Concrete Calculators
Concrete Calculators
Every concrete calculation you need — slabs, footings, round columns, post holes, CMU blocks, driveways, and cost estimates. Industry-standard formulas, QUIKRETE-spec bag yields.
Getting Concrete Right the First Time
Concrete is one of the few materials where running out mid-pour isn't just inconvenient — it can ruin the entire project. A cold joint (where fresh concrete meets partially cured concrete) creates a structural weak point that no amount of patching fully fixes. Ordering too much wastes money. Ordering too little means stopping the pour, calling for more, and hoping the first batch hasn't started setting.
The calculators below cover every common concrete project, from a small post hole to a full driveway pour. Each one uses QUIKRETE-specification bag yields (0.45 cu ft per 60 lb bag, 0.60 cu ft per 80 lb bag) and standard geometry formulas. Enter your dimensions, and you'll know exactly what to order — in cubic yards for ready-mix delivery, or in bag counts if you're mixing by hand.
Every calculator includes a built-in waste factor recommendation. Most contractors add 5–10% to the calculated volume. Subgrade irregularities, forms that flex slightly, and concrete that sticks to the mixer all eat into your total.
Which Calculator Do I Need?
If you're pouring a patio, walkway, garage floor, or shed pad, use the Slab Calculator. It's optimized for flat rectangular pours and includes thickness recommendations for different applications.
If you're setting fence posts or deck posts, use the main Concrete Calculator in post hole mode. Enter hole diameter, depth, and the number of posts, and it returns bag counts — usually the most practical unit for post-setting work.
If you're building a retaining wall, garden wall, or foundation pier, the Block Calculator handles CMU (concrete masonry unit) layouts. It calculates block count, mortar bags, and courses for five standard block sizes.
If you're budgeting a project and need a cost estimate before committing, start with the Cost Calculator. It shows the price difference between bags and ready-mix delivery at various project sizes — the crossover point where ready-mix becomes cheaper is often lower than people expect.
If you already know your volume and just need to convert between cubic yards, cubic feet, and bags, the Bag Calculator does that conversion quickly.
Bags vs. Ready-Mix: The Crossover Point
Ready-mix concrete (delivered by truck) typically costs $120–$200 per cubic yard. An 80 lb bag at $6.50 yields 0.60 cubic feet — that works out to roughly $290 per cubic yard in bags. The math is clear: ready-mix is cheaper per yard. But ready-mix comes with minimum order fees, short-load surcharges, and a countdown clock once the truck arrives.
For most homeowners, the practical crossover is around 1 cubic yard (about 45 bags of 80 lb mix). Below that, bags are simpler even though the per-yard cost is higher. Above that, the savings from ready-mix delivery justify the logistics. The Cost Calculator shows this breakpoint for your specific project size.
Quick Reference: Coverage by Thickness
Coverage per Cubic Yard
4-inch slab: 81 sq ft per yard
5-inch slab: 65 sq ft per yard
6-inch slab: 54 sq ft per yard
8-inch slab: 40 sq ft per yard
These numbers assume a flat, level subgrade. Uneven ground increases concrete consumption — that's where the 5–10% waste factor matters most.
Related Materials
Most concrete projects require prep work and complementary materials. A slab or driveway needs a compacted gravel base — typically 4 inches of crushed stone beneath the pour. Fence posts need proper burial depth before concrete is placed around them. And if you're building a block wall, you'll want to calculate sand for the mortar mix separately.