Concrete Calculator for Cubic Yards & Cost

Length (ft)

Width (ft)

Thickness (in)

Quantity

Volume Needed: 0.00 cu yd

Bags Required: 0 bags

Total Weight: 0 lbs

Estimated Cost: $0.00

Concrete Type

Bag Size

Waste Factor (%)

Recommended: 5-15% for typical projects

How to Use This Concrete Calculator

This concrete calculator for cubic yards helps you estimate ready-mix concrete, premix bags, and rough project cost for slabs, walls, columns, curbs, stairs, and footings. Enter the job dimensions, choose the mix details, and use the final volume as your ordering baseline.

Pick the Shape

Select the tab that matches your project, such as a slab, wall, footing, round column, curb section, or staircase.

Enter Dimensions

Measure carefully and enter length, width, depth, height, diameter, or step values exactly as your forms or excavation are laid out.

Set Bag Size and Waste

Choose the concrete type, pick the bag size you want to compare, and add a realistic waste factor for overage and cleanup.

Review the Estimate

Check the final cubic yards, bag count, total weight, and estimated cost before you buy materials or call a ready-mix supplier.

Practical Measurement Tips

Measure the Actual Pour Area

Use the inside dimensions of the forms or excavation rather than rough plan dimensions so your cubic feet estimate matches reality.

Convert Inches Before Manual Math

Thickness, width, and footing depth are often measured in inches, so convert them to feet before calculating cubic yards by hand.

Break Odd Shapes Into Simple Parts

For L-shaped slabs, stepped pads, or irregular footings, calculate each rectangle, triangle, or cylinder separately and add them together.

Keep a Waste Buffer

Simple pours often use 5% to 10% extra, while curved forms, hand mixing, or uneven subgrade may justify 10% to 15%.

Understanding Your Results

Your results help you decide whether to use ready-mix concrete or premix bags, how much buffer to keep, and whether the project still fits your budget before you order.

Volume Needed

This field shows the final volume in cubic yards after waste is added. Because ready-mix suppliers sell by the cubic yard, this is usually the number you need when you request pricing or delivery.

Bags Required

The bag estimate helps you compare bagged concrete with ready-mix. If the count is very high, the labor of mixing by hand may cost more than the materials seem to save.

Total Weight

The total weight gives you a better picture of handling and transport. Even small increases in slab thickness can add hundreds of pounds to a hand-mixed job.

Estimated Cost

The cost estimate is best used for quick budgeting and comparing mix types. Your final total may still change because of taxes, delivery, reinforcement, base prep, and finishing supplies.

How Pros Read the Estimate

Start with cubic yards, because that is the number most suppliers care about. If the job is well under half a cubic yard, bags may be practical. Once you get near a full yard, ready-mix often becomes the better option because the labor of mixing, placing, and cleaning up dozens of bags adds up quickly.

Then look at the waste factor. Neat forms on compacted base can often use a smaller margin, while stairs, footings, curved forms, and uneven excavations usually justify more. Finally, compare cost with bag count and weight together so you do not choose a cheap material option that creates an expensive labor problem.

Used this way, the calculator is not just a volume tool. It is a planning tool for materials, delivery, labor, and budget.

The Formula Explained

If you want to know how to calculate concrete manually, the key is to find the volume in cubic feet first and then divide by 27. The right formula depends on whether your shape is rectangular, cylindrical, or stepped.

Slabs, Pads, and Simple Footings

Cubic Yards = (Length x Width x Depth in feet) / 27

This rectangular formula works for patios, driveways, sidewalks, garage floors, and simple footings. If your thickness is measured in inches, divide by 12 before you multiply.

For example, a 4-inch slab is 0.333 foot thick. That small conversion step is what keeps cubic feet and cubic yards accurate.

Walls and Curb Sections

Cubic Yards = (Length x Height x Thickness in feet) / 27

Concrete walls are basically slabs turned vertical. A curb-and-gutter profile can be estimated as two rectangles added together before you convert to cubic yards.

This approach is much cleaner than guessing from overall dimensions that include empty space or changing thickness.

Columns, Sonotubes, and Round Piers

Cubic Yards = (pi x radius squared x height) / 27

Use the cylinder formula whenever the concrete pour is round. Measure the diameter, divide by two for radius, square the radius, then multiply by height.

This is the standard method for deck piers, structural columns, and round footings.

Worked Example With Real Numbers

Suppose you are pouring a 20 ft by 20 ft driveway at 5 inches thick. Convert the thickness first: 5 / 12 = 0.417 foot. Then multiply 20 x 20 x 0.417 = 166.8 cubic feet.

Now divide by 27. That gives you 6.18 cubic yards before waste. Add a 10% waste factor and the order becomes about 6.80 cubic yards.

If you compared that to premix bags, you would be looking at roughly 306 bags of 80 lb concrete. That is why driveway-sized pours usually move quickly into ready-mix territory.

Common Use Cases & Tips

These examples show how concrete volume, bag yield, and waste factor work in the kinds of pours people estimate most often.

10 x 10 Patio Slab

A 10 ft by 10 ft patio at 4 inches thick needs about 1.23 cubic yards before waste and about 1.36 cubic yards with a 10% waste factor.

Tip: 4 inches is common for patios, but always confirm subgrade quality and whether reinforcement is needed.

20 x 30 Driveway

At 4 inches thick, a 20 ft by 30 ft driveway uses about 7.41 cubic yards before waste. With a 10% buffer, it becomes roughly 8.15 cubic yards.

