Concrete Calculator

How to use this concrete calculator

• Pick a shape: slab or pad, footing or wall, round post hole or sonotube, or steps.
• Enter the sizes. For a slab, type the length and width in feet, or the square feet if you already know it.
• For a slab, pick a thickness. Four inches is standard for patios, walks and car driveways.
• Pick the extra for waste and spills: 0%, 5% or 10% (10% is preset). The result shows the exact amount and the amount with extra, then bags in four sizes and cost.

How many bags of concrete do I need?

Quikrete lists these yields for its Concrete Mix: about 0.30 cubic feet per 40lb bag, 0.375 per 50lb, 0.45 per 60lb and 0.60 per 80lb. That works out to 90, 72, 60 or 45 bags per cubic yard.

At 4 inches thick, one bag covers about 0.9 sq ft (40lb), 1.125 sq ft (50lb), 1.35 sq ft (60lb) or 1.8 sq ft (80lb).

60lb vs 80lb bags: three 80lb bags make the same 1.8 cubic feet as four 60lb bags. At Home Depot Turfland the cost per cubic foot is about the same ($11.63 vs $11.64), while Lowe's 60lb price works out to $10.78. Pick 80lb for fewer bags to mix, or 60lb if lifting is a concern.

How much does a yard of concrete cost?

A cubic yard of ready-mix typically costs $119 to $147 (national price). That includes delivery within 20 miles on a full truck of about 10 yards.

Order less than 10 yards and a short-load fee adds about $53 per yard, for about $172 to $200 per yard. Delivery past 20 miles, Saturday delivery and pumping cost extra.

Bags are sold per bag. In Lexington in October 2026, an 80lb bag of Quikrete Concrete Mix was $6.98 at Home Depot, and a 60lb bag $4.85 at Lowe's or $5.24 at Home Depot. A yard's worth of 80lb bags (45) comes to about $314.

For 40lb and 50lb bags, check the shelf price in store. Cost per sq ft at 4 in. is the bag price ÷ 0.9 (40lb) or ÷ 1.125 (50lb).

Here's what that comes to per square foot of slab, concrete only:

Example: a 10x10 ft pad at 4 inches is 100 sq ft, or 1.23 cubic yards exact (1.36 with 10% extra). With the extra, that's 62 80lb bags ($433) or 82 60lb bags ($398 to $430), against $234 to $272 for a short load of ready-mix.

Contractors quote installed work per square foot, and most of that price is labor, forms, base and finishing.

These are planning ranges, not our quotes. For a real number, call 859-927-8679.

Is it cheaper to buy concrete or mix it yourself?

For the same amount of concrete, buying ready-mix costs less than mixing bags yourself. Bags are sold per bag, ready-mix is quoted per cubic yard, and installed work per square foot, so the table shows each one as it's sold, then converted.

At 4 inches, bags come to about $3.59 to $3.88 per sq ft of slab, and a short load of ready-mix about $2.12 to $2.47. Both are concrete only, before forms, base, tools or labor.

The math: a 4 in slab is 1/3 ft thick, so:

• An 80lb bag (0.60 cu ft) covers 1.8 sq ft.
• A 60lb bag (0.45 cu ft) covers 1.35 sq ft.
• A 50lb bag (0.375 cu ft) covers 1.125 sq ft.
• A 40lb bag (0.30 cu ft) covers 0.9 sq ft.
• A cubic yard (27 cu ft) covers 81 sq ft.
• Cost per sq ft = price ÷ coverage, e.g. $6.98 ÷ 1.8 = $3.88 and $172 ÷ 81 = $2.12.

Bags still make sense for small jobs, like fence posts, a mailbox or a small repair, where a truck isn't worth ordering.

For anything bigger, mixing 100 or more bags by hand is hard, slow work, and the slab can set unevenly between batches.

Footing and wall concrete

Choose "Footing or wall." Enter the length in feet, then the width and the depth (or wall height) in inches.

The math: length × (width ÷ 12) × (depth ÷ 12) = cubic feet. Divide by 27 for cubic yards.

