Concrete Countertop Calculator
Find how many 80-lb bags of high-strength concrete mix you need for a cast countertop, plus total cost at your price per bag.
How this calculator works
A concrete countertop is a thin, precisely sized slab, so this calculator converts its length, width, and thickness into cubic feet, then divides by the 0.6 cubic feet an 80-lb bag yields once mixed to give a bag count.
Formula: Cubic yards = (Length ft × Width ft × Depth ft) ÷ 27. Bags = (Cubic yards × 27) ÷ 0.6.
Worked example
An 8 ft × 2.17 ft (26 in) countertop slab at a 2-inch depth:
- Depth in feet: 2 ÷ 12 = 0.1667 ft
- Cubic feet: 8 × 2.17 × 0.1667 ≈ 2.8933 ft³
- Bags: 2.8933 ÷ 0.6 ≈ 4.82 bags
- At $7/bag, that’s $33.76 before waste.
Cost reference
| Countertop size | Depth | Bags needed (80-lb) | Cost at $7/bag |
|---|---|---|---|
| 4 ft × 1.085 ft | 2 in | 1.21 bags | $8.47 |
| 8 ft × 2.17 ft | 2 in | 4.82 bags | $33.76 |
| 16 ft × 4.34 ft | 2 in | 19.29 bags | $135.03 |
How to measure your countertop
Measure the finished slab’s length and width along its top surface in feet, treating an L-shaped or multi-piece counter as separate rectangular sections added together. Use the slab’s actual poured thickness as depth — most countertops run 1.5-2 inches, thicker at any front edge detail or drip edge, which should be calculated as a separate strip if it adds noticeably more concrete.
Frequently asked questions
How thick should a concrete countertop be?
1.5-2 inches is the standard thickness for a cast concrete countertop — thick enough for strength once reinforced, without adding unnecessary weight to the cabinets supporting it. Thicker slabs (2.5-3 in) are sometimes used for a chunkier look but add substantial weight and concrete cost.
Can I use regular 80-lb concrete mix for a countertop, or do I need something special?
Countertops are usually cast from a high-strength or countertop-specific mix with finer aggregate, lower water content, and often fiber reinforcement for a smoother, more crack-resistant finish than standard 80-lb general-purpose mix. This calculator estimates bag count using standard 80-lb bag yield; check your chosen mix's actual yield per bag since specialty countertop mixes sometimes differ slightly.
Does a concrete countertop need reinforcement?
Yes, almost always — a thin, cantilevered slab like a countertop is prone to cracking without reinforcement. Common approaches include a layer of galvanized wire mesh, rebar for larger spans, or fiber reinforcement mixed directly into the concrete, especially around sink and cooktop cutouts where the slab is weakest.
How much does the countertop's weight add to cabinet loading?
Concrete weighs roughly 150 lbs per cubic foot, so an 8 ft × 2.17 ft × 2 in slab (about 2.9 cubic feet) weighs around 435 lbs before counting the mold and any embedded reinforcement. Confirm your base cabinets or support structure can handle the load — concrete countertops are significantly heavier than laminate, wood, or most stone alternatives per square foot.
Should I round up bag count for a countertop pour?
Yes — running short mid-pour on a countertop is worse than most other projects since the mix needs to go in continuously to avoid visible cold joints or color variation across the visible top surface. Buy at least one extra bag beyond the calculated (rounded-up) count as insurance.
Estimates only. Verify quantities with your supplier before purchasing.