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Concrete Calculator

Estimate concrete volume in cubic yards or meters for slabs, footings, columns, and stairs; calculate bags or truck delivery.

LIFESTYLE

Estimate concrete volume in cubic yards or cubic meters for slabs, footings, round columns, and stairs.

Four shape modes with US/Metric unit toggle. Concrete bag calculator outputs counts for 60-lb (0.45 cubic feet) and 80-lb (0.60 cubic feet) bags, plus an automatic recommendation to switch to ready-mix truck delivery when volume exceeds 1 cubic yard. Includes a 0 to 20% waste factor slider.

Disclaimer: Always order 5 to 10% extra concrete to account for spillage, settling, and uneven subgrade. For structural slabs, footings, or walls, consult a licensed contractor and verify local PSI requirements (typically 3000 to 5000 PSI).

Concrete Calculator 2026

Estimate cubic yards (or cubic meters) of concrete needed for slabs, footings, columns, and stairs. Includes waste factor, bag count for 60-lb and 80-lb bags, and ready-mix truck cost guidance.

Flat rectangular pour like a patio, driveway, garage floor, or sidewalk. Volume = Length x Width x Thickness.

10%
Concrete suppliers recommend 5-15%. 10% is typical for slabs; bump to 15% for irregular footings or sloped sites.
Total Concrete Needed
0.00 cubic yards
Approximate equivalent: 0.00 cubic feet - 0.000 cubic meters
cubic yards - breakdown
Base Volume0.00 cubic yards
Waste Allowance (10%)0.00 cubic yards
Total Concrete Needed0.00 cubic yards
Bag Mix Option
60-lb bags (0.45 cu ft each)0
80-lb bags (0.60 cu ft each)0
Cost using 60-lb bags$0
Cost using 80-lb bags$0
Ready-Mix Truck Option
Volume Ordered1.00 cubic yards(min)
Estimated Truck Cost$200
RecommendationBags
Bags are practical at this volume - manageable to mix on-site.
Crossover point: about 1 cu yd (~27 cu ft / 60 bags of 80-lb).
Concrete Planning Guide
Bags vs Ready-Mix Truck
Use bagged concrete (60-lb or 80-lb) for jobs under about 1 cubic yard - small footings, fence posts, repair patches. Beyond that, hand-mixing becomes exhausting and inconsistent. Order from a ready-mix truck for slabs, driveways, and any pour above 1 cu yd. Most ready-mix companies have a 1 cu yd minimum and charge a short-load fee for orders under 3 cu yd.
PSI Strength Ratings (US)
3000 PSI: residential slabs, sidewalks, driveways. 4000 PSI: garage floors, foundations, light commercial. 5000 PSI: heavy industrial, structural columns, freeze-thaw zones. Always match PSI to load and climate - a 5000 PSI mix in a freeze region pays for itself in years of crack-free service.
Standard Mixing Ratio
A typical 4000 PSI mix is 1 part cement : 2 parts sand : 3 parts gravel by volume, with about 0.5 parts water (water-to-cement ratio of 0.50). Less water = stronger but harder to place. Bagged concrete already has cement, sand, and aggregate pre-mixed; you just add water per the bag instructions.
Curing Time
Concrete reaches about 70% of design strength at 7 days and 99% at 28 days. Keep the surface damp for at least 7 days (cover with plastic, wet burlap, or apply curing compound). Light foot traffic OK after 24-48 hrs. Vehicle traffic after 7 days. Heavy loads only after full 28-day cure.
Why a Waste Factor Matters
Real pours never match the napkin math: forms bow outward, subgrade is uneven, some concrete sticks to the wheelbarrow, and you cannot order partial bags or partial yards. Always add 10% (15% for footings or rough subgrade) - running short mid-pour means a cold joint, which weakens the structure.
Estimates only. Confirm volume with your concrete supplier before ordering, especially for structural pours. Local codes may dictate minimum thickness, PSI, and rebar requirements.

Calculator information

How to use this calculator

  1. Select shape: Slab (rectangular flat surface), Footing (linear trench), Column (cylindrical pier), or Stairs (multi-step).
  2. Choose units: US (feet/inches/cubic yards) or Metric (meters/centimeters/cubic meters).
  3. For slab: enter length, width, thickness (typical 4 inch / 10 cm for patios, 6 inch / 15 cm for driveways).
  4. For column: enter diameter and height; for stairs: tread depth, riser height, width, number of steps.
  5. Apply waste factor 5-10% for simple slabs, 10-15% for footings/columns, 15-20% for irregular shapes.
  6. Tip: Above 1 cubic yard (~0.76 m3), order ready-mix delivery (cheaper per yard); below, use bagged concrete (60 lb yields 0.45 ft3, 80 lb yields 0.6 ft3).

