubic meters (m³) and common 25kg/50kg bag estimates. Regardless of the tab, you can still enter dimensions in ft/in/m/cm/mm using the unit dropdown beside each field.
Q13: Can I enter thickness in centimeters or millimeters instead of meters (or inches)?
Yes. Use the unit dropdown beside the thickness field (and any dimension field) to select cm or mm if the value is small. This helps avoid mistakes like entering 0.10 m when you meant 10 cm, or entering 0.04 m when you meant 4 cm.
Q14: How do I estimate cement, sand, and aggregate for a custom mix ratio (like 1:2:3)?
Choose Custom ratio and enter cement:sand:aggregate “parts” (e.g., 1 : 2 : 3). The calculator then divides the total concrete volume into those parts (using standard estimating assumptions such as a dry-volume factor) to estimate cement (kg/bags), sand, aggregate, and water. This is for planning only—structural work should follow supplier or engineer mix specifications.
References & Industry Standards Used in This Calculator
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These sources explain concrete basics and typical estimating guidance.
- American Cement Association (PCA) – Cement & Concrete Basics, Applications, and Industry Standards
- American Concrete Institute (ACI) – Concrete Design Codes, Standards, and Technical Guidelines
- QUIKRETE Calculator – Concrete Quantity Calculator and Material Coverage Estimation
- The Concrete Network – Concrete Coverage Calculations and Estimation Methods
- Concrete Construction Best Practices and Guidelines (PDF)
Methodology (How This Calculator Works)
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1) Base volume
- Slab/footing: length × width × thickness
- Column: π × r² × height
- Stairs: triangular solid approximation
2) Unit conversions
- 1 yd³ = 27 ft³
- 1 ft³ = 0.0283168 m³
- Each dimension supports ft/in/m/cm/mm (selected beside the input)
3) Wastage and bag estimates
- Adjusted volume = base × (1 + wastage%/100)
- Bag yields are approximate and vary by product, water content, and brand; always confirm the bag label
- Suggested order rounds up (US: commonly 0.25 yd³; Others: commonly 0.05 m³)
4) Mix ratio (optional)
- Preset ratios (e.g., M20 = 1:1.5:3) and custom ratios are for estimating only (not a strength guarantee).
Rectangular slab/footing: V(ft³) = L(ft) × W(ft) × T(ft) Circular column: V(ft³) = π × r² × h Stairs (solid approximation): V(ft³) = (steps × tread(ft) × riser(ft) × width(ft)) ÷ 2 Conversions: yd³ = ft³ ÷ 27 m³ = ft³ × 0.0283168 Wastage: V_adj = V_base × (1 + waste%/100)
