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Concrete Calculator

Calculate concrete in cubic yards and pre-mixed bags (80-lb & 60-lb) for slabs, post footings, and trenches with visual dimension guides.

Slab Geometry & Layers10′ × 10′ @ 4″ thick
Length (L)Width (W)Depth (T)
ft
ft
4″ = standard 2×4 form
in
Gravel Base & Rebar Takeoff (Optional)▼

Enter dimensions to calculate

Instantly compute ready-mix cubic yards, standard 80-lb and 60-lb pre-mixed bags, and hauling weight.

Quick Example:10 × 10 ft patio at 4″ thick → 1.36 cu yds = 61 80-lb bags.
Field Engineering & Pouring Guide

Concrete Estimating, Subgrade Prep & Pouring Workflow

Follow these industry-standard structural guidelines and visual cross-sections to prepare a crack-resistant subgrade, determine accurate yardage, place reinforcement, and cure high-strength concrete.

01

Measure True Dimensions

Measure length, width, and uniform depth in feet. For slabs, convert inches to feet (e.g. 4″ ÷ 12 = 0.333 ft). Calculate cubic feet and divide by 27 for cubic yards.

02

Apply +10% Safety Buffer

Always order 10% extra (15% for rough post holes) to compensate for subgrade grade variations, form board deflection, screed loss, and wheelbarrow spillage.

03

Compact Gravel & Rebar

Install 4″ of compacted #57 crushed stone or road base. Elevate #4 rebar or welded wire mesh onto chairs in the center of the slab height—never on bare dirt.

04

Pour, Joint & Moist Cure

Screed, bull-float, and edge within 45 minutes. Cut control joints at 2× slab thickness in feet (every 8–10 ft for a 4″ slab). Keep wet for 7 days for peak PSI.

Visual: Structural Slab Cross-Section

ACI Recommended

A durable outdoor slab requires a compacted gravel base, vapor barrier, centered rebar reinforcement on chairs, and grooved control joints.

4″ Concrete Slab (3,500 – 4,000 PSI)Control Joint (1″ depth)4″ Compacted Crushed Stone (#57 / Road Base)Undisturbed / Compacted Native Soil Subgrade

Visual: Sonotube Post Footing Elevation

Frost Depth

Deck footings and fence posts must extend below the local frost line (typically 36″–48″ in northern zones) with flared bases or bell footings.

Finished Grade12″ Sonotube36″–48″ DepthFlared Bell Footing PadFrost Depth Line

Recommended Slab Thickness & Compressive Strength (PSI)

Select the proper concrete mix strength (PSI) and thickness based on your load requirements and local climate.

ApplicationMin ThicknessDesign StrengthReinforcementControl Joint Spacing
Sidewalks & Walkways3.5″ (2×4 forms)3,000 – 3,500 PSIFiber mesh or WWFEvery 4 to 6 ft
Patios & Garden Sheds4.0″3,500 – 4,000 PSI#4 Rebar @ 18″ OC or WWFEvery 8 to 10 ft
Residential Driveways5.0″ – 6.0″4,000 – 4,500 PSI#4 Rebar @ 12″–18″ OCEvery 10 to 12 ft
Hot Tub & Heavy Equipment Pads6.0″4,000 – 4,500 PSI#4 Rebar @ 12″ OC gridEvery 10 to 12 ft
Post Footings & Sonotubes36″–48″ (depth)3,500 – 4,000 PSI2× #4 Vertical Rebar barsN/A (Isolated Column)

Ready-Mix Delivery Truck vs. Pre-Mixed Bags Decision Guide

Determine whether ordering a ready-mix truck or buying bagged concrete at the home center is right for your project.

Pre-Mixed Concrete Bags (DIY)

Under 1.5 Cu Yds (< 65 bags)
  • ✓Work at Your Own Pace: Mix 1–2 bags at a time in a wheelbarrow without the intense time pressure of a ready-mix truck.
  • ✓Zero Short-Load Fees: No delivery charges or minimum yardage penalties. Buy exact quantities and return unopened bags.
  • ⚠Physical Labor: 1 cubic yard requires lifting and mixing 45 separate 80-lb bags (3,600 lbs of material).

