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Concrete Calculator

Slab / Wall

Calculate volume for slabs, square footings, walls, or any rectangular concrete structure.

% Recommended: 5–10%
💰 Optional Cost Estimation
📐 Interactive Diagram

Concrete Calculator Overview

A concrete calculator is an online construction tool that converts length, width, and depth measurements into concrete volume in cubic yards (yd³), cubic feet (ft³), and cubic meters (m³). This concrete volume calculator determines the number of pre-mixed concrete bags needed (in 40 lb, 50 lb, 60 lb, and 80 lb sizes), provides a material breakdown for custom mixes (cement, sand, gravel, and water), and estimates project cost in 60+ currencies. The Concrete Calculator supports 10+ structure types, including slabs, columns, round footings, circular slabs, tubes, curb and gutter barriers, stairs, post holes, and block fill.

This concrete calculator online tool serves 3 primary functions: volume calculation, bag estimation, and cost estimation. Enter dimensions in any combination of feet, inches, meters, centimeters, millimeters, or yards. The calculator handles all unit conversions internally and displays results in both imperial and metric units.

The concrete quantity calculator works for residential projects (patios, driveways, sidewalks), commercial construction (foundation footings, retaining walls), and small repairs (post holes, block fill). A built-in 0–50% safety buffer accounts for waste from spillage, uneven ground, over-excavation, and formwork absorption.

How to Calculate Concrete Volume — Formula of Calculation

To calculate concrete volume for a rectangular slab, multiply Length × Width × Depth in feet, then divide by 27 to convert to cubic yards. The formula is:

Volume (yd³) = (Length ft × Width ft × Depth ft) ÷ 27

For cylindrical structures like columns and round footings, the formula uses π (pi):

Volume (yd³) = π × (Diameter ft ÷ 2)² × Height ft ÷ 27

Enter your dimensions into the interactive formula visualizer below. The concrete calculator converts measurements to all 3 volume units — cubic yards, cubic feet, and cubic meters — and renders a 3D shape that updates as dimensions change.

0.00
Cubic Yards
0.00
Cubic Feet
0.0000
Cubic Meters

Why Use the Concrete Calculator?

This concrete calculator eliminates manual math errors, prevents over-ordering or under-ordering concrete, and saves time on material estimation. There are 5 reasons to use a concrete calculator before ordering:

  1. Accurate volume conversion — automatically converts between cubic yards, cubic feet, and cubic meters
  2. Bag count precision — calculates exact 40 lb, 50 lb, 60 lb, and 80 lb bag quantities
  3. Cost control — estimates total cost based on local concrete prices per cubic yard
  4. Waste reduction — adjustable safety buffer prevents cold joints from mid-pour shortages
  5. Multi-structure support — handles slabs, columns, footings, stairs, curbs, and post holes in one tool

Standard Thickness of Concrete

Standard thickness of concrete varies by project type. Select a project below to see the recommended minimum thickness in both inches and centimeters.

🚶
Sidewalk
4 in (10 cm)
Foot traffic only. Standard residential and commercial sidewalks.
🏡
Patio Slab
4 in (10 cm)
Outdoor living spaces. Use rebar for slabs over 10×10 ft.
🚗
Driveway
5–6 in (12–15 cm)
Standard vehicle traffic. 6 inches for heavy trucks or RVs.
🏗️
Garage Floor
6 in (15 cm)
Vehicle loads plus equipment. Reinforced with wire mesh or rebar.
🧱
Footing
8–12 in (20–30 cm)
Foundation support. Depth depends on soil type and frost line.
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Foundation Wall
8–10 in (20–25 cm)
Below-grade structural walls. Reinforced with vertical rebar.

Magic Number Method

The Magic Number method uses a single multiplier to convert square footage directly to cubic yards based on slab thickness. Multiply the area in square feet (ft²) by the Magic Number for your chosen thickness.

Thickness Magic Number Example (100 ft²)
4 inches 0.012346 100 × 0.012346 = 1.23 yd³
5 inches 0.015432 100 × 0.015432 = 1.54 yd³
6 inches 0.018519 100 × 0.018519 = 1.85 yd³
8 inches 0.024691 100 × 0.024691 = 2.47 yd³

The Magic Number equals thickness (in feet) ÷ 27. For a 4-inch slab: (4 ÷ 12) ÷ 27 = 0.012346. Multiply this by any square footage to get cubic yards without converting individual dimensions.

Example Calculation

Calculate concrete needed for a 20×20 ft driveway slab at 5 inches thick:

  1. Convert depth to feet: 5 inches ÷ 12 = 0.4167 ft
  2. Calculate volume in cubic feet: 20 × 20 × 0.4167 = 166.67 ft³
  3. Convert to cubic yards: 166.67 ÷ 27 = 6.17 yd³
  4. Convert to cubic meters: 166.67 × 0.0283168 = 4.72 m³
  5. Add 10% buffer: 6.17 × 1.10 = 6.79 yd³ (order 7 yards)
  6. Calculate 80 lb bags equivalent: 6.79 × 45 = 306 bags

This driveway project uses more than 1 cubic yard of concrete, making ready-mix concrete delivery from a ready-mix plant more practical than buying 306 individual 80 lb bags.

