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: May 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.

Reviewed For Methodology, Labels, And Sources

Every CalculatorWallah calculator is published with visible update labeling, linked source references, and founder-led review of formula clarity on trust-sensitive topics. Use results as planning support, then verify institution-, policy-, or jurisdiction-specific rules where they apply.

Reviewed By

Jitendra Kumar, Founder & Editorial Standards Lead, oversees methodology standards and trust-sensitive publishing decisions.

Review editor profile

Topic Ownership

Sales tax and tax-sensitive estimate tools, Education and GPA planning calculators, Health, protein, and screening-formula pages, Platform-wide publishing standards and methodology

See ownership standards

Methodology & Updates

Page updated May 2026. Trust-critical pages are reviewed when official rates or rules change. Evergreen calculator guides are checked on a recurring quarterly or annual cycle depending on topic volatility.

Sources & methodology About the review process

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.

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.