How do I calculate yards of concrete?

Multiply length × width × thickness (all in feet) to get cubic feet, then divide by 27 to get cubic yards. For example, a 10 ft × 10 ft slab at 4 inches thick = 33.3 ft³ ÷ 27 = 1.23 yd³. This calculator does the conversion automatically for any shape and unit.

How do you calculate concrete yardage for a slab?

Convert all dimensions to feet first (e.g., 4 inches = 0.333 ft). Then multiply length × width × thickness to get cubic feet. Divide by 27 to get cubic yards. The calculator handles the conversion when you use inch or cm inputs.

How many 80 lb bags of concrete are in a yard?

One 80 lb bag yields about 0.6 cubic feet. Since 1 cubic yard = 27 cubic feet, you need 27 ÷ 0.6 = 45 bags of 80 lb concrete to make 1 yard. A 60 lb bag yields about 0.45 ft³, so you’d need about 60 bags per yard. The calculator computes bag count automatically for any bag size.

How much area does one cubic yard of concrete cover?

At 4 inches thick, 1 cubic yard covers about 81 square feet. At 6 inches, it covers about 54 square feet. Use the formula: coverage (ft²) = 324 ÷ thickness (inches). The calculator lets you enter any slab dimensions and shows the exact volume needed.

Can I use this as a concrete pad calculator?

Yes. Select the Slab / Pad shape, enter your length and width, set the thickness (typically 4 inches for patios or 5–6 inches for driveways), and the calculator gives you volume in yards, cubic feet, and cubic meters. Add a bag size to see how many bags of concrete you need.

Can I use this as a concrete cost calculator?

Yes. Toggle “Bag & cost estimate” on, then add your local ready-mix price per yard/m³ and bag price per bag. The calculator compares ready-mix vs bagged cost and shows the cheaper option.

How many bags of concrete do I need?

Bag count equals total volume divided by the yield per bag, rounded up to the next whole bag. Enter bag size and price in the bag & cost estimate panel to see the exact count.

Should I order extra concrete for waste?

Yes. A 5-10% buffer is common to cover spillage, form loss, and uneven subgrades. The calculator defaults to 10% waste and you can adjust the slider to match your project.

What thickness should a concrete slab be?

Many patios use 4 inches, while driveways and heavy loads often use 5–6 inches. Follow local code for your project. Enter the thickness in inches or centimeters and the calculator handles the conversion.

How do I estimate concrete for footings or walls?

Use the rectangular formula (length × width/height × thickness) and include any waste allowance. Switch the shape dropdown to Footing or Wall and enter your dimensions.

Ready-mix vs bagged concrete: which is cheaper?

For larger pours (over 1 yd³), ready-mix at a typical $130–$160 per yard is usually cheaper than bags at $5–$8 each. Bagged mix works well for small patch jobs under 0.5 yd³. Typical market range as of June 2026. Check local suppliers for current pricing — actual costs vary by region, order size, and delivery distance.

Concrete Calculator

Name: Concrete Calculator
Author: Ganak

Flat rectangular slab: length × width × thickness.

Units

Length (ft)

Width (ft)

Thickness (ft)

Quantity

Waste / overage

Waste percentage

Add extra for cuts and waste

Bag & cost estimate

Bag count, cost, and weight. Override yield if needed.

Slab / Pad

Includes 10% waste · Qty 1

Total volume

1.36yd3

1.36 yd³36.7 ft³1.04 m³

Order & cost summary

Volume, bags, weight & cost at a glance

Suggested order

1.5 yd3

Rounded for delivery

Estimated weight

5,500 lb(2,495 kg)

What is a Concrete Calculator?

Overview of the tool and what it helps you estimate

A concrete calculator (also called a concrete volume or yardage calculator) estimates how much concrete you need for slabs, pads, footings, walls, columns, stairs, and curbs. It converts volume into cubic yards, cubic feet, and cubic meters, so you can order ready-mix or plan bag counts with confidence. Whether you search for a concrete slab calculator, concrete footing calculator, or concrete yard calculator, this tool covers all of them in one place.

Concrete shapes

Unit systems

Currencies

Volume units

How much concrete do I need? Enter your dimensions, pick a shape, and the calculator handles conversions, waste factor, and optional cost estimates — giving you a ready-to-order quantity rounded to standard delivery increments.

How to Use the Concrete Calculator

Step-by-step guide to get accurate concrete estimates

Pick a shape

Choose slab/pad, wall, footing, round column, square column, stairs, or curb from the dropdown at the top of the inputs panel.