Concrete Project Types

Calculate concrete for slabs, patios, driveways and walls using length, width and thickness. Select a project type below to use the dedicated calculator.

🧱
Slabs, Patios & Driveways
The Slab / Wall calculator handles patios, driveways, garage floors, and footings using the rectangular volume formula (L × W × D).
See the full Slab Calculator guide →
🔵
Columns & Round Footings
The Sonotube / Column calculator handles cylindrical columns, piers, round footings, and post holes using the cylinder volume formula (π × r² × h).
See the full Sonotube Calculator guide →
🕳️
Post Holes
Calculate concrete for fence posts, mailbox posts and deck supports. Automatically subtracts the post volume from the hole.
Use Post Hole Calculator
🏛️
Foundation Footings
The Concrete Footings calculator handles strip, pad, and stepped footings for foundation support using length, width, and depth.
See the full Footings Calculator guide →
🪜
Stairs & Steps
Calculate concrete for entry stairs, porch steps and platforms using rise, run, width and number of steps.
Use Steps Calculator
🧱
Block Fill
Calculate concrete or grout to fill hollow CMU cinder block cores. Select 8, 10 or 12 inch block sizes.
Use Block Fill Calculator

Cost Estimation

Concrete cost depends on volume, delivery method (ready-mix vs. bags), location, and mix strength. For a full breakdown of material cost, delivery fees, labor, finishing, and a ready-mix-versus-bag comparison calculator, visit our Concrete Cost Estimator.

Specialized Concrete Calculators

Explore our suite of specialized concrete calculators designed for specific construction tasks, from slabs and footings to steps, bags, and cost estimation.

📏
4 Inch and 6 Inch Concrete Slab Calculator
Thickness Comparison
Use Calculator
📦
60 and 80 lb Concrete Bag Calculator
Sakrete & Quikrete Bag Count
Use Calculator
⚖️
20kg Concrete Bag Calculator
Metric Bag Sizing
Use Calculator
💰
Concrete Cost Estimator
Budget & Pricing Estimator
Use Calculator

Concrete Calculator FAQs

1 cubic yard (yd³) of concrete equals 27 cubic feet (ft³) or 0.7646 cubic meters (m³) and weighs approximately 3,900 lbs (1,769 kg). Ready-mix concrete from a ready-mix plant costs $125–$165 per cubic yard on average, with prices varying by region, delivery distance, and mix strength (measured in psi or MPa).
One 80 lb bag of concrete covers 0.6 cubic feet (ft³). Divide the total cubic feet needed by 0.6 to get the bag count. For larger projects over 1 cubic yard, ordering ready-mix concrete from a ready-mix company is more cost-effective.
A 50-pound bag of concrete yields approximately 0.375 cubic feet (ft³) of mixed concrete, which equals 0.0106 cubic meters (m³). A standard 60 lb bag yields 0.45 ft³, and an 80 lb bag yields 0.6 ft³. Use this concrete bag calculator to determine the exact number of bags needed for any project.
Order ready-mix concrete for projects larger than 1 cubic yard (27 cubic feet). Pre-mixed concrete bags work best for small repairs, post holes, and projects under 0.5 yd³. A ready-mix company delivers concrete mixed to specification, saves labor time, and costs less per cubic yard for larger volumes. Bags give more control for small, precise pours.
An online concrete calculator provides instant volume, cost, and material estimates with visual diagrams, while a physical construction calculator requires manual formula entry. Online tools handle unit conversions between feet, inches, meters, and yards automatically. Both use the same geometric formulas. This concrete volume calculator supports 10+ structure types and 60+ currencies for cost estimation.
Concrete weighs approximately 150 pounds per cubic foot (2,400 kg per cubic meter). One cubic yard of concrete weighs about 3,900 lbs (1,769 kg). Lightweight concrete weighs 90–120 lbs/ft³ (1,440–1,920 kg/m³). Reinforced concrete with rebar weighs 5–10% more than plain concrete.
Concrete was invented around 3000 BC by Nabataean traders in regions of southern Syria and northern Jordan. The Romans advanced concrete technology around 300 BC using volcanic ash (pozzolana) mixed with lime. Roman concrete structures like the Pantheon (built 125 AD) still stand today. Modern Portland cement was patented in 1824 by Joseph Aspdin in England.
Concrete takes 24–48 hours to set enough for foot traffic and 28 days to reach full strength (curing). At 7 days, concrete reaches about 70% of its rated strength. Temperature, humidity, and mix design affect curing time. Keep concrete moist during the first 7 days for optimal strength. Cold weather slows curing, and hot weather accelerates surface drying.
One cubic yard requires approximately 45 bags of 80 lb concrete, 60 bags of 60 lb, 72 bags of 50 lb, or 90 bags of 40 lb. For example, each 80 lb bag yields 0.6 cubic feet of mixed concrete, and one cubic yard equals 27 cubic feet: 27 ÷ 0.6 = 45 bags. Use pre-mixed concrete bags for small projects (under 1 yard) and ready-mix delivery for larger volumes.