Concrete Calculator

Name: Concrete Calculator
Author: Jitendra Kumar

Estimate concrete for slabs, footings, round piers, columns, and stairs with cubic yards, cubic feet, bag count, cost, and weight outputs.

Last Updated: June 13, 2026

Project type

Length unit

Thickness unit

Extra allowance

Use 5% to 15% for typical waste and subgrade variation.

Length

Width

Slab thickness

Quantity

items

Bag yield

cu ft

An 80 lb concrete bag is commonly about 0.6 cu ft; check your product label.

Price per bag

Ready-mix price

$/ cu yd

Concrete needed

1.63cu yd

Cubic feet

44cu ft

Bags to buy

74bags

Ready-mix estimate

$260.74

Base volume

40 cu ft

Extra allowance

4 cu ft

Bag cost

$481.00

Estimated weight

3.30 tons

Planning item	Estimate	Use this for
Base volume	40 cu ft	Before extra allowance.
Extra allowance	4 cu ft	Added for waste, uneven subgrade, forms, and over-excavation.
Ready-mix order	1.63 cu yd	Useful for truck-delivered concrete quotes.
Bagged concrete	74 bags	Exact estimate is 73.33 bags.

Formula

Concrete volume is area times thickness for slabs and footings, pi x radius squared times height for round piers, and a triangular-prism estimate for stairs.

Bagged concrete

Exact bag count is 73.33. The calculator rounds up to 74 bags.

Delivery note

Ready-mix suppliers may have minimum orders, short-load fees, delivery fees, and scheduling limits beyond the cubic-yard material estimate.

Concrete Planning Notice

This calculator estimates material volume only. Actual concrete needs can change with excavation, forms, subgrade, compaction, reinforcement, slope, thickened edges, spillage, and delivery rules. Structural design, code compliance, frost depth, permits, and load requirements should be reviewed with qualified local professionals.

Checked by Jitendra Kumar

Concrete Calculator is checked for formula labels, source links, and result limits.

Jitendra Kumar, Founder & Editorial Standards Lead. Updated June 13, 2026. Scope: measurement calculators.

Sources & methodology · Review standards

How to Use the Concrete Calculator

Choose the project type, then enter dimensions in the selected units. Slabs and footings use length, width, and thickness. Round piers use diameter, height or depth, and quantity. Stairs use total run, total rise, and width as a triangular-prism estimate.

Enter the bag yield from the product label if you are using bagged concrete. For larger pours, use the cubic-yard result and ready-mix price estimate when requesting quotes.

Step 1: Choose project type
Select slab, footing, round pier or column, or stairs so the correct volume formula is used.
Step 2: Enter dimensions
Input length, width or diameter, thickness, height, or rise in the units shown.
Step 3: Add allowance and pricing
Add a waste allowance, bag yield, bag price, and ready-mix price per cubic yard.
Step 4: Review bags and yards
Use bag count for small projects and cubic yards for ready-mix delivery planning.

How This Concrete Calculator Works

The calculator converts dimensions to feet, applies the selected volume formula, adds the extra allowance percentage, and converts final volume into cubic feet and cubic yards.

Bag quantity is calculated by dividing total cubic feet by your entered bag yield and rounding up to whole bags. Ready-mix cost is estimated by multiplying cubic yards by the entered price per cubic yard.

Estimated weight uses a practical planning assumption of about 150 pounds per cubic foot for normal-weight concrete. Product-specific mixes and aggregates can vary.

Concrete Planning Guide

Concrete Volume Formulas

Project	Formula	Planning note
Slab or pad	Length x width x thickness	Use for patios, walkways, pads, and simple rectangular slabs.
Footing or trench	Length x width x depth	Use structural dimensions from approved plans or local code guidance.
Round pier or column	pi x radius² x height x quantity	Use diameter and depth or height for post holes and piers.
Stairs	Total run x total rise x width / 2	Approximates the stair mass as a triangular prism.

Typical Thickness and Bag Reference

Project	Typical planning range	Important note
Small patio or walkway	3 to 4 inches	Use local code, reinforcement, and subgrade guidance for final design.
Driveway slab	4 to 6 inches	Vehicle loads, soil, reinforcement, and joints matter.
Footing	Project-specific	Depth and width should follow code, frost, soil, and structural requirements.
Round pier	Project-specific	Diameter and depth depend on load, soil, frost, and post base design.

Concrete option	Approximate yield	Best use
40 lb bag	About 0.30 cu ft	Small patches and very small pours.
60 lb bag	About 0.45 cu ft	Small slabs, post holes, and repairs.
80 lb bag	About 0.60 cu ft	Common bagged-concrete planning size.
Ready-mix truck	Sold by cubic yard	Usually better for larger pours.

Worked Concrete Examples

Job	Calculation	Planning result
10 ft x 12 ft slab, 4 in thick	10 x 12 x 0.333 = 39.96 cu ft	About 1.48 cu yd before allowance.
Three 12 in diameter piers, 3 ft deep	pi x 0.5² x 3 x 3 = 7.07 cu ft	About 12 bags if each 80 lb bag yields 0.60 cu ft.
40 ft footing, 16 in wide, 8 in deep	40 x 1.333 x 0.667 = 35.57 cu ft	About 1.32 cu yd before waste or form variation.

Bagged concrete is practical for small pads, repairs, short footings, and post holes. Ready-mix delivery is often more practical once the project reaches several dozen bags or needs one continuous pour.

For irregular slabs, split the plan into rectangles, estimate each section, and add the volumes. The Square Footage Calculator can help with area before converting to concrete volume.

Keep the research moving with Square Footage Calculator, Room / Plot / Lot Area & Size Calculator, Volume Converter, and Topsoil Calculator.

Frequently Asked Questions

Multiply slab length by width by thickness, with all dimensions converted to feet. Divide cubic feet by 27 to get cubic yards, then add an allowance for waste and uneven subgrade.

One cubic yard equals 27 cubic feet. Ready-mix concrete is commonly quoted by cubic yard, while bagged concrete is often planned in cubic feet of yield.

If an 80 lb bag yields about 0.6 cubic feet, one cubic yard takes about 45 bags before waste. Always check the yield printed on the exact bag you plan to buy.

A 5% to 10% allowance is common for simple forms. Irregular excavation, uneven subgrade, thickened edges, spillage, or complex forms may need more.

No. This calculator estimates material volume only. Footings, piers, slabs, reinforcement, frost depth, soil bearing, drainage, and permits require local code and qualified professional guidance.

Slab mode uses length x width x thickness after converting all dimensions to feet. The result is cubic feet, and cubic feet divided by 27 gives cubic yards.

Calculate each rectangle separately, add the cubic-foot volumes, then apply the allowance once to the total. This avoids losing volume from small extensions, step-outs, or pads.

Concrete bags are bought as whole bags. If the math says 12.2 bags, the practical purchase quantity is 13 bags before any extra project-specific reserve.

Bagged concrete is practical for small jobs and repairs. Ready-mix is usually more practical when the bag count becomes large or when the pour needs consistent placement time.

Only if you enter them as a separate footing, trench, or extra slab section. A slab with thickened edges should not be treated as one flat rectangle unless the edge volume is minor.

Forms can bow, excavation can be uneven, subgrade can vary, and concrete can be lost during placement. That is why simple pours often include a 5% to 10% allowance.