Concrete Countertop Mix Calculator
Pouring a concrete countertop starts with one number: the volume of concrete the slab will hold. Get that right and the bag count and mix weight follow directly. This concrete countertop mix calculator takes the countertop length and width in feet and the thickness in inches, converts everything to consistent units, and returns the slab volume in cubic feet, the total mix weight, and how many bags of countertop mix you need. The volume is length times width times thickness, with the thickness converted from inches to feet. The mix weight uses the density of cured concrete, around 150 pounds per cubic foot, and the bag count divides that weight by the yield of a standard bag. Every figure here is computed deterministically from your dimensions and the density and bag size you enter, so the same slab always returns the same result. Enter your measurements below to size a mix order before you build a mold, compare slab thicknesses, or check a leftover bag count, with a worked example that reconciles exactly to the calculator defaults so you can follow each step. Always mix a little extra, since some material is lost to the mixer, the mold, and trimming the edges.
Slab volume equals length times width times thickness, and mix weight is volume times concrete density. A 6 ft by 2 ft top at 1.5 in thick is 1.50 cu ft, about 225.00 lb, needing 3 bags of 80 lb mix.
Concrete countertop mix formula
volume (cu ft) = length x width x (thickness / 12)
mix weight (lb) = volume x 150 lb per cu ft
bags = roundup( mix weight / bag yield )
length and width in feet, thickness in inches
Thickness is divided by 12 to convert inches to feet before multiplying. Cured concrete weighs about 150 pounds per cubic foot, and dividing that weight by the bag yield, rounded up, gives the number of bags.
Worked example
Take a countertop 6 feet long, 2 feet wide, and 1.5 inches thick, using 80 pound bags of mix.
- Volume: 6 x 2 x (1.5 / 12) = 6 x 2 x 0.125 = 1.50 cu ft
- Mix weight: 1.50 x 150 = 225.00 lb
- Bags: 225.00 / 80 = 2.81, rounded up to 3 bags
The slab holds 1.50 cubic feet, weighs about 225.00 pounds, and needs 3 bags of 80 pound mix, matching the calculator's default inputs exactly. Mix a little extra for losses.
Concrete Countertop Mix Calculator: frequently asked questions
What density should I use for concrete?
Standard cured concrete weighs roughly 150 pounds per cubic foot, which this calculator uses for the mix weight. Lightweight countertop mixes can be lower, so if your product lists a different density, treat the weight as an estimate and follow the bag's own yield chart for bag count.
How thick should a concrete countertop be?
Cast countertops are commonly between 1.5 and 2 inches thick, with reinforcement inside. Thicker slabs are heavier and use more mix, so confirm your cabinets and supports can carry the weight before increasing the thickness.
Why round the bag count up?
You cannot buy part of a bag, and some mix is always lost in the mixer, the mold, and edge trimming. Rounding up, and ideally adding a spare bag, ensures you can finish the pour without stopping to buy more, which risks a cold joint.
Does this include the bag yield by volume?
This calculator bases bags on weight, dividing the slab weight by the bag weight you enter. Many bags also list a volume yield in cubic feet, so you can cross-check by dividing the slab volume by the bag's stated volume yield.
What about sinks or cutouts?
Cutouts for a sink or cooktop reduce the volume slightly, but the saved material is small and useful as a buffer against losses. For a large cutout, subtract its volume from the slab volume before reading the bag count if you want a tighter estimate.
Official sources
- Measurement, units and dimensional standards: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.