SamCalculator

Concrete Calculator

Calculate concrete volume, weight, material requirements, truck loads, and estimated costs for slabs, footings, foundations, columns, stairs, walls, curbs, gutters, and other construction projects.

Concrete Slab, Wall & Square Footing Calculator

Calculate concrete volume for rectangular slabs, walls, pads, and square footings. Enter length, width, thickness and get precise volume, weight, bag counts, and truck loads.

Dimensions

LWH

Interactive diagram — scales with inputs

in your currency
total
total

Cement

0 kg

0 × 50 kg bags

Sand

0 kg

Aggregate

0 kg

Water

0 L

Based on 0.00 m³ (with 5% waste) at 1:1.5:3 ratio.

Calculate concrete volume first to see mix quantities.

Standard Thickness Reference

ApplicationRec. ThicknessMix Grade
Residential Patio4"M15–M20
Driveway5–6"M20–M25
Garage Floor5"M20
Sidewalk / Path4"M15
Foundation (Spread)10–12"M20–M25
Retaining Wall12"M20–M25
Structural Column12–18"M25–M30
Stairs6″ riserM20

Curing Time Guide

2–4 h

Initial Set

7 days

70% Strength

28 days

Full Cure

Keep concrete moist for ≥ 7 days. Avoid loading until 28-day cure is complete.

What Is Concrete Volume?

Concrete is the backbone of modern construction — from driveways and patios to foundations, columns, and stairways. Getting the volume right before you order means no wasted mix, no expensive short pours, and no second trips to the supplier.

This calculator handles five distinct concrete shapes — rectangular slabs, cylindrical columns, hollow tubes, curb-and-gutter sections, and concrete stairs — each with its own geometry, formula, and industry-standard reference. Enter your dimensions, select a mix type, set a waste allowance, and get precise results in seconds.

How Concrete Is Measured

1

Choose Your Structure

Select a tab — slab, column, tube, curb, or stairs — to match the concrete element you are building.

2

Enter Dimensions

Type in length, width, diameter, height, or riser count. All inputs support mm, cm, m, inches, feet, and yards.

3

Pick Concrete Type & Waste

Choose standard, reinforced, lightweight, or high-strength concrete and set a 0–15% waste allowance.

4

Calculate & Export

Tap Calculate to see volume, weight, bags, truck loads, cost estimates, and mix design — then copy, share, or print.

6 Ways to Use This Calculator

01

Residential Slab Planning

Enter your garage, patio, or basement slab dimensions to get cubic yards and the exact number of 80-lb bags or ready-mix trucks you need.

02

Foundation Footings

Use the slab tab with thickness set to your footing depth. Multiply by quantity for multiple footings under a house or deck.

03

Column & Post Installation

The cylindrical tab calculates concrete for fence post holes, deck piers, and structural columns from diameter and depth alone.

04

Road & Kerb Works

The curb and gutter tab uses a real cross-section formula — curb depth × curb height plus gutter width × flag thickness — for civil engineering accuracy.

05

Stair Construction

Enter rise, run, width, and riser count to estimate the full concrete volume for a stairway, including the landing platform.

06

Mix Design Verification

Enable the Mix Design Estimator to see exactly how many kilograms of cement, sand, aggregate, and water a given grade of concrete requires per cubic metre.

Concrete Estimation Best Practices

Always Add a Waste Factor

Industry standard is 5–10% for most residential work and up to 15% for complex shapes like stairs or uneven sub-base conditions. Never order exactly.

Order in Cubic Yards, Not Bags

Once your project exceeds about 1 cubic yard (around 60 × 80-lb bags), ready-mix concrete is faster to place, cheaper per unit, and more consistent in quality.

Verify Sub-Base Depth

A 4-inch slab on a 6-inch compacted gravel base performs far better than a 6-inch slab on unprepared soil. Measure actual depth before calculating.

Check Temperature Before Pouring

Concrete should not be placed when ambient temperatures are below 4°C (40°F) or above 35°C (95°F). Use the curing time estimator in Advanced Mode.

Why Accurate Concrete Estimation Matters

Over-ordering concrete wastes money and creates disposal problems — a single extra cubic yard can cost $150–$300 in ready-mix alone. Under-ordering on a critical pour means joints, cold seams, and structural weak points that can cost thousands to repair.

Professional estimators cross-check their calculations using multiple methods. This tool gives you the same formulas used by concrete suppliers, ready-mix schedulers, and civil engineering textbooks — so your numbers match what shows up on the invoice.

Core Concrete Volume Formulas

Rectangular Slab

V = L × W × H

Length × Width × Thickness. Multiply by quantity for multiple identical slabs.

Cylindrical Column

V = π × (D/2)² × H

Pi times radius squared times height. D is outer diameter.

Hollow Tube / Ring

V = π × ((D₁/2)² − (D₂/2)²) × H

Outer radius squared minus inner radius squared, times π times height.

Curb & Gutter

V = (Curb_D × Curb_H + Gutter_W × Flag_T) × L

Cross-section area (curb portion + gutter portion) times total run length.

Concrete Stairs

V = W × N × Rise × (N × Run / 2 + Platform_D)

Width times number of risers times rise height times stair body plus platform depth.

