Concrete Calculator

Quick tools

Set units once. Reopen recent results anytime.

Scenario presets

Pick the pour that matches the job

Use a slab, footing, post, or step preset.

Project fit

Choose the pour method before you order concrete

Volume matters. Delivery method, reinforcement, and pour sequence matter too.

Bag mix

Best for repairs, isolated footings, and tiny pours where delivery minimums make ready-mix wasteful.

•Low setup complexity
•Good for patch work
•Labor climbs fast past 1 cubic yard

The labor and mix consistency penalty shows up earlier than many DIYers expect.

Ready-mix

Best for slabs, larger pads, and any pour where consistency, timing, and finish quality matter.

•Cleaner yard-to-order conversion
•Better for multiple helpers
•Usually wins on larger projects

Requires form readiness, access, and a realistic unloading plan before the truck arrives.

Reinforcement-aware plan

Best when crack control, load, or edge performance matters as much as concrete volume.

•Check rebar or mesh before ordering
•Review joints and thickened edges
•Match PSI to use case

A perfect yardage number still fails the job if reinforcement and curing are guessed too late.

Why this section helps

Use this section to choose between bags, ready-mix, and reinforcement before you buy.

Fast planning rules

Start with the concrete rules that change the order

Compare yards, bags, and ready-mix before you book the pour.

10x10 slab at 4 in. thick

That slab needs about 1.23 cubic yards of concrete before you adjust for waste, edge thickening, or uneven subgrade.

Many crews add a waste factor so the final order lands closer to the real pour conditions on site.

80-lb bags per cubic yard

One cubic yard is roughly 45 bags of 80-lb concrete mix, which is why ready-mix usually wins once projects get bigger.

The bag count changes slightly by product yield, so compare the actual coverage printed on the mix you buy.

When ready-mix beats bags

Projects over about 1 cubic yard often become more practical with ready-mix because the labor, consistency, and total cost usually improve.

Small repairs and isolated footings still make sense with bags when delivery minimums are too high.

What is a concrete calculator? A concrete calculator determines the precise volume of concrete needed for slabs, footings, and walls in cubic yards or bags (40, 60, or 80 lbs). It prevents ordering too little or too much material by accounting for dimensions, waste factor, and project type.

How to Use This Concrete Calculator

This calculator tells you exactly how much concrete you need. It works for patios, fence posts, and foundations. Get volume in cubic yards (for ready-mix) and bag counts (for DIY).

Step 1: Select Your Project Type

Different projects have different needs. Pick yours:

Slab/Patio/Driveway - Flat surfaces with uniform thickness
Footing/Foundation - Below-grade support, typically deeper
Wall/Retaining Wall - Vertical structures needing forms
Column/Post - Cylindrical shapes (diameter × height)
Steps/Stairs - Stepped structures with multiple levels
Curb/Border - Linear edge structures

Step 2: Enter Your Dimensions

For rectangles, enter length, width, and depth. For columns, enter diameter and height. Use feet for length/width. Use inches for depth/thickness.

Common slab thicknesses:

4 inches - Patios, sidewalks, foot traffic only
5-6 inches - Driveways, garage floors, residential use
8+ inches - Heavy equipment, commercial use

Step 3: Choose Concrete Strength

Strength is measured in PSI. This is the compressive strength after 28 days:

2,500 PSI - Interior floors, non-structural work
3,000 PSI - Standard residential, most common choice
3,500 PSI - Driveways, sidewalks, exterior slabs
4,000 PSI - Commercial projects, heavy vehicle traffic
4,500+ PSI - High-strength and industrial use

Understanding Concrete Volume

Concrete sells two ways:

Ready-Mix Concrete comes by truck. It sells by the cubic yard. One cubic yard = 27 cubic feet. That covers about 80 sq ft at 4" thick. Use ready-mix for projects over 1 cubic yard. It costs less and has consistent quality.

Bagged Concrete comes in 40, 60, and 80-lb bags. An 80-lb bag makes about 0.6 cubic feet. For small projects under 1 cubic yard, bags work well. But mixing by hand is hard work.

Concrete Coverage & Bag Calculator Table

Use this table to quickly estimate bags needed for common slab sizes at 4" thickness:

Slab Size	Cubic Feet	Cubic Yards	80-lb Bags	60-lb Bags
4' × 4'	5.3	0.20	9	12
6' × 6'	12.0	0.44	20	27
8' × 8'	21.3	0.79	36	48
10' × 10'	33.3	1.23	56	74
12' × 12'	48.0	1.78	80	107
16' × 16'	85.3	3.16	142	190
20' × 20'	133.3	4.94	222	296

*Includes 10% waste factor. Based on 4" slab thickness. 80-lb bag = 0.6 cu ft, 60-lb bag = 0.45 cu ft.

