Concrete Calculator
Free concrete calculator for slabs, columns, steps, and curbs. Get instant cubic yards, bag counts (40 / 60 / 80 lb), weight, and a 2026 cost estimate. Switch between Imperial and Metric units. No sign-up.
Concrete Volume Calculator
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DIY Mix Ratio Calculator (mix your own)
For users mixing their own concrete from cement, sand, and aggregate. Standard 1:2:3 mix is fine for sidewalks and patios. Use 1:1.5:3 (structural) for footings and foundations.
- 0 bags of 94 lb Portland cement
- 0 ft³ of sand
- 0 ft³ of gravel / aggregate
- ~0 gallons of water
Note: 1 bag of Portland cement (94 lb) ≈ 1 ft³ loose volume. Water-cement ratio ~0.5 by weight.
Concrete Bag Coverage Reference
Standard pre-mixed concrete bag yields. Most US home centers carry 40, 60, and 80 lb bags. Quikrete and Sakrete follow these same coverages.
| Bag size | Volume per bag | Bags per cubic yard | Bags per cubic foot |
|---|---|---|---|
| 40 lb | 0.011 yd³ · 0.30 ft³ | 90 bags | 3.3 bags |
| 60 lb | 0.017 yd³ · 0.45 ft³ | 60 bags | 2.2 bags |
| 80 lb | 0.022 yd³ · 0.60 ft³ | 45 bags | 1.67 bags |
Common project bag counts (pre-calculated)
| Project | Dimensions | 60 lb bags | 80 lb bags |
|---|---|---|---|
| 4×4 ft sidewalk slab (4″) | 16 ft² | 4 bags | 3 bags |
| 10×10 ft patio (4″) | 100 ft² | 75 bags | 56 bags |
| 12×12 ft shed floor (4″) | 144 ft² | 108 bags | 80 bags |
| 2-car driveway (4″) | 20×20 ft | 300 bags | 222 bags |
| 6″ × 24″ deep fence-post hole | — | 1 bag | 1 bag |
| 10″ Sonotube × 3 ft deep | 1 column | 4 bags | 3 bags |
How to calculate how much concrete you need
- Measure your project — for a slab: length, width, and thickness. For a column: diameter and depth.
- Calculate volume in cubic feet — for a rectangle, multiply L × W × (T ÷ 12).
- Convert to cubic yards — divide cubic feet by 27.
- Add a waste factor — 10% for slabs, 5% for footings.
- Choose delivery — order ready-mix by the yard, or divide cubic feet by 0.6 for 80 lb Quikrete bags.
How many bags of concrete do I need?
This is the #1 question for DIY pours. The fastest formula:
Example: A 10×10 ft slab at 4 inches = 33.3 ft³ ÷ 0.6 = 56 bags of 80 lb Quikrete.
For 60 lb bags, divide by 0.45. For 40 lb bags, divide by 0.30. Always round up.
How many cubic yards of concrete do I need?
Contractors and ready-mix suppliers think in yards. The contractor formula:
Example: 20×30 ft driveway at 4″ = (20 × 30 × 4) ÷ 324 = 7.41 cubic yards. Order 8.2 yd³ including 10% waste.
Concrete slab thickness guide
| Application | Recommended thickness |
|---|---|
| Walkways / paths | 3–4 inches |
| Patios | 4 inches |
| Driveways (passenger cars) | 4–5 inches |
| Driveways (trucks / RVs) | 5–6 inches |
| Garage floors | 4–6 inches |
| Structural footings | 6–8 inches |
| Basement floors | 4 inches (with vapor barrier) |
Ready-mix vs. bagged concrete — which should you use?
- Less than 1 cubic yard (~27 ft³): use bags. Ready-mix isn't worth the short-load fee.
- 1–3 yards: borderline. Bags are doable but tedious; consider calling a local concrete plant for a small ready-mix delivery.
- More than 3 yards: always order ready-mix. Bagging this volume is backbreaking and you'll get inconsistent strength between batches.
- Cost comparison: ready-mix runs about $125–$150/yd³ delivered. 80 lb bags at $6 each = ~$270/yd³ — bags are roughly 2× the material cost, but no minimum order.
Concrete cost per yard — 2026 prices
- Ready-mix delivered: $125–$200/yd³, depending on region, mix design, and fuel surcharges.
- Short-load fee: $150–$300 if you order under ~10 yd³.
- Fiber reinforcement: +$15–$25/yd³.
- Color additive: +$15–$30/yd³.
- Accelerator (cold weather): +$10–$20/yd³.
- Pump truck: $150–$200/hour, plus ~$1/yd³ pumped.
Concrete or asphalt for a driveway?
For most US climates, asphalt is 30–50% cheaper upfront ($3–7/sqft installed vs. $6–10/sqft for concrete) and handles freeze-thaw better, while concrete lasts 25–30 years and resists summer heat. If you're weighing the alternative, our asphalt calculator gives tonnage, cost, and the right thickness in seconds.
The difference between concrete and cement
People use the words interchangeably, but they aren't the same. Cement is the powdered binder — Portland cement, made by heating limestone and clay. Concrete is the finished material: cement (about 10–15%), sand, gravel/aggregate (60–75%), and water (15–20%) mixed together. You don't pour cement; you pour concrete.
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