Concrete Mix Ratios Explained

GradeRatio (C:S:A)Strength (MPa)Best For
M51:5:105 MPaLean concrete, fillings
M7.51:4:87.5 MPaPCC, blinding concrete
M101:3:610 MPaGeneral construction
M151:2:415 MPaSlabs, beams, footings
M201:1.5:320 MPaRCC slabs, beams, columns
M251:1:225 MPaHeavy-duty structures
M30Custom30 MPaHigh-strength structures

Common Concrete Calculation Mistakes

Forgetting quantity multiplier

Multiple footings or columns? Use the Quantity field — don't multiply after the fact.

Mixing units mid-calculation

Each dimension has its own unit selector. Keep all dimensions in the same unit or let the calculator convert automatically.

No waste allowance for irregular shapes

Curbs, gutters, and stairs have more waste than flat slabs. Use 10–15% for complex pour shapes.

Ordering too many small trucks

One 8-yard truck is cheaper per yard than two 4-yard trucks. Combine small adjacent pours.

Ready-Mix vs Bagged Concrete

Ready-Mix Concrete

  • Best for projects > 1 cubic yard
  • Consistent quality from certified plant
  • Faster to place — pour entire slab at once
  • Available in custom mix designs
  • Minimum order and delivery fees apply

Bagged Concrete

  • Best for projects < 1 cubic yard
  • No minimum order — buy exactly what you need
  • Mix at your own pace
  • Higher cost per unit than ready-mix
  • Available at hardware stores nationwide

How We Calculated This

All formulas in this calculator are derived from geometric first principles and cross-referenced against the ACI 318 Standard for Structural Concrete, the Portland Cement Association (PCA) design guide, and the Ready Mixed Concrete Association (RMCA) best-practice guidelines.

Bag yield figures are based on published data from Quikrete and Sakrete product specifications. Ready-mix truck capacity uses the U.S. industry-standard 8 cubic yard drum load. All calculations are performed client-side — no data is sent to a server.

Concrete Calculator FAQ

Multiply the length × width × thickness (in the same units) to get volume, then convert to cubic yards by dividing by 27 (if working in feet). For example, a 10 ft × 10 ft × 4 in slab = 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards.

One 80-lb bag of Quikrete or Sakrete yields approximately 0.60 cubic feet. One cubic yard = 27 cubic feet, so you need roughly 45 × 80-lb bags per cubic yard. Always add 5–10% extra.

A 40 kg bag yields approximately 0.017 m³. One cubic metre therefore requires approximately 59 × 40 kg bags. A 50 kg bag (0.0213 m³) requires about 47 bags per cubic metre.

Standard concrete weighs approximately 2,400 kg per cubic metre (150 lb/ft³ or 4,050 lb/yd³). Reinforced concrete is around 2,500 kg/m³, lightweight concrete around 1,800 kg/m³.

Use 5% for simple flat slabs with straight edges. Use 10% for walls, columns, and typical residential work. Use 15% for complex shapes like stairs, curbs, and uneven subgrades. Never order exactly — a short pour mid-job creates structural cold joints.

There are exactly 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft). To convert cubic feet to cubic yards, divide by 27. To convert cubic yards to cubic metres, multiply by 0.7646.

Ready-mix concrete is produced in a central batching plant and delivered by transit mixer trucks. It is the best choice when your project exceeds about 1 cubic yard (0.76 m³). Below that threshold, pre-mixed bags are usually more cost-effective and convenient.

A standard drum-mixer truck in the US carries 8 cubic yards (approximately 6.12 m³). Divide your required volume (with waste) by 6.12 to find the number of full trucks. Always round up — partial loads are billed at minimum charge rates.

For residential driveways, M20 (1:1.5:3 mix ratio, approximately 4,000 PSI) is the most widely recommended grade. Use M25 for heavy vehicle loads such as RVs or commercial vehicles. Minimum thickness is 4 inches; 5–6 inches is preferred.

Volume = π × (Diameter ÷ 2)² × Height. For a 12-inch diameter, 3-foot deep post hole: π × (0.5 ft)² × 3 = 2.36 ft³ = 0.087 yd³ = approximately 4 × 80-lb bags per hole.

The number indicates the characteristic compressive strength in MPa at 28 days. M15 ≈ 2,175 PSI (light slabs), M20 ≈ 2,900 PSI (standard structural), M25 ≈ 3,625 PSI (heavy structures). Higher grades use more cement and less water-to-cement ratio.

Use the Stairs tab in this calculator. The formula is V = Width × N × Rise × (N × Run ÷ 2 + Platform Depth). For example, 6 risers at 7-inch rise, 11-inch run, 36-inch width, and a 12-inch platform: V ≈ 9.24 cubic feet or 0.34 cubic yards.

Standard plain concrete: 2,300–2,400 kg/m³ (143–150 lb/ft³). Reinforced concrete (with rebar): 2,400–2,500 kg/m³. Lightweight concrete (expanded clay or foam): 1,400–1,900 kg/m³. High-strength concrete: 2,450–2,600 kg/m³.

Concrete reaches approximately 70% of its design strength in 7 days and 99% in 28 days under standard conditions (20°C / 68°F). At 10°C it may take 50% longer. At 30°C it hydrates faster but final strength is slightly lower. Keep concrete moist for at least 7 days after placement.

Concrete should not be placed when the ambient temperature is below 4°C (40°F) or when freezing is expected within 24 hours. Use hot water in the mix, insulated forms, and heated enclosures if you must pour in cold weather. Freeze–thaw damage is the leading cause of premature concrete failure.

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