Set your units

Switch between imperial (ft/in) and metric (m/cm) using the unit toggles. All dimensions convert automatically when you change units.

Enter dimensions

Fill in length, width, thickness (or diameter, height, etc.) for your selected shape. Fields update in real time as you type and support backspace-to-clear.

Adjust quantity

If you have multiple identical pours (e.g., several footings or columns), increase the quantity using the stepper buttons or type directly.

Set waste factor

Waste is on by default at 10%. Adjust the slider to add extra for cuts, spillage, and uneven forms — the result updates instantly.

Add bag & cost estimates

Toggle Bag & cost estimate to enter bag size, bag yield, bag price, ready-mix price, and concrete density for weight and cost breakdowns.

Read your results

Total volume appears in the hero card in yd³, ft³, and m³. The Order & cost summary shows suggested order quantity, bag count, weight, and cost comparisons.

Concrete Volume Formulas

Core formulas used for slabs, columns, stairs, and more

The calculator uses standard volume formulas and applies unit conversions. These are the same formulas contractors use when they calculate concrete by hand.

Rectangular slab, footing

Volume = Length × Width × Thickness

Use consistent units — all feet or all inches, then convert.

Wall

Volume = Length × Height × Thickness

Height is the vertical wall height. Thickness is the wall width (e.g., 6 in or 8 in).

Curb / beam

Volume = Length × Width × Height

All three dimensions in the same unit. Unlike slabs, curbs use height instead of thickness.

Round column / tube

Volume = π × (Diameter ÷ 2)² × Height

Diameter and height in the same unit before squaring.

Square column

Volume = Side Length × Side Length × Height

Both sides are equal for a square column. Height is the column height.

Stairs (solid, triangular prism)

Volume = Stair Width × Total Run × Total Rise ÷ 2

Total Run = Run per step × step count. Total Rise = Rise per step × step count.

Unit Conversions

1 cubic yard = 27 cubic feet. Divide ft³ by 27 to get yd³.
1 cubic meter = 35.3147 cubic feet. Divide ft³ by 35.3147 to get m³.
For inches: convert to feet first (divide by 12). For cm: convert to meters first (divide by 100).

Bags, Ready-Mix, and Cost Estimates

Compare bagged vs ready-mix and estimate costs

For small pours, bags are convenient. For larger pours, ready-mix is usually cheaper and faster. This calculator estimates bag count using the yield per bag and compares cost if you enter prices. If you're searching for a concrete cost calculator or concrete bag calculator, the pricing panel handles both.

Bag count

Rounded up to next whole bag. Yield varies by bag size.

Total volume ÷ yield per bag

Ready-mix cost

Best for large pours ≥ 1 yd³ or 1 m³.

Volume (yd³ or m³) × price per yard/m³

Bagged cost

Good for small patch jobs under 0.5 yd³.

Bag count × price per bag

Total weight

~150 lb/ft³ (2,400 kg/m³) for standard concrete.

Volume × concrete density

Concrete Calculator Examples

Sample pours with volume and waste included

Patio Slab

1.23 yd³

10 ft × 10 ft × 4 in

With 10% waste: 1.36 yd³

Strip Footing

1.48 yd³

20 ft × 2 ft × 1 ft

With 10% waste: 1.63 yd³

Round Column

0.23 yd³

12 in Ø × 8 ft

With 10% waste: 0.26 yd³

Retaining Wall

1.78 yd³

12 ft × 8 ft × 6 in

With 10% waste: 1.96 yd³

Assumptions and Waste Factor

Why waste is included and how rounding works

10%

Default waste factor

Ganak defaults to a 10% waste factor to cover spillage, uneven forms, and finishing losses. You can toggle waste off or adjust the slider from 0–50%.

The suggested order rounds to common delivery increments (0.25 yd³ for imperial, 0.1 m³ for metric). Rounding up avoids short pours and costly partial loads — especially important when placing a ready-mix order.

Common Mistakes to Avoid

Quick checklist to prevent short pours

Forgetting slab thickness or mixing feet with inches / meters with centimeters.

Using interior dimensions instead of form dimensions.

Skipping waste allowance for uneven subgrades, spillage, or form loss.

Not multiplying by quantity for repeat pours like posts, steps, or columns.

Pro Tips for Accurate Orders

Small habits that improve accuracy and reduce waste

Measure twice and keep units consistent throughout.

Use the bag yield printed on the mix label for best accuracy.

Order ready-mix for large pours; bags for small patch jobs.

When in doubt, round up your order to the next delivery increment.

Frequently Asked Questions

Common questions and detailed answers

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Last updated Jun 28, 2026