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Concrete Volume Calculator

Calculate concrete volume in cubic yards and pre-mix bag counts (80 lb & 60 lb) for slabs, footings, and stairs. Includes 10% waste buffer.

Concrete to Order (Cubic Yards)
0.5228yd³
Total Cubic Feet (with waste)14.117 ft³
80 lb Pre-Mix Bags (yield ~0.60 ft³ each)24 bags bags
60 lb Pre-Mix Bags (yield ~0.45 ft³ each)32 bags bags
Cubic Meters (Metric)0.3997 m³
3D Geometric Profile
Step 1: Calculate Stair Profile Staircase Area3.2083 ft²
Formula: A_profile = Rise × Run × [n × (n + 1) / 2]
Substitution: 0.5833 ft × 0.9167 ft × [3 × 4 / 2] = 3.2083 ft²

Computes the tiered stepped profile cross-section for the solid monolithic concrete pour.

Step 2: Multiply by Stairway Width12.833 ft³
Formula: V = A_profile × Width
Substitution: 3.2083 × 4 = 12.833 ft³

Total solid concrete needed for the stairway.

Step 3: Convert to Cubic Yards and Add 10% Safety / Spillage Allowance0.5228 yd³
Formula: Yards = (V_ft3 / 27) × (1 + Waste%)
Substitution: (12.833 / 27) × (1 + 0.1) = 0.4753 × 1.1 = 0.5228 yd³

Ready-mix suppliers always recommend adding 10% to account for uneven grade, ground settlement, and spillage.

Quick Answer

Calculate concrete volume for slabs (L × W × thickness in feet ÷ 27) and round piers. For a 10×10 ft slab at 4 inches thick, you need 1.23 cubic yards of concrete (approx 56 bags of 80 lb pre-mix, including a 10% spillage buffer).

Concrete Volume Calculator Formula & Sizing Rules

Yards = (Length ft × Width ft × (Thickness in / 12)) / 27
Mathematical Variable Legend for Concrete Volume Calculator Formula & Sizing Rules
VariableDefinitionStandard Units
YardsVolume of concrete to order in cubic yardsyd³
Waste%Recommended 10% safety margin for ground deflectionpercent

Ordering Ready-Mix Concrete vs Buying Pre-Mixed Bags

Ready-mix trucks deliver concrete in cubic yards (typically 1 to 10 yards per truck). For jobs under 1 cubic yard, buying pre-mixed 80 lb or 60 lb bags is usually more economical. One cubic yard requires 45 eighty-pound bags (0.60 ft³ yield each).

Common Project Sizing Mistakes

  • Not ordering a 10% buffer for uneven subgrade and forms bowing outward
  • Forgetting that 4 inches is 4/12 = 0.333 feet, not 0.4 feet

Frequently Asked Questions

How do you calculate cubic yards of concrete?▼
Multiply length (ft) × width (ft) × thickness (ft), then divide by 27. Add 10% for waste.
How many 80 lb bags of concrete make a cubic yard?▼
It takes 45 bags of 80 lb concrete to make one cubic yard (since each bag yields about 0.60 cubic feet, and 27 / 0.60 = 45).
How thick should a concrete slab or patio be?▼
Standard residential patios, walkways, and shed floors are poured 4 inches thick (0.333 ft). Driveways carrying cars or trucks typically require 5 to 6 inches with steel rebar or wire mesh reinforcement.
How many 60 lb bags of concrete make a cubic yard?▼
It takes 60 bags of 60 lb pre-mix concrete to make one cubic yard (each 60 lb bag yields approximately 0.45 cubic feet, and 27 / 0.45 = 60).

Authoritative Sources & Reference Standards

  1. Guide for the Use of the International System of Units (SI), NIST Special Publication 811 — National Institute of Standards and Technology (NIST). Verified 2026-10-01.

    Official SI unit definitions, conversion factors (Appendix B), and precision standards for cubic meters, liters, and US customary units.

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Reviewed by:VolumeCalculator.org Editorial Team·Last updated: 2026-10-01
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