Slab Calculator
Driveways, patios, garage floors, shed bases and flat pads.
Plan it. Pour it. Get it right.
Accurate concrete calculators and estimators.
Calculate volume, ready-mix bags, waste allowance and estimated cost for slabs, footings, post holes, walls and more. Fast, free and built for phones.
✓ US & metric units
✓ No sign-up
✓ Includes waste
✓ Works offline after loading
100% free
Mobile friendly
No account needed
Fast estimates
Concrete toolkit
Choose your project.
Every calculator uses the same clear workflow. Enter the dimensions, add a sensible waste allowance and get volume, bags and cost.
Footing Calculator
Continuous strip footings and foundation trenches.
Post Hole Calculator
Fence posts, deck posts, signs and mailbox posts.
Wall Calculator
Concrete walls, retaining walls and foundation walls.
Column Calculator
Round or square concrete piers and columns.
Stair Calculator
Estimate concrete for a simple solid staircase.
Bag Calculator
Convert your required volume into 40, 60 or 80 lb bags.
Rebar Estimator
Estimate grid bars and total linear feet for a slab.
Concrete Cost
Estimate ready-mix or bagged concrete project cost.
Live calculator
Concrete slab calculator
Enter the slab dimensions below. The estimate includes your chosen waste allowance.
Your estimate
0.00 yd³
Enter your measurements to calculate.
- Before waste0.00 yd³
- Waste allowance10%
- 80 lb bags0
- 60 lb bags0
- Estimated material cost$0.00
This is a planning estimate, not a structural specification. Confirm dimensions, mix requirements, reinforcement, access and supplier minimums before ordering.
Built for real projects
Fewer guesses. Less waste. Better pours.
Concrete is expensive to over-order and disruptive to run short on. ConcreteCount gives you a transparent starting estimate, with waste, bags and price shown separately.
- Use the exact finished dimensions.
- Allow extra for uneven sub-base and spillage.
- Check ready-mix minimum load and short-load fees.
- Never use a volume calculator as a structural design substitute.
Practical guides
Before you order concrete.
How much waste should I add?
Five percent may suit neat formed work. Ten percent is a safer general allowance. Irregular excavation may need more.
Common slab thicknesses
Patios and walkways are often around 4 inches. Vehicle loads, poor ground or local requirements may demand more.
Ready-mix or bags?
Bags suit small jobs. Ready-mix usually makes more sense once the bag count, labour and consistency become impractical.
Prepare the sub-base
Remove soft material, compact the base and make sure the formwork is square, level and firmly supported.
Plan the pour
Confirm access, labour, weather, tools, finishing method and where any leftover concrete can safely go.
Curing matters
Concrete gains strength through curing. Protect fresh work from rapid drying, freezing, heavy rain and premature loading.
FAQ
Concrete calculator questions.
How do I calculate concrete for a slab?
Multiply length by width by thickness using consistent units. Convert the result into cubic yards or cubic metres, then add waste.
How many 80 lb bags are in one cubic yard?
Approximately 45 bags at a typical yield of about 0.60 cubic feet per bag. Product yield varies, so check the bag label.
Should I always add 10% waste?
Ten percent is a useful general planning allowance, but neat forms may need less and rough excavations may need more.
Can this calculator design a foundation?
No. It estimates material quantity only. Structural dimensions, reinforcement and mix specification should follow approved plans and local requirements.
Why can supplier totals differ?
Suppliers may round loads, apply minimum quantities, use different bag yields, add delivery charges or recommend extra allowance based on the project.
Important: Calculations are approximate. Always verify measurements and consult the relevant supplier, plans, building authority or qualified professional before ordering or building.