Concrete Volume by Shape

Slab: V = L x W x T; Column: V = pi x r^2 x h; Stairs: V = W x sum(tread x riser, accumulating)
  • L, W, T: length, width, thickness (consistent units)
  • r: radius = diameter/2
  • h: height of column
  • Conversion: 1 cubic yard = 27 cubic feet = 0.7646 cubic meters
  • Bag yield: 60 lb bag = 0.45 ft3 (0.0127 m3); 80 lb bag = 0.6 ft3 (0.017 m3)
  • Waste factor: typically 5-20% added to net volume

Ready-mix trucks typically require a minimum 1 cubic yard order. Below the threshold (often <3 yd3) you'll pay a short-load fee. Concrete settles about 5% on placement.

Worked example: Concrete Driveway Slab 20 ft x 12 ft x 6 inch

Given:
  • Length 20 ft, Width 12 ft, Thickness 6 inch (0.5 ft)
  • Reinforced with wire mesh (standard residential driveway)
  • Waste factor 10%
  • Comparing bagged vs ready-mix
Steps:
  1. Volume: 20 x 12 x 0.5 = 120 ft3
  2. Convert to cubic yards: 120 / 27 = 4.44 yd3
  3. Apply 10% waste: 4.44 x 1.10 = 4.89 yd3 (round to 5 yd3)
  4. Ready-mix cost estimate at $130/yd3 (US 2025 average): 5 x $130 = $650 plus delivery $80-150 = ~$750 total
  5. If bagged 80-lb: 120 ft3 / 0.6 ft3 per bag = 200 bags, plus 10% = 220 bags
  6. At $5.50/bag: 220 x $5.50 = $1,210 plus mixing labor/equipment
  7. Bagged is ~60% more expensive AND requires far more labor for 5 yd3 project

Result: 5 cubic yards ready-mix recommended at ~$750 vs ~$1,200 for bagged. Always order ready-mix for slabs over 1 yd3.

Frequently asked questions

How many 80-lb bags of concrete in a cubic yard?
Each 80-lb bag of pre-mixed concrete yields approximately 0.6 cubic feet when set. One cubic yard = 27 cubic feet, so 27 / 0.6 = 45 bags per cubic yard. For 60-lb bags (0.45 ft3 yield), it takes 60 bags per cubic yard. Always add 5-10% waste. For projects exceeding 1 cubic yard, ready-mix delivery is more economical and consistent than mixing dozens of bags manually.
What thickness of concrete do I need?
Standard residential thicknesses: 4 inches (10 cm) for patios, walkways, and indoor floors; 5-6 inches (12-15 cm) for driveways supporting cars and light trucks; 6-8 inches (15-20 cm) for heavy vehicles, RVs, or shop floors. Footings: 8-12 inches (20-30 cm) typical for residential foundations. Always check local building codes and frost depth (footings must be below frost line, often 12-48 inches in cold climates).
How much waste should I add to my concrete order?
Standard waste factors: 5-10% for simple rectangular slabs (spillage, slight over-pour), 10-15% for footings and complex shapes (forms not perfectly tight), 15-20% for stairs, curved walls, or projects with significant cuts. Ready-mix trucks must be fully discharged within ~90 minutes of mixing, so under-ordering is worse than over-ordering. Excess wet concrete is wasted (you cannot return it).
What is the difference between concrete and cement?
Cement (typically Portland cement) is the binder powder. Concrete is the finished material: cement + aggregate (sand and gravel) + water. Mortar is cement + sand + water (no gravel), used for bricklaying. Standard concrete mix is roughly 1 part cement : 2 parts sand : 3 parts gravel : 0.5 parts water by volume. Pre-mixed bags contain all dry components - you just add water.
How long does concrete take to cure?
Concrete reaches initial set in 4-8 hours, walkable in 24-48 hours, and 70% of full strength in 7 days. Full design strength (28-day compressive strength, typically 3,000-4,000 psi for residential) is achieved at 28 days. Heavy vehicle traffic should wait 7+ days. Curing temperature matters: below 50 deg F (10 deg C) curing slows significantly; above 90 deg F (32 deg C) concrete dries too fast and may crack. Keep moist for first 7 days for optimal strength.

Last updated: May 11, 2026

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