Concrete Calculator for Volume and Cost
Concrete Calculator
Concrete Volume Calculator
Slabs, Square Footings, or Walls
Slabs, Square Footings, or Walls - Results
Concrete Settings
The concrete calculator computes how many cubic yards (or cubic meters) of concrete you need for a slab, footing, column, or other structure. It handles rectangular slabs, round columns, stairs, and curbs. Accurate concrete estimation prevents costly over-ordering (concrete trucks charge for unused material and return trips) or under-ordering (running short mid-pour can create cold joints that weaken the structure).
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Concrete Volume Calculation
Concrete is ordered in cubic yards in the US. The basic calculation is length × width × depth, all in feet, divided by 27 (since 1 cubic yard = 27 cubic feet). Always convert depth to feet first: a 4-inch slab is 4/12 = 0.333 feet deep. Add a 5-10% waste factor for irregular shapes, settling, and spillage.
Slab: Volume (cu yd) = Length(ft) × Width(ft) × Depth(ft) / 27 Round column: Volume = π × r²(ft) × Height(ft) / 27 Footing (rectangular): same as slab formula Example: 10×12 ft slab at 4 inches depth: = 10 × 12 × (4/12) / 27 = 40/27 = 1.48 cu yd Order 1.6 cu yd (adding 8% waste)
1 cubic yard of concrete weighs approximately 4,000 lbs and covers 81 sq ft at 4 inches depth.
Concrete Mix Ratios (DIY)
The three primary ingredients in concrete are Portland cement, sand (fine aggregate), and gravel or crushed stone (coarse aggregate). The ratio affects strength, workability, and cost. Higher cement content increases strength but also shrinkage cracking risk. For most DIY projects, pre-bagged concrete mix is easier than proportioning components separately.
| Application | Mix Ratio (cement:sand:gravel) | Typical Strength |
|---|---|---|
| General purpose slab | 1:2:3 | 2,500-3,000 psi |
| Driveways | 1:2:2 | 3,000-3,500 psi |
| Foundations | 1:1.5:3 | 3,000 psi |
| Paths and patios | 1:2:3 | 2,500 psi |
| High-strength structural | 1:1.5:2.5 | 4,000+ psi |
| Fence posts (pre-mix) | As packaged | 4,000 psi (Quikrete 5000) |
Pre-Mixed Bags vs Ready-Mix Truck
For projects under about 0.5 cubic yards (approximately 14 bags of 60-lb mix), pre-bagged concrete from a hardware store is most practical. Above that volume, ordering a ready-mix truck becomes cost-competitive once you factor in labor time mixing bags. One 60-lb bag of pre-mix makes about 0.45 cubic feet; one 80-lb bag makes about 0.60 cubic feet. Most concrete trucks have a minimum order of 1 cubic yard, and suppliers typically charge a short-load fee for less than 5-7 yards.
| Volume Needed | Best Option | Notes |
|---|---|---|
| Under 0.5 cu yd | Pre-mixed bags (60-80 lb) | 14-18 bags of 60-lb or 11-14 bags of 80-lb |
| 0.5-1 cu yd | Pre-mix bags or mixer rental | Consider renting a cement mixer for consistency |
| 1-3 cu yd | Ready-mix truck (min order) | Short-load fee often applies |
| Over 3 cu yd | Ready-mix truck | Most cost-effective, consistent mix quality |
Concrete Curing and Strength
Concrete does not "dry" — it cures through a chemical hydration reaction between water and cement. This process generates heat and continues for months, but most practical strength is gained in the first 28 days. Cold weather slows curing and requires protection; freezing concrete before it has gained sufficient strength can permanently damage the structure. Hot, dry weather speeds surface drying too fast and requires misting and covering to prevent cracking.
Concrete strength gain over time: Day 1: ~15% of 28-day strength Day 3: ~40% Day 7: ~65-70% Day 14: ~90% Day 28: 100% (design strength)
Foot traffic: safe after 24-48 hours. Vehicle traffic: wait at least 7 days. Full design load: 28 days.
Frequently Asked Questions
How thick should a concrete slab be?⌄
Thickness depends on the load the slab will carry. Residential driveways: 4 inches minimum, 5 inches if heavy vehicles (delivery trucks, RVs) use it. Patios and walkways: 3-4 inches. Garage floors: 4-6 inches. Structural foundations and footings: 6-8 inches minimum, or per engineering specifications. Footings for fence posts: 12+ inches deep (below frost line in cold climates). When in doubt, thicker is better — the incremental cost of extra concrete is small compared to the cost of a cracked slab.
Should I use ready-mix or DIY concrete?⌄
Ready-mix from a concrete truck is best for large pours above 0.5 cubic yards because it saves labor, ensures consistent mix quality, and completes the pour faster (minimizing cold joint risk). Pre-mixed bags (Quikrete, Sakrete, Maximizer) work well for small projects. One 60-lb bag covers about 0.45 cubic feet; one 80-lb bag about 0.60 cubic feet. Hand mixing is feasible up to about 10-15 bags; above that, rent a cement mixer for consistent results.
How long does concrete take to cure?⌄
Concrete reaches about 65-70% of its design strength by day 7 and full strength at 28 days. You can typically walk on a slab after 24-48 hours (longer in cold weather below 50°F). Do not drive vehicles on a slab for at least 7 days. For heavy structural loads or machinery, wait the full 28-day cure period. Keep newly poured concrete moist by misting with water or covering with wet burlap for the first 7 days — this prevents premature drying and significantly improves final strength.
Do I need a permit for a concrete slab?⌄
Permit requirements vary by municipality. Many areas require permits for slabs attached to a structure, slabs above a certain size (often 200 sq ft or more), any concrete foundation, and driveways that connect to a public street. Small decorative patios and garden paths typically do not require permits in most jurisdictions. Check with your local building department or permit office before starting. Unpermitted concrete work can complicate home sales, insurance claims, and future renovation permits.
Can I pour concrete in cold weather?⌄
Yes, with precautions. Concrete should not be poured when temperatures will fall below 40°F (4°C) within the first 24-48 hours unless protective measures are taken. At low temperatures, hydration slows dramatically. Frozen concrete before it reaches adequate strength is permanently weakened. Cold weather precautions include using heated water in the mix, covering fresh concrete with insulating blankets, and using accelerating admixtures (calcium chloride can reduce cure time by 30-50% in cold conditions). Avoid pouring on frozen ground.