Ready-Mix Transit Truck Delivery

Over 1.5 Cu Yds (> 65 bags)
  • ✓Speed & Efficiency: Discharges 2 to 10+ cubic yards in 15–20 minutes, eliminating backbreaking manual mixing.
  • ✓Uniform Slump & Strength: Scientifically batched for consistent water-cement ratio, air entrainment, and 4,000 PSI strength.
  • ⚠Strict Pour Clock: Requires a crew of 2–4 workers with screeds, bull floats, and wheelbarrows ready before the truck arrives.
Concrete Calculation Engineering

How to Calculate Concrete Volume: Formulas, Bags & Ready-Mix Ordering

Whether you are using our concrete slab calculator for a 4-inch patio, a footing concrete calculator for Sonotubes, or estimating total yardage with our ready mix concrete calculator, precision planning prevents costly cold joints and material shortages.

1. Volume of Concrete Calculator: Slabs, Yards & Square Feet Formulas

Concrete is ordered in Cubic Yards (yd³ or cu yds) or mixed in pre-mixed bags (80-lb, 60-lb, 50-lb). Our concrete calculator square feet and concrete calculator in yards engine applies this standard geometric formula:

Concrete Calculator for Slab Formula

Volume (cu ft) = Length (ft) × Width (ft) × [Thickness (inches) ÷ 12]

Cubic Yards (cu yds) = Volume (cu ft) ÷ 27

With 10% Safety Buffer = Cubic Yards × 1.10

For piers, posts, and Sonotubes, our footing of concrete calculator applies cylinder geometry:

Footing Concrete Calculator Cylinder Formula

Radius (ft) = (Diameter in inches ÷ 2) ÷ 12

Volume per Hole (cu ft) = π (3.14159) × [Radius (ft)]² × Depth (ft)

Total Cubic Yards = [Volume per Hole × Quantity] ÷ 27

2. Concrete Bag Calculator: 80-lb & 60-lb Bag Yields

When using our concrete bag calculator and concrete calculator bags tool, each dry premix bag size yields an exact volume of wet mixed concrete:

  • 80-Pound Bag (0.60 cu ft): Exactly 45 bags per cubic yard (plan for 50 bags with 10% safety buffer).
  • 60-Pound Bag (0.45 cu ft): Exactly 60 bags per cubic yard (plan for 66 bags with 10% safety buffer).
  • 50-Pound Bag (0.375 cu ft): Exactly 72 bags per cubic yard (plan for 79 bags with 10% safety buffer).

3. Ready Mix Concrete Calculator, Price & Cost Estimating

Our concrete calculator cost and concrete calculator price tool helps homeowners evaluate the financial and physical trade-offs between readymix concrete calculator delivery and bagged premix:

Ready-Mix Delivery (Over 1.5 yds)

Ready-mix costs $125 to $180 per cubic yard. It discharges in 15–20 minutes with monolithic 4,000 PSI strength.

Bagged Concrete (Under 1.5 yds)

80-lb bags cost $5.50 to $7.50 per bag. Ideal for DIY post holes, small sidewalks, and patio patches without short-load delivery fees.

4. Sub-base Preparation, Rebar Grids & 28-Day Curing Rules

Pouring a crack-resistant slab requires:

  • ✓Compacted Gravel Base: 4 inches of #57 stone to prevent settlement and frost heaves.
  • ✓Elevated Rebar: #4 rebar on chairs positioned in the center of the slab height for tensile strength.
  • ✓Control Joints: Cut grooved joints at 2× slab thickness in feet (every 8–10 ft for a 4″ slab).
  • ✓7-Day Moist Curing: Keep damp with wet burlap or plastic sheeting to achieve 70%+ strength before full 28-day cure.
Frequently Asked Questions

Concrete Sizing, Bag Yields & Pouring FAQs

Expert answers to common homeowner and contractor questions regarding calculating cubic yards, bag counts per yard, slab thickness, rebar grid spacing, sub-base gravel, and ready-mix delivery.

