Primary material
62 bags
80 lb concrete mix
Use the calculated bag count as your buying starting point, then verify yield and pallet limits with the store.
Concrete slab calculator
Concrete slab calculator for yards, bags, and material cost.
Enter slab length, width, thickness, and waste allowance to estimate cubic yards, 80 lb bags, 60 lb bags, and bagged vs ready-mix material cost.
10 x 10 x 4 in
1.36 yd³
62 bags at 80 lb
Default, editable waste
10%
Adjustable to 5% or 15%
Formula
L x W x T
Thickness converted to feet
Quick slab answers
Common slab sizes
10 x 10 patio
10 ft x 10 ft x 4 in
1.36 yd³
62 bags at 80 lb with default 10% waste
See the full 10 x 10 breakdown →12 x 12 shed pad
12 ft x 12 ft x 4 in
1.96 yd³
88 bags at 80 lb with default 10% waste
See the full 12 x 12 breakdown →20 x 20 garage
20 ft x 20 ft x 4 in
5.43 yd³
245 bags at 80 lb with default 10% waste
See the full 20 x 20 garage breakdown →24 x 24 two-car garage
24 ft x 24 ft x 6 in
11.73 yd³
528 bags at 80 lb with default 10% waste
See the full 24 x 24 two-car garage breakdown →When ready-mix starts to make sense
If the result shows dozens of bags, compare bagged material cost against ready-mix delivery. Larger slabs are usually easier to place consistently with ready-mix.
Shopping list
Ready to price and order
Use the calculated quantities as a starting cart, then compare store availability, delivery fees, pallet limits, and local ready-mix minimums before buying.
Large pours
Ready-mix quote check
For high bag counts, compare the bagged route against local ready-mix minimums, delivery, access, and unload time.
Optional base
Gravel base
Base depth is project-specific. Estimate it separately before adding bags or bulk gravel to the order.
Optional forms
Forms and stakes
Plan lumber, stakes, screws, release, and bracing around the perimeter and any step-downs or curves.
Store buttons open retailer search results for now. Confirm exact product yield, pickup, delivery, and pallet rules before ordering.
Formula shown
How the slab calculation works
1. Slab volume in cubic feet
length ft x width ft x (thickness in / 12)
2. Convert to cubic yards
cubic yards = cubic feet / 27
3. Add waste and estimate bags
bags = ceil(cubic feet x (1 + waste) / bag yield)
Slab-specific edge cases
Slabs are sensitive to subgrade prep. A low spot, deeper edge, or thickened perimeter can add volume quickly. If your slab has beams, haunches, or a sloped base, estimate those parts separately and add them to the flat slab volume.
Sources
- Quikrete product yields — bagged concrete mix yield references
- Sakrete bagged concrete references — common bag sizes and concrete mix guidance
- ConcreteNetwork concrete price guide — ready-mix and installed concrete cost context
Reviewed for estimating accuracy
Last updated: June 20, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
Related calculators
Other concrete shapes
FAQ
Concrete slab questions
Answers for common slab sizes, thickness, bags vs ready-mix, waste allowance, and quote limitations.
How many 80 lb bags of concrete do I need for a 10x10 slab? + -
For a 10 ft by 10 ft slab at 4 inches thick, the calculator estimates about 1.36 cubic yards with the default 10% waste, or about 62 bags of 80 lb concrete mix. The waste percentage is editable.
How thick should a concrete slab be? + -
Many patios, walkways, and shed pads use a 4 inch slab. Driveways and heavier loads often use 5 to 6 inches or a reinforced design. Always verify the required thickness for your project and local conditions.
Should I use bags or ready-mix for a slab? + -
Small slabs may be practical with bags. Larger slabs can require dozens or hundreds of bags, so ready-mix is often easier to place consistently. Compare the bag count, ready-mix yards, and delivery minimums before deciding.
Does the slab calculator include waste? + -
Yes. The slab calculator defaults to a 10% waste allowance and lets you type a custom percentage. This helps cover uneven subgrade, over-excavation, spillage, and small measurement errors, and it also lets you compare different buying assumptions.
Is this concrete slab estimate a quote? + -
No. It is an estimate for planning material quantities and rough material cost. Confirm product yield, price, delivery minimums, reinforcement, base preparation, and finishing requirements with your supplier or contractor.