Example: a 20 ft footing, 16 in wide and 8 in deep, is 17.78 cu ft (0.66 cu yd) exact. With 10% extra it's 19.56 cu ft (0.72 cu yd): 33 80lb bags or 44 60lb bags.

For load-bearing footings, Quikrete says to follow local building codes. The calculator works out volume only, not the footing size your project needs.

Post hole and sonotube concrete

Choose "Round post hole or sonotube." Enter the diameter and depth in inches, and how many holes or tubes.

The math: 3.1416 × (diameter ÷ 24)² × (depth ÷ 12) × quantity = cubic feet.

Example: ten post holes, 10 in wide and 36 in deep, take 16.36 cu ft (0.61 cu yd) exact. With 10% extra that's 18.00 cu ft: 30 80lb bags, 40 60lb bags or 48 50lb bags.

The result doesn't subtract the post, so it runs a little high. Quikrete's fence post method calls for a hole about 3 times the post's width and about 1/3 of the post's height deep.

Concrete steps

Choose "Steps." Enter the number of steps, the rise (height of each step) and run (depth of each tread) in inches, and the width in feet. Add a top landing if you have one.

The math: each step is solid down to the ground. Steps = width × (run ÷ 12) × (rise ÷ 12) × (1 + 2 + … + number of steps). A landing adds width × (landing depth ÷ 12) × (number of steps × rise ÷ 12).

Example: 3 steps, 7 in rise, 11 in run and 4 ft wide, with a 36 in landing, is 12.83 cu ft of steps plus 21.00 cu ft of landing: 33.83 cu ft (1.25 cu yd) exact. With 10% extra it's 37.22 cu ft (1.38 cu yd): 63 80lb bags or 83 60lb bags.

Steps built over gravel or block fill need less concrete than this.

Concrete cost guides for Lexington

• Concrete Costs in Lexington
• Concrete Slab Cost
• Concrete Driveway Cost
• Concrete Patio Cost

Planning a project? See Concrete Driveways, Patios, Sidewalks & Steps and Stamped & Decorative Concrete.

Concrete calculator FAQs

How many bags of concrete are in a yard?

About 45 80lb bags, 60 60lb bags, 72 50lb bags or 90 40lb bags. Quikrete lists yields of 0.60, 0.45, 0.375 and 0.30 cubic feet per bag, and a cubic yard is 27 cubic feet.

How much concrete do I need for a 10x10 slab?

At 4 inches thick, 33.33 cubic feet, or 1.23 cubic yards exact. With 10% extra, plan on 1.36 yards: 62 80lb bags, 82 60lb bags, 98 50lb bags or 123 40lb bags.

How much does a yard of concrete cover?

A cubic yard is 27 cubic feet. It covers 108 sq ft at 3 inches thick, 81 sq ft at 4 inches, 64.8 sq ft at 5 inches and 54 sq ft at 6 inches.

How many bags of concrete are on a pallet?

Home Depot lists Quikrete Concrete Mix pallets of 42 80lb bags or 56 60lb bags, and says counts can vary by store, so call ahead. Quikrete's product guide lists 80 bags per pallet for 40lb bags. A pallet of 80lb or 60lb bags makes about 25.2 cubic feet, just under a yard.

How much does a 50 lb bag cover?

Quikrete lists about 0.375 cubic feet per 50lb bag of Concrete Mix. That covers about 1.125 sq ft at 4 inches thick, or 2.25 sq ft at 2 inches, the thinnest pour Quikrete lists for this mix. You need 72 of them for a cubic yard.

How thick should a concrete driveway be?

At least 4 inches for cars, and 5 to 6 inches for heavier vehicles (HomeGuide).

How much extra concrete should I order?

HomeGuide suggests 5% to 10% extra for waste and spills. This calculator adds 10% unless you pick 5% or 0%, and always shows the exact amount too.

How do I get a quote instead?

Call 859-927-8679 or send the quote form. Your request goes to a local Lexington concrete contractor, who follows up to set a time for a free on-site estimate.

Rather have it poured for you?

A free on-site look gets you an actual price. Call 859-927-8679 or send the quote form, and a local Lexington concrete contractor will follow up.