Concrete Strength (PSI) Selection Guide

PSI Rating	Best For	Typical Cost/Yard	Cure Time
2,500 PSI	Interior floors, patios, light residential	$120-140	28 days
3,000 PSI	Standard residential, foundations, walls	$130-150	28 days
3,500 PSI	Driveways, sidewalks, pool decks	$140-160	28 days
4,000 PSI	Commercial floors, heavy traffic areas	$150-175	28 days
4,500+ PSI	Industrial, high-rise, precast	$165-200+	28 days

Why Add a Waste Factor?

Always order 10% extra. This covers:

Low spots in the subgrade needing more material
Spillage during pouring and finishing
Form irregularities and expansion
Running short mid-pour (cold joints)

Running out mid-pour is a disaster. It creates weak "cold joints" that crack and fail. Always order more than you think you need.

Reinforcement: Rebar vs. Wire Mesh

Concrete handles compression well but not tension. Reinforcement stops cracking:

Wire Mesh - A 6x6" grid pattern. Good for slabs and patios. Place it in the middle third of the slab.

Rebar - Steel bars for structural work. Use #4 rebar (1/2" diameter) at 12" spacing for footings and thick slabs.

Fiber Reinforcement - Synthetic fibers mixed in. Controls shrinkage cracks. A good addition but not a replacement for steel.

Ready-Mix vs. Bags: Which to Choose?

Factor	Ready-Mix	Bags
Best For	1+ cubic yards	Under 1 cubic yard
Cost per Yard	$125-170	$200-300
Quality	Consistent mix	Varies with mixing
Labor	Less physical	Very labor-intensive
Time	Fast delivery	Slow mixing

Tips for a Successful Pour

Prepare the subgrade - Compact soil, add 4" gravel base for drainage
Build strong forms - Use 2x4 or 2x6 lumber, stake every 2-3 feet
Check the weather - Avoid pouring in rain or extreme heat/cold
Have help ready - Concrete waits for no one once mixed
Plan your finishing - Have tools ready: screed, float, edger, broom
Cure properly - Keep moist for 7 days, don't walk on for 24-48 hours

How we checked this page

Written by: TheSiteMath Editorial Team

Reviewed by: TheSiteMath editors (formula, source, and update review)

Last reviewed: 2026-03-20

Publisher: TheSiteMath

Scope: U.S. construction material estimating, calculator workflows, and project planning guidance for contractors and homeowners.

What we checked:

• Formulas checked against trade and source material
• Verified against: ACI guidance and standard concrete estimating practices, ASTM concrete references where mix or material specifications matter, Current U.S. concrete pricing benchmarks
• Price ranges used for planning, not as fixed quotes
• Examples checked in the live calculator

Methodology:

• Example quantities and explanations on this page are cross-checked against the matching live calculator on TheSiteMath.
• This concrete content is scoped for U.S. planning and estimating workflows, not for stamped engineering or permit approval.
• We review formulas, material assumptions, and practical steps against category-appropriate references before publishing updates.
• We refresh pages when calculator logic, supplier assumptions, or pricing guidance materially changes.
• Readers should confirm final dimensions, structural requirements, and local code obligations with qualified local professionals.

Editorial standards: We review pages before publication and update them when formulas or pricing need a fix. If you spot an issue, please contact us .

For our review process, corrections policy, and monetization disclosure, see the Editorial Standards page.

Concrete FAQ

Concrete ordering questions before you schedule the pour

These questions focus on the practical buying choices behind the math: bags versus ready-mix, pour timing, reinforcement, and realistic yardage use.

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

There are approximately 45 bags of 80-lb concrete in one cubic yard. One 80-lb bag yields about 0.60 cubic feet of concrete. Since a cubic yard is 27 cubic feet: 27 ÷ 0.60 = 45 bags.

How many bags of concrete do I need for a 10x10 slab?

A 10x10 foot slab at 4 inches thick requires approximately 1.23 cubic yards or about 56 bags of 80-lb concrete (with 10% waste factor). For this size, ready-mix delivery is usually more practical.

What's the difference between concrete and cement?

Cement is an ingredient in concrete. Concrete is a mixture of cement (10-15%), water, sand (fine aggregate), and gravel (coarse aggregate). Pre-mixed bags contain all ingredients - just add water.

How long does concrete take to cure?

Concrete reaches about 70% strength in 7 days and near full strength at 28 days. You can walk on it after 24-48 hours, drive on it after 7 days, but avoid heavy loads for 28 days.

Can I pour concrete in cold weather?

Concrete can be poured when temperatures are above 40°F and rising. Below freezing, water in the mix can freeze and damage the concrete permanently. Use blankets, heaters, or accelerators in cold weather.

Should I use ready-mix or bags?

Use ready-mix for projects over 1 cubic yard - it's more economical ($125-170/yard vs $200-300/yard for bags) and ensures consistent quality. Bags work better for small projects under 1 cubic yard.

Free Concrete Calculator