Tip: if the driveway will carry trucks or frequent heavy vehicles, consider 5 to 6 inches and a stronger PSI rating.

Fence Posts and Small Piers

A round footing 12 inches in diameter and 3 feet deep uses about 0.087 cubic yard. Four of them total about 0.35 cubic yard before waste.

Tip: jobs like this are often ideal for premix bags because the total volume is small and access may be tight.

Continuous Footing

A footing 40 feet long, 16 inches wide, and 8 inches deep is about 1.65 cubic yards before waste and about 1.81 cubic yards after a 10% waste factor.

Tip: excavated footings are rarely perfect, so a realistic waste factor matters more here than it does on a square patio form.

Sidewalk Section

A sidewalk 30 feet long, 4 feet wide, and 4 inches thick comes out to about 1.48 cubic yards before waste and about 1.63 cubic yards after a 10% buffer.

Tip: check slab thickness at several points because long narrow pours can drift deeper than expected.

Concrete Stairs

Stairs often surprise people because the stair body, landing, and thickened base can all add volume fast. They are one of the easiest shapes to underestimate.

Tip: calculate the triangular stair body and any platform separately so you do not miss part of the pour.

Field Tips That Save Money

Round your order thoughtfully. Coming up short is usually more expensive than a small leftover amount.

Do not choose slab thickness by guesswork. Thickness changes volume, PSI needs, reinforcement, and cost at the same time.

Use cubic yards for supplier calls and bag counts for labor planning.

Check curing time, weather, and finish method before you assume the project can be poured in a single easy session.

Bag Sizes, Ready-Mix Orders, and Concrete Thickness Guide

Competitor pages often skip the buying decision after the calculator. This section fills that gap so you can move from cubic yards to an actual order plan.

Bagged Concrete vs Ready-Mix

Bagged concrete makes sense for repairs, fence posts, small pads, deck supports, and pours where delivery access is poor. It is flexible, but labor-intensive once the bag count gets high.

Ready-mix concrete is usually the better choice for slabs, driveways, garage floors, walls, and long footings. It saves mixing time, gives more consistent quality, and is easier to place on larger pours.

A useful rule is that once the project gets close to one cubic yard, ready-mix often starts winning on labor and consistency even if the bag price seems cheaper at first.

Truck Loads and Ordering Margin

Many ready-mix trucks carry around 8 to 10 cubic yards, though the exact amount depends on the truck and local hauling limits. Small orders may trigger a short-load fee, so supplier pricing matters as much as raw yardage.

This is why the waste factor is so important. A shortage can force a second trip, delay finishing, or leave a cold joint. A small cushion is usually cheaper than coming up short.

If your estimate lands near a supplier minimum, compare the short-load fee with the real labor cost of mixing many extra bags by hand.

Quick Reference Table

Project	Typical Thickness	Common PSI	Ordering Note
Patio	4 inches	3000 PSI	Good candidate for simple slab math and moderate waste factor.
Sidewalk	4 inches	3000 PSI	Long pours should be checked in several spots for depth drift.
Driveway	4 to 6 inches	3000 to 4000 PSI	Often worth calling a ready-mix supplier rather than mixing bags.
Garage Floor	4 to 6 inches	3500 to 4000 PSI	Check point loads if vehicles or heavy equipment will sit on the slab.
Footing	Varies by design	3000 to 4000 PSI	Confirm footing dimensions with local code or engineering plans.
Stairs	4 to 6 inches	3000 to 4000 PSI	Calculate stairs and landing separately for a cleaner estimate.

Typical Bag Yield Guidance

As a rough reference, one cubic yard often equals about 45 bags of 80 lb premix, around 60 bags of 60 lb mix, or roughly 90 bags of 40 lb mix. The exact yield depends on the product, so check the bag label if you are buying in bulk.

This page calculates concrete only. It does not include forms, gravel base, rebar, wire mesh, vapor barrier, finishing tools, or delivery charges. Keep those items in your final budget.

Use the calculator as the starting point, then confirm the final order with your supplier if the job size, reinforcement, or local requirements are significant.

Frequently Asked Questions

These question-based answers target the same practical topics people search before they buy concrete.

Multiply the length, width, and depth in feet to get cubic feet, then divide by 27. If any dimension is in inches, convert it to feet before you multiply.

You need about 1.23 cubic yards before waste. If you add a 10% waste factor, plan for about 1.36 cubic yards.

A cubic yard usually takes about 45 bags of 80 lb premix. Always compare that baseline with your waste factor and the actual yield listed by the bag manufacturer.

Bagged concrete is usually best for small repairs, posts, and tiny pads. Ready-mix is often better for larger slabs, walls, footings, and driveways because it saves labor and gives consistent mix quality.

Many residential projects use 5% to 10%. Uneven excavation, stairs, curves, or hand-mixed work may justify closer to 10% to 15%.

A typical residential driveway is often poured at 4 inches, but heavier vehicles or weaker subgrade may need 5 to 6 inches. Always verify local code and project conditions.

Normal-weight concrete is commonly estimated at about 4,000 pounds per cubic yard. The exact number depends on aggregate, water content, and the mix design.

Many ready-mix trucks carry around 8 to 10 cubic yards, but delivery limits vary. Ask your local supplier about truck capacity, short-load fees, and scheduling.

Concrete Calculator for Cubic Yards