Concrete Countertop Calculator
A concrete countertop calculator divides slab cu ft by 0.6 per 80-lb bag and rounds up: an 8 ft × 26 in top at 2 in is 2.89 cu ft, or 5 bags (6 with 10% extra).
How many bags of concrete for a countertop?
A concrete countertop calculator multiplies the slab’s length and width in feet by its thickness in inches ÷ 12 to get cubic feet, then divides by 0.6, the cubic feet one 80-lb bag of mix yields. The result rounds up to whole bags. An 8 ft run of standard 26-inch-deep counter (2.17 ft) poured 2 inches thick holds 2.89 cubic feet, which is 4.82 bags, so you buy 5. Tick the 10% waste box and it becomes 6.
Enter the top’s length, its depth front to back as the width, the slab thickness, and your price per bag. The calculator returns bags and the cost of those bags.
The formula in plain words
- Cubic feet = length × width × (thickness in inches ÷ 12)
- Bags = cubic feet ÷ 0.6
- With waste = bags × 1.10
- Round up to a whole bag, then multiply by price per bag
A countertop is a thin slab, so small thickness errors matter. A quarter inch extra on a 2-inch top adds 12.5% more concrete.
Worked examples
Both use $7 per bag.
- Kitchen run, 8 ft × 26 in (2.17 ft), 2 in thick**
- Volume: 8 × 2.17 × (2 ÷ 12) = 2.89 cu ft
- Bags: 2.89 ÷ 0.6 = 4.82, rounded up to 5 bags ($35)
- With 10% waste: 4.82 × 1.10 = 5.30, rounded up to 6 bags ($42)
- Weight: 2.89 × 150 = about 434 lb
- Kitchen island, 6 × 3.5 ft, 2 in thick**
- Volume: 6 × 3.5 × (2 ÷ 12) = 3.50 cu ft
- Bags: 3.50 ÷ 0.6 = 5.83, rounded up to 6 bags ($42)
- With 10% waste: 6.42, rounded up to 7 bags ($49)
- Weight: 3.50 × 150 = 525 lb
The island holds more concrete than the longer wall run because it is much deeper front to back.
Bags and weight by slab thickness
Per 10 sq ft of countertop, at 0.6 cu ft per 80-lb bag and 150 lb per cu ft.
| Thickness | Cu ft per 10 sq ft | Bags per 10 sq ft | Weight per sq ft |
|---|---|---|---|
| 1.5 in | 1.25 | 2.08 | 18.8 lb |
| 2 in | 1.67 | 2.78 | 25.0 lb |
| 2.5 in | 2.08 | 3.47 | 31.3 lb |
| 3 in | 2.50 | 4.17 | 37.5 lb |
Multiply by your area in tens of square feet, then round the bags up. A 30 sq ft kitchen at 1.5 inches needs 3 × 2.08 = 6.25, so 7 bags before waste.
Precast or poured in place?
Precast tops are cast upside down in a melamine mold in a shop or garage, then flipped, polished, and carried in. The weight matters here: the 434 lb kitchen run usually has to be cast in two or three pieces. Cast-in-place tops avoid lifting but must be finished on the cabinets.
How to measure
- Measure the finished top, including the overhang past the cabinet face, usually about 1 to 1.5 inches.
- Split L-shapes and U-shapes into rectangles and add the bags. Do not double count the corner square.
- Ignore sink cutouts when ordering. The concrete you save is small, and the spare covers spillage.
- Add drop edges separately. A 3-inch-tall front edge on a 1.5-inch slab is a strip of extra concrete. Enter it as its own length × width × depth.
- Check the mold depth once it is built. Forms often end up a touch deeper than planned.
Common mistakes
- Mixing batches unevenly. Each bag needs the same water. Extra water in one batch shows as a lighter, weaker patch.
- Forgetting the backsplash. An integral backsplash is extra concrete. Measure it as its own slab.
- Skipping reinforcement at cutouts. Cracks almost always start at the inside corners of a sink hole.
- Pouring without a vibration plan. Tap the mold sides or use a vibrator to raise air bubbles, or the face shows pinholes.
- Ordering the exact count. One short bag stops the pour while the first batches start to set.
Related calculators
For other small pours by the bag, use the concrete bag calculator or the brand-based Quikrete calculator. To check total slab weight for supports, the concrete weight calculator gives the number. Compare a DIY pour with stone or quartz using the countertop cost calculator.
Frequently asked questions
How thick should a concrete countertop be?
Most cast-in-place and precast concrete countertops are 1.5 to 2 inches thick, with reinforcement. A 2-inch slab weighs about 25 lb per sq ft and a 1.5-inch slab about 19 lb. Thicker 2.5 to 3 inch tops look chunkier but add weight fast; many makers build a thick-looking front edge with a deeper drop edge instead of pouring the whole slab thick.
Can I use regular 80-lb concrete mix for a countertop?
You can, but most builders use a countertop mix or a high-strength mix with fine aggregate and fibers. It finishes smoother, resists cracks better, and polishes without exposing large stone. This calculator uses the 0.6 cu ft yield of a standard 80-lb bag; specialty mixes may yield a little less, so check the bag.
Does a concrete countertop need reinforcement?
Yes. A thin slab spanning cabinets cracks without it. Common choices are welded wire or rebar set in the middle of the slab's thickness, fiber mixed into the concrete, or both. Add extra reinforcement around sink and cooktop cutouts, where the slab is narrowest.
How much does a concrete countertop weigh?
At about 150 lb per cubic foot, the 8 ft × 26 in × 2 in top in the example is 2.89 cu ft, or roughly 434 lb. That is about 25 lb per sq ft of countertop. Standard base cabinets on a level floor usually carry it, but long overhangs and islands need support brackets or corbels.
Should I round up bag count for a countertop pour?
Yes. The calculator already rounds up, and the 10% waste box adds more. Running short mid-pour leaves a cold joint and a color line across the top, so most people buy the waste-on count plus one spare bag. Unopened bags can usually be returned.
Estimates only. Verify quantities with your supplier before purchasing.