General Concrete Estimating & Formulas

How much concrete do I need?
To determine how much concrete you need, calculate the volume of your project in cubic feet (Length in feet × Width in feet × Thickness in feet) and divide by 27 to convert into cubic yards. Always add a 10% safety buffer for slabs and formwork deflection (or 15% for rough-excavated post holes). For example, a 10 × 10 ft patio at 4 inches thick requires 1.23 cubic yards net, or 1.36 cubic yards with a 10% safety buffer (equivalent to 61 80-lb pre-mixed bags).
How do I calculate how much concrete I need?
Follow these 4 simple steps: 1. Measure Dimensions: Measure length and width in feet, and thickness in inches. 2. Convert Thickness to Feet: Divide thickness in inches by 12 (e.g. 4″ ÷ 12 = 0.333 ft). 3. Calculate Cubic Feet: Multiply Length (ft) × Width (ft) × Thickness (ft). 4. Convert to Cubic Yards: Divide total cubic feet by 27. Formula: (Length × Width × Thickness in inches ÷ 12) ÷ 27 × 1.10 (safety buffer) = Total Cubic Yards to order.
How many cubic yards of concrete do I need?
Cubic yardage depends on your project's square footage and thickness: • 100 sq ft @ 4″ thick (e.g. 10×10 patio): 1.36 cu yds (with 10% buffer) • 200 sq ft @ 4″ thick (e.g. 10×20 patio): 2.72 cu yds • 400 sq ft @ 4″ thick (e.g. 20×20 2-car garage pad): 5.43 cu yds • 600 sq ft @ 5″ thick (e.g. standard 2-car driveway): 10.19 cu yds Use our free concrete calculator to enter your exact dimensions and receive instant cubic yard and cubic meter totals.
How do I convert cubic feet of concrete to cubic yards?
To convert cubic feet (cu ft) to cubic yards (cu yds), divide total cubic feet by 27, because 1 cubic yard = 27 cubic feet (3 ft × 3 ft × 3 ft = 27 ft³). Example: 54 cubic feet ÷ 27 = exactly 2.0 cubic yards.
How much extra concrete should I order?
Always order 10% extra concrete for standard slabs, walkways, and patios with rigid wood forms. For rough-excavated post holes, uneven subgrades, or deep footings, order 15% extra. Ordering an extra buffer prevents running short during a pour, which can create a weak structural 'cold joint' where fresh concrete meets hardened concrete.
how much concrete calculator
Our free 'how much concrete calculator' provides instant yardage, bag counts (80-lb, 60-lb, 50-lb), gravel sub-base, and rebar takeoffs for slabs, post holes, Sonotubes, and continuous foundation trenches. Simply select your project shape, input length, width, and thickness, and get instant material quantities.
how much concrete do i need calculator
The 'how much concrete do I need calculator' by YesMeasure accurately calculates ready-mix transit delivery volume, bag counts for standard 50-lb, 60-lb, and 80-lb pre-mixed bags, total wet hauling weight in tons, and delivery method recommendations (DIY bags vs ready-mix truck delivery).

Pre-Mixed Bags & Yields

How many bags of concrete do I need?
To calculate how many bags of concrete you need, multiply your total cubic feet of project volume by the bag rate: • For 80-lb bags: Divide total cubic feet by 0.60 cu ft (yields 45 bags per cu yd). • For 60-lb bags: Divide total cubic feet by 0.45 cu ft (yields 60 bags per cu yd). • For 50-lb bags: Divide total cubic feet by 0.375 cu ft (yields 72 bags per cu yd). Always round up to the nearest whole bag and purchase 10% extra for spillage.
How many bags of concrete are in a cubic yard?
There are: • 45 bags of 80-lb concrete in one cubic yard (plan for 50 bags with 10% buffer). • 60 bags of 60-lb concrete in one cubic yard (plan for 66 bags with 10% buffer). • 72 bags of 50-lb concrete in one cubic yard (plan for 79 bags with 10% buffer). • 90 bags of 40-lb fast-setting concrete in one cubic yard (plan for 99 bags with 10% buffer).
How much concrete does one cubic yard cover?
One cubic yard (27 cubic feet) of concrete covers: • At 2 inches thick: 162 square feet • At 3 inches thick: 108 square feet • At 3.5 inches thick (2×4 form): 92.6 square feet • At 4 inches thick (Standard Patio): 81 square feet • At 5 inches thick (Driveway): 64.8 square feet • At 6 inches thick (Heavy Duty Pad): 54 square feet

