Concrete Calculator — How Much Concrete Do I Need?
Calculate the volume, weight, bags, and cost of concrete for your project. Select a shape mode below, enter your dimensions, and get instant results. Supports slabs, footings, columns, and more.
Concrete Calculator
Concrete Thickness Guide
| Application | Inches | Centimeters |
|---|---|---|
| Walkway / path | 4 in | 10 cm |
| Patio | 4 in | 10 cm |
| Driveway (residential) | 5–6 in | 13–15 cm |
| Garage floor | 6 in | 15 cm |
| Driveway (heavy vehicles) | 8+ in | 20+ cm |
| Foundation / footing | Per engineer spec | |
How Much Concrete Do I Need?
- Measure length and width in feet. For irregular shapes, break into rectangles and calculate each separately.
- Determine depth in inches. Standard: 4″ for walkways, 6″ for driveways.
- Calculate volume: L × W × (depth ÷ 12) = cubic feet. Divide by 27 for cubic yards.
- Calculate weight: Multiply cubic feet by 150 lb/cu ft for total weight.
- Add 5–10% for waste — uneven subgrade, spillage, and form bulges always consume extra material.
Imperial example: A 10 × 10 ft patio, 4 inches deep: 10 × 10 × (4/12) = 33.3 cu ft ÷ 27 = 1.23 cubic yards. With 10% waste: order 1.36 cubic yards.
Metric example: A 3 m × 3 m patio, 10 cm thick: 3 × 3 × 0.10 = 0.9 m³ (1.18 cu yd). At 2,400 kg/m³ = ~2,160 kg (2.16 tonnes). With 10% waste: order 0.99 m³.
Bags vs Ready-Mix Delivery
| Method | Best For | Cost/cu yd | Yield per bag |
|---|---|---|---|
| 80 lb / 36 kg bags | Small projects (< 1 cu yd / 0.76 m³) | ~$225–$315 /yd³ (~$294–$412 /m³) | 0.6 cu ft (0.017 m³) / bag |
| 60 lb / 27 kg bags | Easier to handle | ~$240–$300 /yd³ (~$314–$392 /m³) | 0.45 cu ft (0.013 m³) / bag |
| 25 kg bags (EU/AU) | Metric markets | local pricing varies | 0.012 m³ (0.42 cu ft) / bag |
| Ready-mix truck | Projects > 1 cu yd / 0.76 m³ | $150–$200 /yd³ ($196–$262 /m³) | n/a (bulk delivery) |
Ready-mix delivery typically includes a $50–$100 delivery fee with a minimum order of 1 cubic yard. The break-even point is around 1 cubic yard — above that, ready-mix is cheaper than bags.
Curing and Strength
Concrete reaches approximately 70% of its final strength in 7 days and typically achieves its target design strength in 28 days. Standard pre-mixed bags (e.g., Quikrete, Sakrete) are commonly rated at 4,000 PSI at 28 days, though actual strength depends on mix design, water ratio, and curing conditions. Proper curing is essential:
- Keep wet for the first 7 days — mist or cover with plastic sheeting to retain moisture.
- Temperature matters: below 50°F slows curing significantly. Above 90°F can cause rapid surface drying and cracking.
- Don’t load too early: foot traffic after 24–48 hours, vehicles after 7 days minimum.
Frequently Asked Questions
How many bags of concrete do I need for a 10×10 slab?
At 4 inches thick: 10 × 10 × 0.333 = 33.3 cu ft ÷ 0.6 cu ft per bag (80 lb) = 56 bags. At 6 inches thick: 50 cu ft ÷ 0.6 = 84 bags. Always add 10% for waste.
How much does a yard of concrete cost?
$150–$200 per cubic yard for ready-mix delivery (2026 US average). Bagged concrete costs approximately $225–$315 per cu yd using 80 lb bags at $5–$7 each (45 bags per yard) — suitable for small projects under 1 cubic yard.
Can I pour concrete in the rain?
Light rain: yes, but cover the surface immediately after finishing. Heavy rain: no — excess water dilutes the cement paste, weakens the mix, and can cause surface scaling and reduced strength.
What is a common concrete mix ratio?
A common nominal mix ratio is 1 part cement : 2 parts sand : 3 parts gravel (1:2:3) by volume, widely used for general-purpose applications. Pre-mixed bags (80/60/40 lb) already contain the correct ratio — just add water per the bag instructions.
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Concrete density: 150 lb/cu ft (ACI 211.1 standard for normal-weight concrete). Bag yields: 80 lb = 0.6 cu ft, 60 lb = 0.45 cu ft, 40 lb = 0.3 cu ft. Sources: ASTM C94 (ready-mix spec), Portland Cement Association, ACI 318 (building code). Prices are 2026 US national averages.