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Concrete Calculator

Calculate concrete for any project

Units

Total Concrete Needed

1.36 yd³

Bags

62

Cost

$341

Weight

2.8 T

Add Rebar
Wire Mesh
10%
5%10% typical20%
$
Volume

1.36 yd³

Bags Needed

62

Weight

2.8 tons

Est. Cost

$341

Volume Breakdown

Raw Volume1.23 yd³
+ Waste0.12 yd³
Total Needed1.36 yd³
80 lb bag62 bags
Truck Loads (9 yd³)1

Cost Breakdown

Concrete$341
Total$341

Frequently Asked Questions

Q

How do I calculate how much concrete I need?

Volume = Length × Width × Thickness. Convert to cubic yards: Volume (cu ft) ÷ 27 = cubic yards. Example: 10ft × 10ft × 4in slab = 100 sq ft × 0.33 ft = 33 cu ft ÷ 27 = 1.22 cubic yards.

  • Formula: L × W × Thickness (in feet) = cubic feet
  • Convert to yards: Cubic feet ÷ 27 = cubic yards
  • 4 inch slab: Multiply sq ft × 0.33 ft ÷ 27
  • 6 inch slab: Multiply sq ft × 0.50 ft ÷ 27
  • Always round UP and add 5-10% waste
Slab ThicknessSq Ft per Cubic YardExample: 100 sq ft
4 inches81 sq ft1.23 cubic yards
5 inches65 sq ft1.54 cubic yards
6 inches54 sq ft1.85 cubic yards
8 inches40 sq ft2.47 cubic yards
Q

How many bags of concrete do I need?

One cubic yard = 45 bags (80 lb) or 60 bags (60 lb) or 90 bags (40 lb). For small projects: 80 lb bag covers 0.6 cu ft, 60 lb bag covers 0.45 cu ft. Bagged concrete is cost-effective under 1 cubic yard.

  • < 1 cubic yard: Bags are usually more practical
  • > 1 cubic yard: Ready-mix truck is more economical
  • 80 lb bags: Best value per cubic foot
  • Quikrete vs Sakrete: Similar performance, compare prices
Bag SizeYield (cu ft)Bags per Cu YardBest For
40 lb0.30 cu ft90 bagsSmall repairs
60 lb0.45 cu ft60 bagsPosts, small projects
80 lb0.60 cu ft45 bagsMost DIY projects
Q

How thick should my concrete slab be?

Driveway: 4-6 inches. Patio/sidewalk: 4 inches. Garage floor: 4-6 inches. Heavy equipment: 6-8 inches. Footings: Local code (often 8-12 inches). Thicker = stronger but more expensive. Rebar adds strength without extra thickness.

  • Add wire mesh or rebar for crack prevention
  • Thicker edges for driveways (6" apron)
  • Check local building codes for requirements
  • Proper base preparation is as important as thickness
ApplicationMinimum ThicknessRecommendedNotes
Sidewalk3.5"4"Light foot traffic
Patio4"4"Furniture, foot traffic
Driveway (cars)4"4-5"Regular vehicles
Driveway (trucks/RV)5"6"Heavy vehicles
Garage floor4"4-6"Depends on vehicles
Shed foundation4"4"Light structures
Q

Should I order extra concrete?

Yes! Order 5-10% extra for waste, spillage, and uneven subgrade. Better to have a little extra than to run short mid-pour. Ready-mix has minimums (often 1 yard). Leftover can be used for stepping stones or small projects.

  • 5% extra: Simple flat slabs with good forms
  • 10% extra: Uneven ground, complex shapes
  • 15% extra: Slopes, irregular edges
  • Running short mid-pour = disaster (cold joints)
  • Leftover concrete: Stepping stones, small repairs
Q

Ready-mix vs bagged concrete: Which is better?

Bagged: Best for < 1 cubic yard (< 45 bags). Ready-mix: More economical for 1+ cubic yards, faster, more consistent. Break-even is typically around 1 cubic yard. Factor in your time mixing bags.

  • Ready-mix minimum: Usually 1 yard (some do 0.5 yard)
  • Ready-mix: Order exact PSI strength you need
  • Saturday delivery: Often extra charge
  • Have helpers ready - concrete waits for no one!
FactorBagged ConcreteReady-Mix Truck
Best for< 1 cubic yard1+ cubic yards
Cost per yard$100-150$150-200 + delivery
LaborYou mix each bagTruck pours
QualityVariableConsistent
TimeHours of mixingPoured in minutes
Q

What PSI concrete do I need?

2500 PSI: Residential footings. 3000 PSI: Driveways, patios (most common). 4000 PSI: Commercial, heavy traffic. 5000+ PSI: Industrial. Standard bagged concrete is 3000-4000 PSI. Higher PSI = stronger but more expensive.

  • 3000 PSI is standard for most residential
  • Freeze-thaw areas: Consider 4000 PSI + air entrainment
  • Bagged concrete: Usually 3000-4000 PSI
  • PSI develops over 28 days (reaches 70% in 7 days)
PSI RatingUse CasesCost
2500 PSIFootings, foundationsLowest
3000 PSIDriveways, sidewalks, patiosStandard
3500 PSIDriveways with heavy vehiclesModerate
4000 PSICommercial, garage floorsHigher
5000+ PSIIndustrial, freeze-thaw areasHighest

Example Calculations

1Standard Patio Slab (10×10 ft)

Inputs

Length10 ft
Width10 ft
Thickness4 inches

Result

Concrete Needed1.23 cubic yards
80 lb Bags56 bags
With 10% Waste1.35 cubic yards

A 100 sq ft patio at 4" thick requires about 1.23 yards. Order 1.5 yards from ready-mix or 56 bags.

2Two-Car Driveway

Inputs

Length20 ft
Width18 ft
Thickness5 inches

Result

Concrete Needed5.56 cubic yards
With 10% Waste6.1 cubic yards
RecommendationOrder ready-mix

At 5" thick for vehicles, a 360 sq ft driveway needs ~6 yards. Ready-mix is the only practical option.

3Fence Post Holes (10 posts)

Inputs

Posts10
Hole Diameter10 inches
Hole Depth24 inches

Result

Concrete per Post0.58 cu ft
Total for 10 Posts5.8 cu ft
80 lb Bags Needed10 bags

For fence posts, use 1 bag (80 lb) per post hole. Bagged concrete is perfect for this application.

Formulas Used

Concrete Volume (Rectangular)

Volume = Length × Width × Thickness

Basic formula for slabs, patios, and driveways.

Where:

Length= Length in feet
Width= Width in feet
Thickness= Thickness in feet (divide inches by 12)

Cubic Feet to Cubic Yards

Cubic Yards = Cubic Feet ÷ 27

Convert volume to ordering units (1 cubic yard = 27 cubic feet).

Cylinder Volume (Posts/Footings)

Volume = π × radius² × depth

For round holes like fence posts and tube footings.

Concrete Calculator Guide

Accurate concrete estimation prevents costly over-ordering or running short mid-pour. Always calculate carefully and add 5-10% for waste.

For projects under 1 cubic yard, bagged concrete from a hardware store is practical. Larger projects benefit from ready-mix delivery for consistency and time savings.

Consider your subgrade preparation, reinforcement needs, and local climate when planning. Proper preparation is as important as the concrete itself for long-lasting results.

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Last Updated: Mar 9, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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