Slabs, Patios, Walkways & Driveways

How do I calculate concrete for a slab?
To calculate concrete for a rectangular slab: 1. Multiply Length (ft) × Width (ft) = Square Footage Area. 2. Multiply Area (sq ft) × [Thickness (inches) ÷ 12] = Total Cubic Feet. 3. Divide Cubic Feet by 27 = Cubic Yards. 4. Multiply Cubic Yards by 1.10 for a 10% safety buffer. Example: A 12 × 16 ft patio at 4 inches thick: 12 × 16 × (4 ÷ 12) = 64 cu ft ÷ 27 = 2.37 cu yds. Adding 10% = 2.61 cubic yards (or 118 80-lb bags).
How much concrete do I need for a 10×10 slab?
A 10 ft × 10 ft slab (100 square feet): • At 4 inches thick: 1.23 cu yds net (1.36 cu yds with 10% buffer) = 61 80-lb bags or 82 60-lb bags. • At 5 inches thick: 1.54 cu yds net (1.70 cu yds with 10% buffer) = 77 80-lb bags or 102 60-lb bags. • At 6 inches thick: 1.85 cu yds net (2.04 cu yds with 10% buffer) = 92 80-lb bags or 123 60-lb bags.
How much concrete do I need for a 4-inch slab?
A 4-inch thick slab requires 0.01235 cubic yards per square foot (or 1 cubic yard per 81 square feet). Multiply your total square footage by 0.01235 and add 10%. Quick 4-Inch Slab Yardage Guide: • 50 sq ft: 0.68 cu yds (31 80-lb bags) • 100 sq ft: 1.36 cu yds (61 80-lb bags) • 150 sq ft: 2.04 cu yds (92 80-lb bags) • 200 sq ft: 2.72 cu yds (123 80-lb bags) • 400 sq ft: 5.43 cu yds (245 80-lb bags)
How do I calculate concrete for a circular slab?
For a circular patio or round pad, use the cylinder volume formula: 1. Radius = Diameter in feet ÷ 2 2. Area (sq ft) = π × Radius² (3.14159 × Radius × Radius) 3. Volume (cu ft) = Area × (Thickness in inches ÷ 12) 4. Cubic Yards = Volume (cu ft) ÷ 27 × 1.10 Example: A 12 ft diameter circular fire pit patio at 4″ thick: Radius = 6 ft. Area = 3.14159 × 36 = 113.1 sq ft. Volume = 113.1 × (4 ÷ 12) = 37.7 cu ft ÷ 27 = 1.40 cu yds net (1.54 cu yds with 10% buffer = 70 80-lb bags).
How do I calculate concrete for a sidewalk?
Sidewalks and walkways are typically 3.5 inches thick (using standard 2×4 lumber forms) and 3 to 4 feet wide: • Formula: Length (ft) × Width (ft) × (3.5 ÷ 12) ÷ 27 × 1.10 = Cubic Yards. • Example: A 4 ft wide × 50 ft long sidewalk at 3.5 inches thick: 50 × 4 × (3.5 ÷ 12) = 58.33 cu ft ÷ 27 = 2.16 cu yds net (2.38 cu yds with 10% buffer = 107 80-lb bags).
How do I calculate concrete for a driveway?
Residential driveways should be poured at 5 inches thick (or 6 inches for heavy pickup trucks and RVs) with #4 rebar on an 18″ grid: • Formula: Length (ft) × Width (ft) × (5 ÷ 12) ÷ 27 × 1.10 = Cubic Yards. • Single-Car Driveway (12 ft × 40 ft = 480 sq ft) at 5″ thick: 480 × (5 ÷ 12) ÷ 27 = 7.41 cu yds net (8.15 cu yds with 10% buffer → order an 8.5 yard ready-mix truck). • Two-Car Driveway (20 ft × 40 ft = 800 sq ft) at 5″ thick: 800 × (5 ÷ 12) ÷ 27 = 12.35 cu yds net (13.58 cu yds with 10% buffer → order 14 cubic yards).

Footings, Sonotubes & Post Holes

How do I calculate concrete for footings?
• Continuous Trench Footings: Length (ft) × [Width (inches) ÷ 12] × [Depth (inches) ÷ 12] ÷ 27 × 1.10 = Cubic Yards. Example: A 60 ft long × 16″ wide × 12″ deep trench footing = 60 × 1.333 × 1.0 = 80 cu ft ÷ 27 = 2.96 cu yds (3.26 cu yds with 10% buffer). • Round Post Holes & Sonotubes: (Diameter in inches ÷ 24)² × 3.14159 × Depth in feet ÷ 27 × Quantity × 1.15 = Total Cubic Yards. Example: 6 deck post holes (12″ diameter × 3 ft deep) = 0.087 cu yds per hole × 6 = 0.52 cu yds (0.60 cu yds with 15% buffer = 27 80-lb bags).