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Concrete Calculator

Calculate Cubic Yards, Bags and Slab Volume

Last Updated: July 18, 2026•by Ahmed

Calculate concrete cubic yards, cubic feet, and bag counts for slabs, footings, columns, and steps. Free concrete volume estimator with wastage allowance.

Concrete Calculator

Estimate cubic yards, cubic feet, 60 lb and 80 lb bag counts, and optional bulk cost for slabs, footings, columns, and steps.

Bagged cost estimates use planning defaults of $5.50 per 60 lb bag and $6.50 per 80 lb bag. Use local supplier prices for final ordering.

Results

Results include adjusted volume, bag counts for 60 lb and 80 lb bags, and bulk versus bagged cost benchmarks.

Volume (cubic yards)
1.63 yd³
Volume (cubic feet)
44.00 ft³
60 lb bags needed
98
80 lb bags needed
74

Cost comparison

Bulk delivery estimate
$244
60 lb bag estimate
$539
80 lb bag estimate
$481

Project snapshot

Area
120.00 ft²
Volume before wastage
1.48 yd³

What is a Concrete Calculator?

Whether you are pouring a massive residential driveway, setting foundation footings, or anchoring a single fence post, getting your concrete measurements exactly right is critical. Ordering too little means a disastrous cold joint in the middle of your pour; ordering too much is literally throwing money into the dirt.

A concrete calculator is the essential planning tool that takes the guesswork out of your project by precisely converting your slab, footing, column, or steps dimensions into cubic yards, cubic feet, and exact bag counts (40 lb, 60 lb, or 80 lb). From DIY backyard patios to professional construction subbases, accurate volume estimation requires understanding more than just length and width. You must account for subgrade variations, form bowing, and standard wastage allowances to guarantee a successful pour.

Guide Content

How to Use the Concrete Calculator - Cubic Yards, Bags & Slabs

1. Select the pour shape

Choose slab, footing, column, or steps so the calculator applies the correct volume formula for your project type.

2. Enter dimensions

Input length and width in feet and thickness or depth in inches. Even a half-inch change in thickness can shift your cubic yard total noticeably on larger pours.

3. Choose mix and bag size

Select the concrete mix type and bag weight (40 lb, 60 lb, or 80 lb) to see how many bags you need alongside the cubic yard total.

4. Add a wastage allowance

Add 5 to 10% for most pours. Use the adjusted total for ordering ready-mix or purchasing bagged concrete to avoid coming up short on pour day.

Guide Content

Key Formulas

Slab volume formula

Cubic Yards = Length(ft) × Width(ft) × Thickness(in) ÷ 12 ÷ 27

Converts slab dimensions into cubic yards, the standard unit for ordering ready-mix concrete from a batch plant.

Bag count formula

Bags = (Cubic Yards × 27) ÷ Yield per Bag(ft³)

Estimates the number of bags needed based on total cubic feet. An 80 lb bag typically yields about 0.60 ft³; a 60 lb bag about 0.45 ft³; a 40 lb bag about 0.30 ft³.

Column volume formula

Cubic Yards = π × (Diameter ÷ 2)² × Depth(ft) ÷ 27

Calculates the volume of a circular column or round post footing from diameter and depth.

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Key Factors

01
Consideration

Subbase preparation

A well-compacted and level subbase reduces the risk of cracking and settlement. Poor subbase preparation is a leading cause of slab failure.

02
Consideration

Reinforcement

Rebar and wire mesh add tensile strength to concrete slabs. Most driveways and structural applications benefit from some form of reinforcement.

03
Consideration

Mix design

Standard residential concrete uses a 4000 psi mix. High-traffic or freeze-thaw areas may need air-entrained mixes or higher strength ratings.

04
Consideration

Weather and curing

Hot or cold weather affects concrete curing. Protect fresh pours from direct sun, freezing temperatures, and rain to achieve full design strength.

Guide Content

Concrete Thickness Guide

Walkway or patio

4 inches

Standard thickness for foot-traffic-only surfaces. A well-prepared compacted base is important at this thickness.

Residential driveway

5–6 inches

Extra thickness handles passenger vehicle loads. Heavier trucks or delivery vehicles may warrant 6 inches with reinforcement.

Garage floor

4–6 inches

Most garage floors use 4 to 6 inches. Vehicle weight, number of vehicles, and soil conditions influence the final choice.

Foundation footing

Engineer specified

Structural footings depend on soil bearing capacity, building loads, and local codes. Use engineered drawings for final depths.

Guide Content

Typical Project Ranges

Small repair or post hole

Under 0.5 cubic yards

Bagged concrete is the most practical option. A few 80 lb bags are typically enough for post holes and small patches.

Patio or walkway

1–5 cubic yards

Depending on project size, this range can work with bagged mix or a small ready-mix order. Compare cost per cubic yard before deciding.

Driveway or larger slab

5+ cubic yards

Ready-mix delivery is usually more economical above this volume. Batch plant minimums vary but often start around 1 cubic yard.

Guide Content

Related Planning Tools

Cement Calculator

Calculate cement bags, sand, and aggregate quantities for concrete or mortar mixing by ratio.

Gravel Calculator

Estimate gravel cubic yards and tons for subbase, drainage, driveways, and landscaping projects.

Sand Calculator

Calculate sand volume, weight, and bags for paving, bedding, and concrete mix projects.

Guide Content

Frequently Asked Questions

How do I calculate how much concrete I need?
Measure length, width, and thickness in feet, then multiply all three together and divide by 27 to get cubic yards. This concrete calculator handles slabs, footings, columns, and steps automatically.
How many cubic yards of concrete do I need for a 10x10 slab?
A 10x10 foot slab at 4 inches thick needs approximately 1.23 cubic yards of concrete before wastage. Adding a 10% allowance brings that to about 1.35 cubic yards.
How many 80 lb bags of concrete do I need per cubic yard?
You need approximately 45 bags of 80 lb concrete mix to make one cubic yard. For 60 lb bags the number is around 60, and for 40 lb bags it is around 90.
What is the standard thickness for a concrete slab?
A typical residential slab is 4 inches thick for patios, walkways, and garage floors. Driveways often use 5 to 6 inches. Structural slabs may require engineered thickness based on load requirements.
Should I order ready-mix or use bags?
Bagged concrete is practical for pours under about 1 cubic yard. Ready-mix is more economical and practical for larger pours such as driveways, full patios, and foundation work.
What wastage factor should I use for concrete?
A 5 to 10% wastage allowance is typical for most residential pours. Irregular shapes, sloped sites, or pours with many penetrations may need a higher allowance.
How thick should a concrete driveway be?
Residential driveways commonly use 5 to 6 inches of concrete. Areas that will carry heavier vehicles may need 6 inches or more with appropriate reinforcement.
What is the difference between concrete and cement?
Cement is one ingredient in concrete. Concrete is a mixture of cement, sand, aggregate (gravel or crushed stone), and water. Cement is the binding agent that holds the mix together.
How long does concrete take to cure?
Concrete reaches about 70% of its design strength in 7 days and approximately 99% in 28 days under normal curing conditions. Foot traffic is usually safe after 24 to 48 hours.
Can I use this calculator for concrete footings?
Yes. Select the footing or rectangular shape, enter the footing width, length, and depth, and the calculator will return cubic yards, cubic feet, and bag counts for your footing pour.

Disclaimer

This calculator provides planning estimates only. Actual concrete quantities depend on site conditions, subbase variation, form accuracy, and supplier yield data. Confirm final volumes with your ready-mix supplier or contractor before ordering.