Concrete Calculator
Use this concrete calculator to estimate how much concrete you need for slabs, footings, and fence or deck post holes. The tool converts project dimensions into cubic feet, cubic yards, cubic meters, common bag counts, and optional cost estimates so you can compare bagged concrete with bulk delivery before you buy.
Length in feet
Width in feet
Thickness in inches
Select bag size to calculate bag cost
Leave empty to skip bag cost calculation
Leave empty to skip bulk cost calculation
Typical: 10% for slabs, 5% for post holes
Volume (Cubic Feet)
36.67
includes 10% waste
Volume (Cubic Yards)
1.36
standard bulk order unit
Volume (Cubic Meters)
1.04
metric equivalent
40 lb Bags
123
bags needed
50 lb Bags
98
bags needed
60 lb Bags
82
bags needed
80 lb Bags
62
bags needed
Formula:
Volume = Length × Width × (Thickness ÷ 12)
Assumptions:
- Standard concrete mix (not high-strength or specialty)
- Bag yields: 40lb=0.30, 50lb=0.375, 60lb=0.45, 80lb=0.60 cu ft
- Waste factor accounts for spillage and uneven surfaces
Planning estimate only
These calculations provide planning estimates. Always verify with product specifications, local building codes, and professional guidance before purchasing materials.
What this concrete calculator does
Use this concrete calculator to estimate how much concrete you need for slabs, footings, and fence or deck post holes. The tool converts project dimensions into cubic feet, cubic yards, cubic meters, common bag counts, and optional cost estimates so you can compare bagged concrete with bulk delivery before you buy.
Material Tally calculators are built for planning conversations with suppliers, contractors, and family members before a project starts. They help you see the difference between exact math and practical buying quantities, including waste factors and rounded purchase units. The result should be treated as a strong planning estimate, then checked against product labels, supplier guidance, and local building requirements.
Best for
- Early material planning before visiting a supplier
- Comparing cost assumptions and waste factors
- Checking whether a project is small enough for bagged or boxed materials
- Creating a clearer shopping list before work begins
How to use the calculator
Choose slab/footing mode for rectangular pours or post-hole mode for round holes.
Enter the measured length, width, and thickness, or the post-hole diameter, depth, and quantity.
Select a concrete bag size if you plan to buy bagged mix from a home center.
Add a waste factor to cover uneven excavation, spillage, and small measuring errors.
Review cubic yards, bag counts, and optional cost estimates before ordering materials.
How the math works
For slabs and footings, the calculator multiplies length by width by thickness converted from inches to feet. For post holes, it uses the cylinder formula: pi times radius squared times depth, multiplied by the number of holes. The selected waste percentage is added after the base volume is calculated. Bag counts are rounded up because concrete is sold in whole bags and running short during a pour is more expensive than having a little extra.
Planning tips
Measure the actual excavation, not only the planned drawing size. A slab that is dug half an inch deeper across the whole area can require noticeably more concrete.
Use a higher waste factor when forms are uneven, soil is loose, or the pour includes thickened edges. Smaller pours often need a little extra cushion because one partial bag can make the difference between finishing cleanly and stopping short.
Bulk concrete is usually priced by the cubic yard, while bagged concrete is easier for small repairs and post holes. Compare both outputs if your project is close to the point where delivery might be worthwhile.
Before pouring structural work, confirm local code requirements, reinforcement details, frost depth, and footing dimensions with a qualified professional.
Frequently asked questions
Related tools and guides
Related calculators
- Fence Post Calculator
Plan your fence project start to finish. Calculate post spacing, hole dimensions, concrete bag counts, and total material cost for wood, vinyl, or privacy fences. Start estimating now.
- Gravel Calculator
Get the right amount of gravel for your driveway, path, or base layer. Calculate cubic yards, tons, compaction-adjusted volume, and delivery cost in minutes. Try the free gravel calculator now.
- Paint Calculator
Estimate the exact gallons of paint you need for any room. Factor in doors, windows, coats, coverage rate, and waste so you buy only what you need. Try the free paint calculator now.
- Flooring Calculator
Calculate the right amount of flooring for any room. Enter dimensions, choose material type, and get waste-adjusted square footage, box counts, and cost estimates instantly. Start planning your project now.
- Mulch Calculator
Plan your landscaping with confidence. Estimate mulch in cubic yards, cubic feet, or bags for garden beds and tree rings including waste and cost. Get your precise material list now.
Related guides
- How to Estimate Concrete for a Slab
Learn how slab thickness, form size, waste factor, and cubic-yard conversion affect a concrete order.
- Concrete Slab Prep and Ordering Checks
Run through the form, base, access, reinforcement, and ordering questions that matter before you schedule a concrete slab pour.
- Concrete Bags vs Ready-Mix: Which Should You Use?
Compare bagged concrete and ready-mix delivery for cost, labor, timing, waste, and project size.
- Estimating Waste by Material Type
Choose better waste factors by separating breakage, cuts, spillage, compaction, and product packaging across material types.